Cooling Issue

[prizmatik]

I have a 1998 1.8T, my question is, does the electrical fan turn on to cool the engine, when not using the A/C?

[Seerlah]

The fans cool the radiator, that cools the coolant, that cools the engine block. I believe the electric fan is triggered when the coolant reaches a certain temp, via sensor located in the lower radiator hose by the smic. Maybe someone can correct me if I'm wrong.

[prizmatik]

Thats exactly what I thought too. For some reason after pulling the engine out, and reinstalling, the fan is not turning on.

[Seerlah]

Maybe someone can chimme in as to when the electric fan is triggered. Then you can use Vag Com to check your coolant temp, to see if it indeed does or does not trigger at said temp. If it doesn't, I would look into either the coolant fan switch in the lower radiator hose being faulty, or your electircal wiring somewhere is faulty. And just because we all do stuff like this when working on our cars, the sensor is plugged in...correct?

I'm no expert, but this is what I would do, if it were me. Than afterwards, consult the pros on what to do next.

[prizmatik]

Yep, sensor is plugged in. I just found an old fan switch from a parts car, I am going to install it right now to see if it makes a difference.

[prizmatik]

I installed the other fan switch, but the fan is not coming on. Vag-Com showed a fault code for the coolant temperature sensor (no check engine light though). The guage has been working fine, even when the engine begins to get hotter. I hope I have a spare ECT sensor available, and hope that it solves my problem.

[rockersteady]

The B5 electric fan is AC only, when condenser temp rises the fan switches on.

The non electric viscous fan as you know turns all the time, but the hub is free wheel and only turns due to initial bearing drag. When the surrounding air-( block radiator heated) heats up the viscous bearing the drag increases and the fan will turn at same rate as driven pulley, force cooling. mostly at idle only if engine is at opperating temp, or the radiator fins aren't passing enough air

[walky_talky20]

The electric fan has 2 speeds, high and low. Low speed is engaged whenever the a/c is on. High speed will engage if ever the a/c high-pressure switch closes.

Further, the electric fan is also controlled by the dual-thermal-fan-switch, which is completely independent of a/c operation. The Low Speed of the fan will engage if the coolant temp at the radiator outlet rises above 95C. The High Speed will engage when the outlet temp rises above 102C. If the viscous fan is operating properly, the electric fan will normally only kick on for stop and go driving with high ambient temps (in which case you usually have your a/c on anyway, giving constant low speed operation regardless).

If the car is overheating and the electric fan has not kicked on, you would want to check if the lower rad hose is hot. It is entirely possible for the lower rad hose to be stone cold while the car is overheating. This would mean either the t-stat is stuck closed (rare), the t-stat is installed backwards (not as rare), or the water pump has failed. Other possible causes could be a plugged radiator or a significant air-lock in the system that is preventing flow.

It is also possible that the coolant temp sensor or the gauge itself is lying, and the car is in fact not overheating - but that should be somewhat obvious (boiling over and what not). You can pretty easily test the fan control system via the dual-thermal-fan-switch connector. Shorting all the pins together should give high speed operation. Shorting only 2 of them (you have to pick the "right" 2) will give the low speed operation. No harm in poking around, it is just ground and 2 outputs in that connector. The ground signals control 2 relays (high and low) under the dash. It is permissible to engage them simultaneously or individually.

[Seerlah]

This seems like a good place to ask.

My coolant temp gauge does not always sit in the middle, and I assumed it was because of the CTS. I replaced that, the needle rose to the middle and stayed there...so I thought. When I went driving, I noticed it still gradually dips below the middle mark. What do you think the issue could be? Depending on how much I use the throttle, the needle can sit in the middle or not. You think because of the weather? But this is the first winter I have expereinced this. I am hoping it's not the thermostat. My TB is due in roughly 20k, and wanted to do everything on one shot then. Thanks!

[Avant Nate]

This seems like a good place to ask.

