Oil Pressure and testing Discussion Thread

[Theiceman]

Updated 05/17/2019
- added Mileage
- put back pics i accidentally deleted
- added info on switch specs and pressure circuit design.

As most of us know by now, oil pressure issues on these engines are becoming quite common and it seams someone is posting every week with Oil Pressure issues. I have started this thread to discuss oil pressure in general, specifications of it testing of it, options of what to do for monitoring , what good looks like and so on ...
I am hoping to leave the causes of low oil pressure to other threads and more just discuss the generalities of it. If someone wants to post all the causes that's fine , but i just wanted to post something for those just heading down the oil pressure road and things that can be done .

So lets start with what we know .

1. Specifications for oil pressure on the A4B7 engine .

( i know someone posted detail on this on a thread form the bentley manual but i just cant find it , hopefully someone will post or send me a PM and i will update this piece. )
Idle 1-1.2 bar or (14.5-17.4 PSI )
2000 RPM 2.7-4.5 bar (39-65 PSI)
3000 RPM 3.5-4.5 Bar (51-65 PSI)

All measurements at 80C

2. Our cars do not have an oil pressure gauge or a way to monitor actual real time oil pressure, they simply use a preset switch that turns on the idiot light below a predetermined value. It is located in the oil filter housing behind the oil cooler

3. The oil pressure is NOT monitored at idle. i know this because with mine disconnected I started the car and had no indications until i hit about 1200 rpm. This has also been validated by others.

4. Early cars use a 1 pin oil switch, later cars use a 2 pin switch. if you are considering replacing the oil pressure switch make sure you order the correct one.

5. The thread for the oil pressure switch is a 10mm by 1.0mm thread pitch , it is NOT NPT thread. Most gauges for testing oil pressure are NPT so you will need the correct adapter to connect a commercial oil pressure gauge to your car.

6. The pressure switch is rated at 1.2-1.6 Bar , which i think means the light will come on when the pressure is below 17.5-23.2 psi , or between the two maybe ?
This would explain why the car does not look at the switch till about 1200 RPM

7. The pressure switch is normally open and depends on oil pressure to close and ground the switch keeping it at a logic low. If the signal goes high the oil pressure light will set, this could be due to low oil pressure which will cause the switch to go open, or a broken ground wire on the early style switch (this switch has a crimped/soldered connection that can come loose). A broken ground wire will cause the circuit to go open and simulate low oil pressure

Oil pressure sensor relocation kits...

there are some great kits available on relocating the oil pressure switch . Why you might ask ? . Well because of the points noted above some people want to "T" in a real sender so they can monitor actual pressure. I am looking at doing this myself.

here is a great thread by Phill on relocation and adding a sender and a read out to his factory display.

https://www.audizine.com/forum/showt...ssure-Read-Out

Incorporating the system into your read out is very nice but spendy and not totally necessary . if you would like to relocate your sender so you can simply add your own sender and gauge this option is available.


https://www.ecstuning.com/b-42-draft...t/8662771~42d/

as my dad would say " that's is a good bit of kit". very cost effective and allows you to move your switch and add in your own sender for a gauge . Interesting to note that the hose is actually NPT threads but goes to an adapter to metric on one end to go into your filter housing and the other end goes into the block which has one NPT fitting.

If you are not up to this challenge, then we have the following option available. Even more cost effective.

https://www.ecstuning.com/b-new-sout...o-port/con017/

This one allows you to tap into a turbo feed line to monitor the pressure and add an NPT sensor. it replaces the factory banjo bolt with one that has an NPT tap in the head. very simple solution. If anyone has done this please post a pic.

All this is in aid of allowing you to actually monitor your oil pressure.

There are even some kits that run tubing to the gauge inside your car. acting as a mechanical gauge ... umm not for me , sender and gauge is good for me.


So what if you just want to boost your oil pressure at idle ?

