Working out a pressure problem in the coolant system

[Arnie91]

So as some of you might know, i've been working on fixing my A4 B6 Cab. It's running great apart from a continuing issue of coolant loss through pressure.

I lost coolant through an upper radiator hose which wasn't secured. But with that solved. My coolant tank is less than half full just after a day, this could be because of a spring band clamp which is messed up, but I was starting to look into a head gasket issue.

The next day I was driving at night, this time with the upper radiator hose fully secured, and it looks as if the coolant came out of the reservoir due to high pressure, or from the cap releasing pressure, as I filled it back up and there were no leaks?

As the head gasket has a number of ways in which is can be blown. I did a compression test and found these values:


Cylinder
1) 171
2) 172
3) 170
4) 171

These seem like typically good ratings for an engine with 120k miles. So if gas isn't escaping into the coolant channels in the engine, then why do I continue to get high pressure?

I'll be doing a leak down test when the kit arrives.

[redline380]

Pressurize coolant system, find leaks.

[Arnie91]

Pressurize coolant system, find leaks.

Are there any guides to making a DIY pressure tester?

Also that isn't necessarily going to fix the pressure problem?

[customa4]

Make sure your coolant tank and cap are in good working order. The cap is designed to release pressure if it gets too high. If it's not doing it's job you're probably losing the coolant out of the tank.

Coolant Pressure Tester DIY

You can also rent a coolant pressure tester kit from Advanced Auto for pretty much free(the easy way). You just put a deposit on the tool and when you return it they give you all of your money back.

[redline380]

Are there any guides to making a DIY pressure tester?

Not that I know of but it would be hard.

All you would need is another coolant cap and drill a hole in it. Somehow get a fitting to seal (epoxy, etc) and supply regulated air to the system. I wouldnt go over 15 psi. If you can see the gauge go down, you have a leak. Look arounf the enigne bay for coolant coming out.

[Arnie91]

Make sure your coolant tank and cap are in good working order. The cap is designed to release pressure if it gets too high. If it's not doing it's job you're probably losing the coolant out of the tank.

Coolant Pressure Tester DIY

You can also rent a coolant pressure tester kit from Advanced Auto for pretty much free(the easy way). You just put a deposit on the tool and when you return it they give you all of your money back.

The cap is new and seems to function if it blew out pressure.

We don't have the pressure tester kits for rent in the United Kingdom :(

I have a spare cap, epoxy ect so I could make a tester potentially.

[customa4]

Ahh, didn't even look at your location. I guess the DIY link I posted or what redline mentioned are gonna be your best bet.

[redline380]

I have a spare cap, epoxy ect so I could make a tester potentially.

For the $20 in parts (or whatever that equates to in the Queen's currency) it would be a lovely piece to keep around for yourself and others. If you don't have a regulator, they are cheap online.

Pressure testers are pretty cool. My dad had a leak on his Chevy Suburban once. Had a tough time tracking it down exactly. Hooked up a pressure tester and instantly saw coolant streaming out of the radiator.

If you have a particularly difficult time finding a leak, you can put some dye in the coolant and use special goggles to find see where the dye is coming out.

[BARRY]

if you have zero leaks anywhere then your thermostat could be faulty.

this is a german car so i'd imagine there being leaks. common places would be; rear coolant outlet or j-plug. beyond that check all your hose joints as they're secured by O-ring and locking clamp.

what color is your coolant? from what i take it, folks in the UK don't really treat their cars with as much love as we do in america so you might have the wrong fluid. maybe because german cars usually sell with included maintenance and service for x number of years.

if its green fluid that is a red flag.

[Let it snow]

Make sure your coolant tank and cap are in good working order. The cap is designed to release pressure if it gets too high. If it's not doing it's job you're probably losing the coolant out of the tank.

Coolant Pressure Tester DIY

You can also rent a coolant pressure tester kit from Advanced Auto for pretty much free(the easy way). You just put a deposit on the tool and when you return it they give you all of your money back.

This test cusoma4 linked worked for me and you can test the cap too

[customa4]

This test cusoma4 linked worked for me and you can test the cap too

Had that link stashed in my vault of bookmarks.

[Arnie91]

Just driving to work now and th upper radiator hose as developed a leak at the connection, definitely new. I have an air compressor on the way but im limping to work.

