Hello!

I recently bought myself a A4 1.8T 1999 and there is something wrong with coolant temp. When i drive on a straight line temp never goes over 75c. And when i am driving downhill some time the temp decreases to bottom line(60c), When the car is in idle the temp increases to normal temps. and last if i stop the engine when it shows 75c and start it again in a couple of minutes the temp is higher, like 90c.

Can anyone help me with this? i tried to change the coolant temperature sensor, didnt make much of a change, one thing i noticed though, the old sensor was green colored and the new one was blue. did i get the wrong one then? I havent got any warning light or error codes btw.

 

Check your coolant level and test your sending unit. If the sending unit is good, replace the thermostat, flush the radiator and refill.

I believe that should do it.

 

I can't help but wonder if the last guy left a bubble in there. Those are real bubble symptoms, esp the part about how the temp changes downhill. Look around you'll find a lot of talk about hiw you give that motor a food healthy belch.

 

At a guess, I would say the Thermostat. I had similar problems on mine when I bought it and it was the Thermostat. When the thermostat fails on these cars, it fails in the open position unlike some other cars. You can google some info about how to check it but once I changed mine, it warmed up a hell of a lot quicker and got to operating temp and stays there regardless of how you drive instead of running cool.

 

That's interesting - and really good to know!

 

I think it's better! Instead of closing and cooking your car, it remains open. The only downside is the car runs cooler instead of at operating temp. but that's 100 times better than running hot!

 

Hell yeah!

I'll take that over the "pressurized 'till something explodes" problems associated with sticking closed any day.

Besides: I'm in Florida. That would probably help down here. lol

Again: great info! Thanks.

 

Doesn't sound like the thermostat at all. Never heard of it acting like that. I drove around with a busted thermostat for a week or so and it never acted like that it just would never get up to normal operating temp.

Sounds like a bubble like someone already said.

 

I completely disagree. When the tstat goes bad, it sticks open and keeps circulating coolant. At idle, it will read normal temp since the water pump is not moving that much coolant. however, at speed, the temp will go down since the pump moves the coolant faster and it cools off much more. normally, the tstat closes until the coolant gets warm enough to open it.

 

I know how it works. I just went through the problem last month and mine did not act like that at all. It would never get to operating temp it would move up very very slowly but it would never move back and forth. First time I've heard that and I did a lot of research on a bad tstat before I replaced mine. Could be though, easy enough part to replace. The coolant is actually more than the part.