This can be done somewhat through vag-com by changing a setting . When i find this info i will post it here for those of you who have access to vag-com . it allows you to boost your idle which might just do the trick for a lot of people who feel they are too low at idle ...

So i took a look at my car which flashed a low idle last week but then it went away. About a month ago i replaced the housing and thought i should put a new sensor in , which i didnt :). so not sure if that is causing issues but as a precaution i parked the car until pressure could be checked.

The results of my car ...

I tried to get pics of the RPM, Engine Temp, and oil Pressure.... My car has 305k Km on it which is about 180K miles which i did not capture in pics.

eg.

18-20 PSI at idle....



50 PSI at 2K



65 PSI at 3K



I checked with my mechanic buddy who works on Mac trucks all day long and he says these pressures are absolutely fine and i have nothing to worry about.
So here's hoping ..



The take away.

So i hope this thread has been helpful to those of you just coming here looking for why your pressure light came on. I will add to this thread as we learn more about oil pressure monitoring in this car.
The real take away is if your oil pressure light comes on it is not because of low pressure at idle. It is because you were not above 17.5-23.2 psi by the time you hit about 1200 RPM. So this is what you should be checking for. Also oil pressure is NOT to be trifled with, low oil pressure can destroy your engine in seconds - minutes. If you are not sure get it professional diagnosed and make informed decisions.
This car is actually my sons car, and the one thing he knows is if he sees this light come on, shut down the car immediately. I think when it comes to oil pressure it is always better to be safe than sorry.

Thanks to all those who contributed to the info in this thread

would you like to contribute ?

If you want to post pics to this thread please do so we can all learn . Cyriks pics are the best showing , pressure, RPM , temp and Mileage.

To post pics use imgur and copy and paste the link for your pic , this provides excellent resolution.

eg.

[james12lucy]

Awesome thread, Iceman.

I can confirm the 1 and 2 prong oil pressure sensors on early and later models. I believe the 1 prong came on the 2005.5 and 2006, and was replaced in the 2007 model year. The one prong also has a separate ground wire, which is prone to failing under heat.

I will be adding the 42DD relocation kit on the near future and running both a mechanical gauge, and the OEM gauge (which will connect to my AiM datalogger) in the race car. I’ll be able to provide exact pressure readings at various RPM, and will compare electrical vs. Mechanical.

Increasing idle RPM does increase oil pressure and can be done through VAG-COM and Maestro.

Again, thanks for creating this thread. Awesome info.


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[Theiceman]

Thanks James ... my buddy who loaned me the pressure gauge said screw the cell phone, just leave the oil pressure gauge in the holder !!! lol . wont miss low oil pressure then !!

[james12lucy]

Thanks James ... my buddy who loaned me the pressure gauge said screw the cell phone, just leave the oil pressure gauge in the holder !!! lol . wont miss low oil pressure then !!

Exactly! Seriously, it’s cheap insurance. Also, it allows you to see if typical pressures slowly start to drop or climb over time, instead of just having no oil pressure and likely needing a new engine as a result.


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[Cyrik]

This is brilliant and something we've needed on here for a while, thanks iceman! 😁 this should be stickied to prevent confusion for other threads on the matter.

Also for this thread if people are willing to post their pressure readings I'm curious to know if a lower mileage engine will read a higher oil pressure reading vs a higher mileage engine.

[Theiceman]

Exactly my thoughts Cyrik. A place to put their pressures or pics as I did so you can see all relevant Information
.Temp rpm and pressure

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[james12lucy]

Exactly my thoughts Cyrik. A place to put their pressures or pics as I did so you can see all relevant Information
.Temp rpm and pressure

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To add to this, we can get into mileage as well. Also, I’ll be testing on a built engine, so thinking tighter tolerances will mean higher pressures.


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[Brillo]

Nice start Theiceman, appreciate your efforts. My Jaguar and both of my planes have oil pressure gauges and I always monitor them. The planes have oil temperature as well (piston powered planes are engine critical of course - can't just pull over and park on a cloud).

