Thermostat?

[widgget]

i've got an odd one. didn't find the same symptoms in any other threads.

basically after changing my oil the other day i had moved the coolant res so that i could get to the oil filter from the top, when i put it back i forgot to reconnect the sensor so i got a coolant warning. well i figured it out and plugged it back in and the warning went away. well i went somewhere yesterday and my heat woudl not warm up, it was warmer then outside but it was still quite chilly. the temp gauge went from cold to pointing exactly at the middle just like normal but the heat still never warmed up except very slightly when i brought it to 3.5k rpm after stopping at a stop sign. when i opened the hood there was gurgling noise, the coolant res had more in it then it did the night before (past max level now) and loosened the cap to release the pressure it just started spitting boiling coolant (not at me, don't worry).

so this is what i have:
no heat
boiling coolant
temp gauge shows normal operation
was just playing around under the hood (likely my fault it's not working)

due to the excess coolant and lake of heat i am assuming that the thermostat is stuck closed and that the second half of the coolant system is empty. why woudl my temp gauge read normal though and no cel's come on?
If anyone has any thoughts that woudl be cool, otherwise i'm going to order a new thermostat tomorrow.

[widgget]

well, nevermind for now, it just started working again on it's own, guess i'll wait until it stats up again.

[vee-r-six]

wait! my car does this same thing. It drives me crazy. I idled the car and looked for over 30 minutes and can't find a leak. Would a bad thermostat do this? it doesn't overheat like most cars do when the thermostat sticks shut.

[JMRQuattro]

same problem here. I had John (diagnosticator) come over and help me with it, we bled the air from the coolant lines after i had done a coolant flush, and it helped. The heater worked and got very hot for like 2 days. Now i'm back to the same problem i had before. I think i have a leak somewhere because it's been about a week and a half and my coolant reservoir is building up pressure in it again.

[vee-r-six]

If you find out what it is first let me know. Im going nuts with this thing.

[absolutegtr]

I had John (diagnosticator) come over and help me with it,

I thought he was a robot

[JMRQuattro]

^^ well what worked initially for me was bleeding the air from the lines after i flushed my heater core. But i'm pretty sure i'm getting more air in there again cause it's back to being a pain in the ass again. It really sucks, cause times like this morning when it's 28 degrees and i have to drive to school all my car will do is blow cold air

[JMRQuattro]

I thought he was a robot

haha, he's a really smart guy.

[widgget]

old guy said it was likely air in the system and i have to agree with him. try bleeding it off.

[JMRQuattro]

^^ i don't know what else to do now. I bled the air again today and it's still not helping my heat problem. One hose is still cold and the other is hot.

[widgget]

^^ i don't know what else to do now. I bled the air again today and it's still not helping my heat problem. One hose is still cold and the other is hot.

in your situation though if one hose is hot and the other cold then something between the two is closed (the thermostat).
it could be the thermostat but i don't understand why the engine doesn't overheat if that is the case, which was the reason for this post, my symptoms didn't seem to fit typical stuck thermostat symptoms that i have seen in the past.

[JMRQuattro]

^^ well my question is where is the thermostat? Because the hoses i'm referencing to are the heater core hoses that go into the firewall.

[widgget]

the thermostat is in front of the engine behind the belts (next to the water pump if you know where that is) from what i have heard. i think the timing belt can stay in place but you have to remove the accessory belt. it's a special thermostat which is controlled by the ecu, not just a spring valve like all the others i have seen. priced out on ecstuning you looking at $105 for the thermostat and $45 for 4 letters of G12 to refill the system after you replace the part.

[A4 Moda]

Time to replace the thermostat.

Do you hear your fan turning on for no reason? If so, yes thermostat is definitely gone.

Replace ASAp. if your thermostat isn't opening, that's going to be a problem.

GL

[JMRQuattro]

^^ well my biggest concern about it probably being the thermostat is that both of my fans come on in about a couple minutes even when the car is not warm yet, and my cars temperature guage inside stays at cold unless i let it idle for like 20 minutes. Even then it only starts to go up slowly and at idle alone it will not go past a quarter unless i idle it for a really long time. So usually i'll come out and it will have been 10 minutes and the car is still at cold. It only goes up to half way once i start driving the car. Along with the other symptoms of my heater being such a fuss.

[Audi Skate Snow]

i believe the coolant temp sensor will make fans go on as well.

[JMRQuattro]

how can i tell by looking at the parts if they are going bad? Because i've gotta do something to figure this out. Cause it's getting colder and i'm gonna need those things to work.