My coolant temp gauge does not always sit in the middle, and I assumed it was because of the CTS. I replaced that, the needle rose to the middle and stayed there...so I thought. When I went driving, I noticed it still gradually dips below the middle mark. What do you think the issue could be? Depending on how much I use the throttle, the needle can sit in the middle or not. You think because of the weather? But this is the first winter I have expereinced this. I am hoping it's not the thermostat. My TB is due in roughly 20k, and wanted to do everything on one shot then. Thanks!

I had this problem when I changed my malfunctioning Tstat with a Stant. At Low RPMS it would stay at the middle, but at higher RPMS, such as sustained highway speeds, the temp would dip. I replaced it with a Behr, I think, and now stays in the middle. I did compare the 2 before changing it and the lip on the Stant was less pronounced. My guess was that it wasn't securely seating, at at higher RPMS the water pump was able to push coolant past the Tstat faster than it was supposed to.

And to the OP, I have my EFK wired to the low temp switch, the AC fan only comes on when really hot.

[hazard860]

is the coolant temp sensor black? if its blue then that's why its not dead middle.

[Seerlah]

Green

[hazard860]

hmmm, don't know why i though it was black but mines darkgreen too, just like this.

http://www.ecstuning.com/Audi-B5_A4-...nsor/ES278082/

i remember the dealership gave me a blue one when i got the car and it only read halfway, unless you beat on it.

[walky_talky20]

Seerlah has an '01 I believe. So he has this one:
http://www.ecstuning.com/Audi-B5_A4-...nsor/ES264174/

[SS92]

This seems like a good place to ask.

My coolant temp gauge does not always sit in the middle, and I assumed it was because of the CTS. I replaced that, the needle rose to the middle and stayed there...so I thought. When I went driving, I noticed it still gradually dips below the middle mark. What do you think the issue could be? Depending on how much I use the throttle, the needle can sit in the middle or not. You think because of the weather? But this is the first winter I have expereinced this. I am hoping it's not the thermostat. My TB is due in roughly 20k, and wanted to do everything on one shot then. Thanks!

Seerlah, I had the EXACT same problem as you. I replaced my Thermostat with a Wahler unit. Not only have my MPG's risen, but my car hits operating temp and STAYS at operating temp much much faster. I replaced my CTS with the exact one Walky listed (and I assume yours too, I have a 2000 same split VIN) and that is when it started dipping while driving. Sounds like you might be due for a thermostat change. Took me an hour and a half with a replacement and coolant flush, and I work extremely slow. I always double the amount of time people write on their DIY's for myself. Sometimes triple... :P and I might also mentioned I flushed my coolant 3 times before a refill so that may have helped some too, plus my heat is actually working now.

Unit I bought - http://www.fcpeuro.com/products/audi...r-050121113c-w

[Seerlah]

Yeah, going to order a replacment thermostat in a couple min. Going to hold off on my TB kit till later. Thanks guys!

/thread jack

[prizmatik]

Just had the chance to check out the car again. I swapped the ECT sensor out with a spare I had available. Its a different style, but plugged in. Ran the engine, temp. guage rose slowly, and when I noticed it at normal operating temperature, the oil temp. was super high. That's when I shut the engine off. I checked the lower radiator hose, and it was cold.

The ECT sensor I replaced it with is slightly different on the actual sensor side.

[prizmatik]

The electric fan has 2 speeds, high and low. Low speed is engaged whenever the a/c is on. High speed will engage if ever the a/c high-pressure switch closes.

Further, the electric fan is also controlled by the dual-thermal-fan-switch, which is completely independent of a/c operation. The Low Speed of the fan will engage if the coolant temp at the radiator outlet rises above 95C. The High Speed will engage when the outlet temp rises above 102C. If the viscous fan is operating properly, the electric fan will normally only kick on for stop and go driving with high ambient temps (in which case you usually have your a/c on anyway, giving constant low speed operation regardless).