I'm going to get the ECSTuning relocation kit. I just need to decide on the proper gauge so I would like to hear of others' experiences with various oil pressure gauges.

[Cyrik]

Exactly my thoughts Cyrik. A place to put their pressures or pics as I did so you can see all relevant Information
.Temp rpm and pressure

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In that case might as well start off by posting mine haha.

Fully warmed up, My idle:


2k RPM:


3k RPM:


My issue isn't what this thread is about, not threadjacking here but in short I found large metal shavings in my oil pan, covered this over in another thread. I've concluded that some sort of bearings in the engine are shot. I get the low oil pressure warning intermittently as my car is just under spec which is enough to trigger the light every once in a while.

Oil pressure is not to be taken lightly on these cars. If you're having a similar issue, be prepared to spend lots of hours and money underneath the car and all the headaches that go with it if you come across a similar issue.

Again, my issue is NOT what this thread is about. Showing what's normal and what's not. 😊 (My pressure is NOT normal!)

[Brillo]

To add to this, we can get into mileage as well. Also, I’ll be testing on a built engine, so thinking tighter tolerances will mean higher pressures.

Right, higher pressures until you hit the RPM where the relief valve in the oil pump opens and starts dumping excess oil back to the sump. I've read that it is set at 65 to 70psi. I've never personally worked on the oil pump balane shaft module but suspect a number of oil pressure problems relate to malfunctions of the oil relief valve. Again, this is mostly speculation on my part.

[Theiceman]

Cyrik what oil and weight you running? I forgot to mention I'm running mobil 1 0w40

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[Cyrik]

Cyrik what oil and weight you running? I forgot to mention I'm running mobil 1 0w40

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Castrol Edge 5w40, I'm thinking of stepping up the weight for the sake of better oil pressure.

[EvolutionArmory]

Right, higher pressures until you hit the RPM where the relief valve in the oil pump opens and starts dumping excess oil back to the sump. I've read that it is set at 65 to 70psi. I've never personally worked on the oil pump balane shaft module but suspect a number of oil pressure problems relate to malfunctions of the oil relief valve. Again, this is mostly speculation on my part.

No matter how complicated it looks, it’s still just an oil pump and there can only be a few reasons why the pump doesn’t produce enough pressure/flow.

I believe you’re right and most of them are PRV related.

Other possibilities are a clogged pick up restricting flow

Wear on the balance shafts causing an internal pressure leak

The pump gear rod is stripping and not generating enough flow

The chain or tensioner failed (catastrophic failure, you’re basically screwed if this happens)

There aren’t that many possibilities for low oil pressure and most of the causes involve a new pump, unfortunately, except for the pick up tube being clogged.

If you want to get a better look at failed oil pumps, look at the TDI pump failures. They use a similar design and have a significantly higher failure rate than we do. You might be able to get some insight as to what’s failing from their experiences.

Basically, if you have legit low oil pressure and it’s not a faulty switch you should drop the pan and check the pick up tube and the balance shafts for play. If those 2 things are good, most likely the pump PRV is faulty.

[Brillo]

Castrol Edge 5w40, I'm thinking of stepping up the weight for the sake of better oil pressure.

Do not do this unless you strongly suspect your main crank and rod bearings are worn out because it will reduce oil flow to critical bearing parts.

[Cyrik]

Do not do this unless you strongly suspect your main crank and rod bearings are worn out because it will reduce oil flow to critical bearing parts.

Good to know, thanks. I'll keep using 5w40.

I'm not worried about the crank as it's forged but I suspect rod bearings are the culprit. Only way of knowing for sure is by tearing apart the bottom end of the motor.

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[Brillo]

Good to know, thanks. I'll keep using 5w40.

I'm not worried about the crank as it's forged but I suspect rod bearings are the culprit. Only way of knowing for sure is by tearing apart the bottom end of the motor.