[widgget]

**not speaking from experience here, just trying to use some common sence about how things might work:

being that the thermostat is electrically controlled if the sensor is not functioning correctly the thermostat might be fine but just never getting a single from the ECU to open.

I think your just going to have to try replacing the parts. sensor woudl prob be a good place to start, don't know the cost of it compared to the thermostat but keep in mind that you will need to replace the coolant (about $45) with ether part, so if you replace the sensor and then fill it back up and that turns out to not be the issue you will need to get another 4 leters of coolant to replace the thermostat, so it might be best to just do both parts at once.

[old guy]

^^ well my biggest concern about it probably being the thermostat is that both of my fans come on in about a couple minutes even when the car is not warm yet, and my cars temperature guage inside stays at cold unless i let it idle for like 20 minutes. Even then it only starts to go up slowly and at idle alone it will not go past a quarter unless i idle it for a really long time. So usually i'll come out and it will have been 10 minutes and the car is still at cold. It only goes up to half way once i start driving the car. Along with the other symptoms of my heater being such a fuss.

Sounds to me that your problem may be with you fan control module.
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[old guy]

**not speaking from experience here, just trying to use some common sence about how things might work:

being that the thermostat is electrically controlled if the sensor is not functioning correctly the thermostat might be fine but just never getting a single from the ECU to open.

I think your just going to have to try replacing the parts. sensor woudl prob be a good place to start, don't know the cost of it compared to the thermostat but keep in mind that you will need to replace the coolant (about $45) with ether part, so if you replace the sensor and then fill it back up and that turns out to not be the issue you will need to get another 4 leters of coolant to replace the thermostat, so it might be best to just do both parts at once.

The thermostat is not electronically operated. It is a MAP thermostat that is basically a standard thermostat the can be forced to open by a axillary heating element that is controlled by the ECU.Clicky click
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[widgget]

:( "you must spread some reputation around before giving it to old guy again"

[old guy]

:( "you must spread some reputation around before giving it to old guy again"

Glad to help. Thanks for the rep points!

[JMRQuattro]

The thermostat is not electronically operated. It is a MAP thermostat that is basically a standard thermostat the can be forced to open by a axillary heating element that is controlled by the ECU.Clicky click
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damn old guy, where do you get this stuff from? That's pretty helpful. Thanks for the link!

Also, could it be that maybe my thermostat is malfunctioning in a way where it's always sending too much coolant through at all times? Cause that would seem reasonable as to why my engine doesn't heat up quickly like it should when it's cold. And could that effect my fans as well and explain why they turn on when the engine is cold?

[old guy]

Have you been able to check to see if you are getting any DTC's? I don't think the thermostat would cause to fans to come on when the car isn't up to temperature. The fans are turned on and off by the fan control module. Temperature input comes from several areas. There is the green (G62) sensor at the back of the motor that has a history of failing clicky click and there is another sensor in the lower radiator that also provide temperature information. I believe that one is referred to as a G2. Not positive of the description. If either of these sensors are defective it can cause the fans to cut on prematurely. I was working with someone else with the same issues last year. He replaced both sensors and the problem persisted. His problem ended up being the fan control module. First thing I would suggest is checking to see if you have any DTC's to help narrow down the problem.

Good lock!

[JMRQuattro]

Nope, i got nothing. I had a code for cylinder 2 misfire, but that problem was solved when i replaced my spark plugs. Otherwise i had diagnosticator check with his vag-com connector and there was nothing heater, thermostat, or sensor related being logged.

[old guy]

Are you still having to add coolant? you mentioned earlier that you improved you heat by getting air out of the system. Have you felt around the rear coolant flange on the back of the motor for leaks? That is a fairly common problem and could be causing you to get air back in the system thus no heat. however that doesn't account for the fans running when the motor isn't up to temperature. One thing you can try is to disconnect the sensor in the lower radiator hose before a cold start and see if the fans still cut on too soon. If it has no effect and the fans still run when cold I would lean toward the fan control module. Clicky click The DIY is for a 3.0 but the 1.8T is very similar.

Good luck!

[JMRQuattro]

well i just added in more not too long ago after i did a coolant flush and i haven't been driving my car since i went to colorado. And i fixed a leak that i had because of a bad hose clamp so it's been better but i still don't know for sure how much better it is. But i'll try unplugging the sensors and seeing what happens.

I have a couple things to do on my list so i'll probably hit them all at once. But i just got my season's pass for snowboarding in the mail, and i just saw the new warren miller, so i hope i can fix whatever is wrong with my heater soon. Or else this is gonna be a cold winter...

[old guy]

Edited my response above. I meant to say try disconnecting the sensor in the lower radiator hose. That one that has a direct effect on the fan control module.

Again, Good Luck!