The fans arent on which might be the cause of all these problems. At 90 degrees and driving for 40 minutes should I expect the fans to be on?

Best way to diagnose a faulty fan module or fan?

[userbob0001]

I wouldn't take that as useful by itself. The thermostat opens at 212F and the fans come on until it drops to what seems like 205F and the fans cut back off. I haven't looked close while it was hot out, so my experience has the coolant temp dropping pretty quickly.

[diagnosticator]

The large cooling fan on the O.S, is the radiator cooling fan. The smaller NS fan is the A/C condenser cooling fan and runs whenever the A/C is in AUTO mode or manual cooling mode. The radiator cooling fan should not be running when driving normally, the air flow from the forward car velocity provides more than enough cooling air flow to the radiator the rad fan is not needed for normal driving.

Get a sample of coolant, and take/send it to a lube oil analysis lab, have the sample tested for dissolved combustion gasses and pH in the coolant. IF there is dissolved combustion gasses in the coolant, then the head gasket is leaking and that will cause over-pressure of the cooling system even without the engine overheating. When the cooling system pressure exceeds the pressure relief setting of the expansion tank cap, the cap will open and release excess pressure and will take some liquid coolant out with the released system over-pressure gasses. Coolant containing dissolved combustion gasses from a head gasket leak will also become acidic quickly.

[diagnosticator]

So as some of you might know, i've been working on fixing my A4 B6 Cab. It's running great apart from a continuing issue of coolant loss through pressure.

I lost coolant through an upper radiator hose which wasn't secured. But with that solved. My coolant tank is less than half full just after a day, this could be because of a spring band clamp which is messed up, but I was starting to look into a head gasket issue.

The next day I was driving at night, this time with the upper radiator hose fully secured, and it looks as if the coolant came out of the reservoir due to high pressure, or from the cap releasing pressure, as I filled it back up and there were no leaks?

As the head gasket has a number of ways in which is can be blown. I did a compression test and found these values:


Cylinder
1) 171
2) 172
3) 170
4) 171

These seem like typically good ratings for an engine with 120k miles. So if gas isn't escaping into the coolant channels in the engine, then why do I continue to get high pressure?

I'll be doing a leak down test when the kit arrives.

Because the likely head gasket leak is not severe enough to be able to leak enough compressed intake air necessary to reduce the compression pressure from the normal value. The high combustion pressures normally developed is forcing some combustion gasses past the gasket leak location into the cooling system at a relativity slow rate.

[Arnie91]

The large cooling fan on the O.S, is the radiator cooling fan. The smaller NS fan is the A/C condenser cooling fan and runs whenever the A/C is in AUTO mode or manual cooling mode. The radiator cooling fan should not be running when driving normally, the air flow from the forward car velocity provides more than enough cooling air flow to the radiator the rad fan is not needed for normal driving.

Get a sample of coolant, and take/send it to a lube oil analysis lab, have the sample tested for dissolved combustion gasses and pH in the coolant. IF there is dissolved combustion gasses in the coolant, then the head gasket is leaking and that will cause over-pressure of the cooling system even without the engine overheating. When the cooling system pressure exceeds the pressure relief setting of the expansion tank cap, the cap will open and release excess pressure and will take some liquid coolant out with the released system over-pressure gasses. Coolant containing dissolved combustion gasses from a head gasket leak will also become acidic quickly.

Because the likely head gasket leak is not severe enough to be able to leak enough compressed intake air necessary to reduce the compression pressure from the normal value. The high combustion pressures normally developed is forcing some combustion gasses past the gasket leak location into the cooling system at a relativity slow rate.

I know that the fan itself does work. A couple months ago before starting the work. I had a the coolant flange blow up, after a quick fix the Fans would stay on completely over the course of a few weeks as I went to and from work, The engine/coolant temp stayed at 50 degrees (Lowest point on gauge) which at the time was great.

I would have thought surely for such a big engine, it's definitely very very hot under the bay. Almost everything is very hot to the touch, surely the fans would come on now and again? I guess not since im only seeing 90 degrees on the temperature gauge.

If this is the head gasket, then is it likely that the head or cylinders are warped or cracked? This will be a bigger job then I can handle so it might just have to be a shop job :(

How likely that it's just the gasket itself?

Edit: I've just realised that the exhaust gasses coming from the back are most likely steam from moisture in the system. I always thought it was just because the car exhausts are hot due to the turbo.