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If you suspect rod or main bearing degeneration it might be worthwhile to send an used oil sample to Blackstone Labs to get an analysis. You'll need 3 or4k miles on it first. Oil analysis isn't totally definitive but if it's very normal, that could give you some peace of mind. On the other hand, if iron (Fe) is abnormally high it would indicate a wear problem, usually cams or crankshaft. The analysis not expensive, <$40.

https://www.blackstone-labs.com/?ses...ier55%29%29%2F

[Cyrik]

If you suspect rod or main bearing degeneration it might be worthwhile to send an used oil sample to Blackstone Labs to get an analysis. You'll need 3 or4k miles on it first. Oil analysis isn't totally definitive but if it's very normal, that could give you some peace of mind. On the other hand, if iron (Fe) is abnormally high it would indicate a wear problem, usually cams or crankshaft. The analysis not expensive, <$40.

I might actually look into this as I've seen YouTube videos on it before, thanks for the tip.

On another note, rather than trying to find a tee fitting to connect the sensor along with a gauge, is there a way to disable the oil pressure warning through Vagcom? Getting annoying as I can't see my gas mileage lol.

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[canadianA4B7]

Do not do this unless you strongly suspect your main crank and rod bearings are worn out because it will reduce oil flow to critical bearing parts.

What I don’t get is how high of numbers the race synthetic oils are rated for and they’re manufacturers tell you it’s legit no issues running in a good number of engines. I’ve tested a few different weights of oils and sent most in for inspections never had any issues other then minimal pressure differences. And trust me I understand what your stating I’ve listened to your advice and agree, but if the results show no differences..... I dunno

I might actually look into this as I've seen YouTube videos on it before, thanks for the tip.

On another note, rather than trying to find a tee fitting to connect the sensor along with a gauge, is there a way to disable the oil pressure warning through Vagcom? Getting annoying as I can't see my gas mileage lol.

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I grabbed a T fitting I believe it was 1/8” npt then re threaded the 1 side to be M10 whatever the sensor threads are. $17.99 for the T fitting and I run oil pressure digital, oil temp digital and mechanical pressure gauge as well as oem. Might be best to fix rather then code out the light. Maestro had a section which can turn off just about any code doesn’t mean the issue is fixed.

[Charles.waite]

I have the New South adapter (ECS link in OP) for the turbo oil feed and plan to install it with my new engine soon-ish.

I have a VEI digital Boost/Oil-Pressure gauge (LINK) going into a Podi Steering column pod.

As much as I'm curious what sort of oil pressure my current engine is running given its checkered past (CF, HPFP, and Cam failure 50k miles ago) I'm not willing to invest the time and effort to install it into my engine bay right now given how difficult it is to get to the oil feed line's banjo bolt.

[Brillo]

What I don’t get is how high of numbers the race synthetic oils are rated for and they’re manufacturers tell you it’s legit no issues running in a good number of engines. I’ve tested a few different weights of oils and sent most in for inspections never had any issues other then minimal pressure differences. And trust me I understand what your stating I’ve listened to your advice and agree, but if the results show no differences..... I dunno

Canadian If I understand what your asking I would say a couple of things. No one who understands engine oils would recommend a race oil for use in a DD engine. Race oils are for racing and the additive package is mainly for extremely high pressure situations and occasionally extrteme temperature conditions that are not encountered in a DD. Additionally, they often lack certain additives such as detergents and typically don't have the alkali rating to combat corrosion byproducts over the much longer OCI found in a DD that aren't important to race oils. The higher viscosity race oils are used in application where higher or extreme oil temperatures might be more likely to be encountered, especially in the older air cooled motorcycle engines, or even some liquid cooled engines that are running in the southwest or some hot desert conditions somewhere in Africa. Also, some race oils are not multiweight oils.