If the car is overheating and the electric fan has not kicked on, you would want to check if the lower rad hose is hot. It is entirely possible for the lower rad hose to be stone cold while the car is overheating. This would mean either the t-stat is stuck closed (rare), the t-stat is installed backwards (not as rare), or the water pump has failed. Other possible causes could be a plugged radiator or a significant air-lock in the system that is preventing flow.

It is also possible that the coolant temp sensor or the gauge itself is lying, and the car is in fact not overheating - but that should be somewhat obvious (boiling over and what not). You can pretty easily test the fan control system via the dual-thermal-fan-switch connector. Shorting all the pins together should give high speed operation. Shorting only 2 of them (you have to pick the "right" 2) will give the low speed operation. No harm in poking around, it is just ground and 2 outputs in that connector. The ground signals control 2 relays (high and low) under the dash. It is permissible to engage them simultaneously or individually.

The lower radiator hose is cold, while the upper hose is hot. I removed the thermostat, but didnt solve the problem. I grounded the fan switch plug, and I am getting low and high speeds on from the fan. Is it my fan switch? I replaced it with a spare I had in the garage, but I suppose it could have been bad. BUT.....The lower hose is not hot. Radiator clogged? Water Pump Bad?

[rockersteady]

The lower hose is not hot. Radiator clogged? Water Pump Bad?

This would mean either the t-stat is stuck closed (rare), the t-stat is installed backwards (not as rare), or the water pump has failed. Other possible causes could be a plugged radiator or a significant air-lock in the system that is preventing flow.
.

If you have hot at top, (water circulates from cooled into lower block after being cooled by radiator, up thru the clylinder block, into head at stops at thermostat, when hot thermo opens and allows coolant to flow to radiator) and there is no flow (your thermostat is removed?) then your pump is not working, should be able to disconnect upper hose and feed slightly upward to a container- if pump works you will have coolant flowing out. Even with a partially clogged radiator you should have coolant flow, as you appear to have none I d say its your pump (the belt is attached?) or a air lock. Drain the entire system from a lower hose with last position of AC in heat mode, and refill SLOWLY from the coolant header.

whoops, I just recalled my thermostat is under my pump,
Coolant circulates from lower block to out head in all water jacket engines so Id still check for flow coming out upper hose to see pump function (when thermostat is removed of course)

[prizmatik]

I have a 1998 1.8T.....So, the coolant flows from the engine to the top radiator hose, through radiator, and out the lower hose?
I have verified the radiator is flowing well.
The waterpump belt is attached, thermostat out.

[prizmatik]

Well.....I was able to get coolant to flow from the top metal cooling line going to the upper radiator hose, but didnt seem to be as much coming out as I would expect.

[prizmatik]

Also, the oil temperature guage is fluxuating. There is definitely something going on with it. Do you think the oil cooler could be causing problems?

[rockersteady]

Just had a quick look.
The coolant is pumped from pump to lower block-( internal fitting on pump) from there it goes up the block (liners/ turbo/ cylinder head) out the back of engine and now 2 ways.

1. to heater core, out heater to oil cooler (and it acts as oil warmer too in our case:) ) and back to suction side of pump directly.
2. to the upper radiator, out lower radiator to thermostat and then suction side of pump

engine cold/ warming up phase- all coolant passes thru circuit 1.
engine approaching op temp, circuit 2 starts to open and cooling takes place in radiator.

Minimal- to no flow thru top hose when cold.
If your thermostat is removed, and circuit 2 (I presume has least resistance), you should have a reasonable flow out top hose in your case when cold.

as you said you were cautious because high oil temp when allow engine to warm up I wouldnt believe it, the coolant jacket would overheat long before your oil gets super hot.
Put your thermostat back in after checking it opens in a pan of water brought nearly to boil.

There are 2 places Ive seen the oil temp sender on a AEB. on the pan and on the oil cooler.
I really dont think you have a problem except for a dud oil temp sender?

[prizmatik]

Thanks for the info. "rockersteady". I am thinking the oil temp. sensor is bad too, but wasnt positive because of the coolant lines flowing to the oil cooler.