[Arnie91]

I'm going to do the head gasket myself, as it doesn't seem too far off the DIY needed for the VC.

Anyone recommend a high quality aftermarket gasket and bolts? Also any other engine upgrades I could look at while I'm down in the engine?

[redline380]

I'm going to do the head gasket myself, as it doesn't seem too far off the DIY needed for the VC.

LOL at that. Valve cover work and replacing the head gasket are incredibly different jobs.

[customa4]

LOL at that. Valve cover work and replacing the head gasket are incredibly different jobs.

My thoughts exactly.

If you're mechanically inclined to a certain extent it's definitely a DIY job. The toughest part is timing but that's an easy obstacle to overcome as long as you pay attention to detail. The rest is really just removing and reinstalling parts.

[redline380]

My thoughts exactly.

If you're mechanically inclined to a certain extent it's definitely a DIY job. The toughest part is timing but that's an easy obstacle to overcome as long as you pay attention to detail. The rest is really just removing and reinstalling parts.

I use a paint pen and mark the tbelt and the cam and crank gears so there is zero guessing involved. If a new belt is being installed, just transfer the marks over.

[Arnie91]

The large cooling fan on the O.S, is the radiator cooling fan. The smaller NS fan is the A/C condenser cooling fan and runs whenever the A/C is in AUTO mode or manual cooling mode. The radiator cooling fan should not be running when driving normally, the air flow from the forward car velocity provides more than enough cooling air flow to the radiator the rad fan is not needed for normal driving.

Get a sample of coolant, and take/send it to a lube oil analysis lab, have the sample tested for dissolved combustion gasses and pH in the coolant. IF there is dissolved combustion gasses in the coolant, then the head gasket is leaking and that will cause over-pressure of the cooling system even without the engine overheating. When the cooling system pressure exceeds the pressure relief setting of the expansion tank cap, the cap will open and release excess pressure and will take some liquid coolant out with the released system over-pressure gasses. Coolant containing dissolved combustion gasses from a head gasket leak will also become acidic quickly.

LOL at that. Valve cover work and replacing the head gasket are incredibly different jobs.

I've read through what needs to be done, it's not that much more work...

[Arnie91]

My thoughts exactly.

If you're mechanically inclined to a certain extent it's definitely a DIY job. The toughest part is timing but that's an easy obstacle to overcome as long as you pay attention to detail. The rest is really just removing and reinstalling parts.

My thoughts exactly.

[redline380]

I've read through what needs to be done, it's not that much more work...

Um, yeah, it is a lot more work. Not that it means it is a lot longer or more difficult, but there is no denying that a VC gasket is much less work than a HG.

[Arnie91]

so in a last ditch attempt at keeping the car running until I get alternative wheels. I used some steal seal recommended by a mechanic.

I've done a combustion leak test and it's not showing any leaking after 5 minutes of squeezing. I've taken the car on 100 mile round trip and used it for 3 days now. No coolant issues. Wondering if it could of been because I was filled it up too much, or if the heater core was blocked/not bled. I'm going to replace my heater core just in case, and then bleed again.

When I was doing the test. The coolant level was below the minimum by an inch. By the time the engine reached 90 degrees it had increase to half an inch above the maximum line, so the leak therefore earlier in the week could of been due to too much coolant in the system. I find the increasing and decreasing parameters a bit extreme Is that normal?




Also picked up a Silicone TIP and 225 MAF from a member on here!

[poolpo]

so in a last ditch attempt at keeping the car running until I get alternative wheels. I used some steal seal recommended by a mechanic.

I've done a combustion leak test and it's not showing any leaking after 5 minutes of squeezing. I've taken the car on 100 mile round trip and used it for 3 days now. No coolant issues. Wondering if it could of been because I was filled it up too much, or if the heater core was blocked/not bled. I'm going to replace my heater core just in case, and then bleed again.

When I was doing the test. The coolant level was below the minimum by an inch. By the time the engine reached 90 degrees it had increase to half an inch above the maximum line, so the leak therefore earlier in the week could of been due to too much coolant in the system. I find the increasing and decreasing parameters a bit extreme Is that normal?




Also picked up a Silicone TIP and 225 MAF from a member on here!

Hey man,

Did you finally solve your issue? I'm having a similar issue on my A4 B5. See the video.

https://streamable.com/1140zj