It is a misnomer in today's world that oil viscosity is proportional to protection - just not the case. For the DD wear protection is much more a function of the base polymer and additive package than anything else. I don't know the viscosity of the oil used in Formula 1 racing but it might surprise you to learn how low the viscosity is in Indy cars-more like 30 than 50. Years ago when I volunteered for the TWR Jaguar racing team based out of Valparaiso, IN (mostly at Mid-Ohio and Elkart Lake (Road America)) I tried to find out what synthetic they were using but to no avail - huge secret even though they were sponsored by Castrol Oil at the time. I can tell you is was not a 50 or 60 viscosity oil though. Sometimes the oil was pre-heated and circulated prior to cold engine start.

I don't know of a single manufacturer that would recommend the use of racing oil in their car and you will find that a lot of oil suppliers (that might also sell race oils) caution prospective customer not to use in a DD engine. As an example, Amsoil sells 20, 30, 50, and 60 viscosity racing oils for various racing applications but clearly states "DOMINATOR [racing oil] is not intended for long-term use in passenger cars/light trucks."

Hydrodynamic lubrication of the critical parts of modern car engines depends much more on flow for lubrication and cooling than on viscosity, and that is the basis of my comment to cyrik. A higher viscosity oil may raise the oil pressure to the detriment of good flow and pressure in the critical bearing spaces. In the old days of old oil technology and high mileage V8s and I6s, it was common to throw a higher viscosity in the sump to raise the oil pressure, and it mostly worked. That's just not the current thinking with tighter bearing tolerances, better materials, and superior high performance synthetic oils.

It's a one-off anecdote, but my neighbor who does a lot of driving just ticked over 300k miles in his Maxda CX-9 which has a TC 4cyl engine using exclusively the recommended 5W-20 viscosity synthetic, and claims the engine performance hasn't degraded that he can detect. So those are my thoughts and I'm certainly open to further discussion or criticism.

[Theiceman]

I might actually look into this as I've seen YouTube videos on it before, thanks for the tip.

On another note, rather than trying to find a tee fitting to connect the sensor along with a gauge, is there a way to disable the oil pressure warning through Vagcom? Getting annoying as I can't see my gas mileage lol.

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I would imagine jumpering the wires on the two wire system would do it, or grounding the single pin would do it. But I think that is really high risk.


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[Jayz691]

Pics of CC please??

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[canadianA4B7]

Thanks Brillo I actually think you’ve just given the info I did not get from rotella and Castrol.

I’ve got a V8 blower build going on else where and was also discussing some weight numbers with builder there. He’s big on tolerances, numbers and all that fine detail stuff. Bit more info here and I think I’m happy now with the oil info!

[Theiceman]

Cyrik your 2K reading is worrisome in that fact that mine read almost 50 PSI at that RPM, i think this basically confirms my findings that you probably drop below the threshold at about 1200 RPM , which is triggering your light.
You have just done so much work... you are definitely " bleeding out" somewhere.

[Theiceman]

Canadian If I understand what your asking I would say a couple of things. No one who understands engine oils would recommend a race oil for use in a DD engine. Race oils are for racing and the additive package is mainly for extremely high pressure situations and occasionally extrteme temperature conditions that are not encountered in a DD. Additionally, they often lack certain additives such as detergents and typically don't have the alkali rating to combat corrosion byproducts over the much longer OCI found in a DD that aren't important to race oils. The higher viscosity race oils are used in application where higher or extreme oil temperatures might be more likely to be encountered, especially in the older air cooled motorcycle engines, or even some liquid cooled engines that are running in the southwest or some hot desert conditions somewhere in Africa. Also, some race oils are not multiweight oils.

It is a misnomer in today's world that oil viscosity is proportional to protection - just not the case. For the DD wear protection is much more a function of the base polymer and additive package than anything else. I don't know the viscosity of the oil used in Formula 1 racing but it might surprise you to learn how low the viscosity is in Indy cars-more like 30 than 50. Years ago when I volunteered for the TWR Jaguar racing team based out of Valparaiso, IN (mostly at Mid-Ohio and Elkart Lake (Road America)) I tried to find out what synthetic they were using but to no avail - huge secret even though they were sponsored by Castrol Oil at the time. I can tell you is was not a 50 or 60 viscosity oil though. Sometimes the oil was pre-heated and circulated prior to cold engine start.

I don't know of a single manufacturer that would recommend the use of racing oil in their car and you will find that a lot of oil suppliers (that might also sell race oils) caution prospective customer not to use in a DD engine. As an example, Amsoil sells 20, 30, 50, and 60 viscosity racing oils for various racing applications but clearly states "DOMINATOR [racing oil] is not intended for long-term use in passenger cars/light trucks."

Hydrodynamic lubrication of the critical parts of modern car engines depends much more on flow for lubrication and cooling than on viscosity, and that is the basis of my comment to cyrik. A higher viscosity oil may raise the oil pressure to the detriment of good flow and pressure in the critical bearing spaces. In the old days of old oil technology and high mileage V8s and I6s, it was common to throw a higher viscosity in the sump to raise the oil pressure, and it mostly worked. That's just not the current thinking with tighter bearing tolerances, better materials, and superior high performance synthetic oils.

It's a one-off anecdote, but my neighbor who does a lot of driving just ticked over 300k miles in his Maxda CX-9 which has a TC 4cyl engine using exclusively the recommended 5W-20 viscosity synthetic, and claims the engine performance hasn't degraded that he can detect. So those are my thoughts and I'm certainly open to further discussion or criticism.

for the record i do not want to turn this into an oil thread as there are lots of those and maybe we can move this to a new one, but i can comment on the racing oil is a run 20w50 racing oil in my Porsche, and wanted to contribute a little .
Racing oil has very high Levels of ZDDP ( anti wear properties ) in the order of 1300-1500 ppm . ZDDP was mandated removed from oils under class J oil specs due to the fact it destroys catalytic converters ( this is why you should not run it in your daily driver. ) This oil was allowed to be used in " racing applications" and must be designated that way.
Modern cars have hydraulic lifters that adjust to what is required so having no zddp is not as critical as it once was. Older cars ( like my Porsche ) run flat tappets ( kind of like our cam follower ) and engines get destroyed fast ( read pitted cams and rockers ) in about 30K miles in some cases when it used to take 150 k miles. ZDDP is a crucial element in keeping older cars healthy, in case anyone is interested I run Brad Penn semi synthetic racing oil and when i did my teardown of that engine I had one very small pitted area on one cam lobe. the rest was fine. Which i was okay with. Personally i think these new class J oils are why we are wearing out cam followers personally, but that's definitely a can of worms for another thread :)

[AudiKilla]

I have the 42DD Kit + P3 Cars Multi-Gauge. Engine is healthy with 140KM, never had a damaged cam follower. I use 0w40 Rotella T6 engine oil and a MANN filter.

At IDLE: 19-20 PSI
At 2K: 58-60 PSI

Note, I have raised idle to 750rpm I think through vagcom.

[EvolutionArmory]

Those of you who are using relocation kits and gauges, is there any chance of your pressure readings being off due to having the sensor off the engine and having the additional hoses or piping or is that a non issue?

I guess what I’m thinking is, could the inner diameter of the relocation kit hoses affect the pressure at the sensor and give a false actual pressure reading + or - ? Just thinking out loud.

[Theiceman]

Those of you who are using relocation kits and gauges, is there any chance of your pressure readings being off due to having the sensor off the engine and having the additional hoses or piping or is that a non issue?

I guess what I’m thinking is, could the inner diameter of the relocation kit hoses affect the pressure at the sensor and give a false actual pressure reading + or - ? Just thinking out loud.

im sure this is possible .. the only way to do it would be lots of measurements with a gauge right at the housing , record results, put in relocation kit, record pressure off relocation block and record.
i will definitely do this when i build my own relocation kit.

[AudiKilla]

I don't think so but if someone could test it out that would confirm it.

[EvolutionArmory]

I think this could be key. I would suggest anyone doing actual oil pressure diagnosis should do it at the actual sensor location on the OFH as close to the block as possible. The relocation and gauge in your car is a great way to monitor what’s going on but maybe not for diagnosis. Maybe it would be wise to measure at the block and then compare the readings to your in car gauge and note any possible differences.

[Theiceman]

I think this could be key. I would suggest anyone doing actual oil pressure diagnosis should do it at the actual sensor location on the OFH as close to the block as possible. The relocation and gauge in your car is a great way to monitor what’s going on but maybe not for diagnosis. Maybe it would be wise to measure at the block and then compare the readings to your in car gauge and note any possible differences.

would be awesome if you could dial a calibration factor into the gauge ..

[Charles.waite]

Those of you who are using relocation kits and gauges, is there any chance of your pressure readings being off due to having the sensor off the engine and having the additional hoses or piping or is that a non issue?

I guess what I’m thinking is, could the inner diameter of the relocation kit hoses affect the pressure at the sensor and give a false actual pressure reading + or - ? Just thinking out loud.

It shouldn't matter because there isn't any flow through the tubing for the gauge, its just a deadend. If you were reading oil temp off a deadend extension that would be very inaccurate, but I think you're good on the pressure front.

[Cyrik]

It shouldn't matter because there isn't any flow through the tubing for the gauge, its just a deadend. If you were reading oil temp off a deadend extension that would be very inaccurate, but I think you're good on the pressure front.

Can confirm this, tested my oil pressure with a 1 foot hose and my 8 foot hose.

Pressure readings were the exact same throughout. Both tests were consistent.

[EvolutionArmory]

But what if you change the inner diameter of the tube? I doubt length would throw off the reading too much but the inner diameter of the tube you use could? Does that pressure then change? Maybe it doesn’t. I don’t know for sure, this is just how I think. I try to imagine every possible thing that could affect the outcome of what I’m doing.

If the relocation kits can’t affect the readings negatively then kits and aftermarket gauges are probably worth doing on all of our cars 😀

[Charles.waite]

Psi is measured at the sensor, not IN the tube. It’s pounds per square inch. The area component should insure the readings are consistent because, again, there is no flow through the tube.

[Cyrik]

Psi is measured at the sensor, not IN the tube. It’s pounds per square inch. The area component should insure the readings are consistent because, again, there is no flow through the tube.

^ This.

Mechanical gauges are the most accurate test you can do, as long as you don't have any leaks around the fittings or the port you're tapping pressure into you'll always get an accurate reading.

...unless of course your gauge isn't accurate, but that's easy to tell if you have a second one available.

[Charles.waite]

Just as an aside, a REALLY restrictive hose could cause a delay in gauge response, as pressure might take a while to transfer through a really small aperture, but otherwise I don't think hose size really makes a difference either way.

[EvolutionArmory]

Thanks for the clarification. It was just a thought that ran through my head.

[Theiceman]

What about this thought ! You hook up a 12 inch line to your t block with switch and gauge sensor
How does the oil get there since it's a dead head ? Would you just be pushing on an air plug that can't be displaced?

Do you have to prime it somehow ? Otherwise i think you would get a lot of needle bounce no ?

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[2006b7a4]

Picked up an oil pressure gauge from harbor freight today because this thread scared me. Results are
"cold start" 60 psi (it was almost 90f degrees out)
let it idle until oil was 176f (or 80c), oil pressure slowly dropped to 22 psi
idle: 22 psi
2k rpm: 50 psi
3k rpm: 60-62 psi

I was very glad to see that, I wonder how accurate the gauge is though considering it was from harbor freight.