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View Full Version : coolant temp gauge takes forever to go to 90.



suju82
01-11-2010, 02:50 PM
Ok so my coolant gauge was taking forever to get up to 90 a few days ago and at some point i think i even would go down so i replaced the coolant temp sensor. The waterpump and thermostat was replace about 28000 km ago when i did the timing belt. Now the car gets up to 90 and stays there whether it's road or highway driving but the only thing is it takes between 20 to almost 40 minutes sometimes for it to get the 90. The heater is blowing warm/hot. What else could it be? I spoke to my mechanic and he said it could be the auxilary electric waterpump. Any idea where that is located? Any other suggestions as so what it could be?[headbang]

suju82
01-11-2010, 04:40 PM
Also when i took out the old CTS, there was quiet a bit of black gunk stuck to it.

dangerous_dave
01-11-2010, 04:55 PM
Did you get an oem thermostat or a Chinese/aftermarket t stat? Thermostats go bad bro.

Coopa
01-11-2010, 05:04 PM
x2^


I bought and installed 2 crappy ones before I got something decent.

suju82
01-11-2010, 06:13 PM
I had the ECS timing belt kit parts. Not cheap chinese stuff.

walky_talky20
01-11-2010, 06:59 PM
I would verify coolant temp in vag-com, but it sounds like the thermostat isn't fully closing to me.

suju82
01-11-2010, 07:32 PM
What block is it for the coolant temp and what should the temp be at? Thanx for the help.

walky_talky20
01-11-2010, 07:47 PM
You can check coolant temp in block 003, I believe. You are basically checking that the gauge and ecu agree (as the CTS is actually 2 sensors in 1). Dead center on the gauge is 90 degrees C - operating temp. So you probably want to check it when the car is cold - make sure it is reading ambient temp. Then check it after 10 minutes of driving or so. If the gauge reads cold still, but the ECU reads 80-90 ish, then the sensor is faulty. If they agree, then the coolant is *actually* cold, and it is probably the thermostat.

salz2135
01-11-2010, 08:05 PM
You can check coolant temp in block 003, I believe. You are basically checking that the gauge and ecu agree (as the CTS is actually 2 sensors in 1). Dead center on the gauge is 90 degrees C - operating temp. So you probably want to check it when the car is cold - make sure it is reading ambient temp. Then check it after 10 minutes of driving or so. If the gauge reads cold still, but the ECU reads 80-90 ish, then the sensor is faulty. If they agree, then the coolant is *actually* cold, and it is probably the thermostat.

Isn't a third option that the instrument cluster gauge is not operating correctly? In that case, I would add that you should run an output test to rule this out.

walky_talky20
01-11-2010, 08:24 PM
Isn't a third option that the instrument cluster gauge is not operating correctly? In that case, I would add that you should run an output test to rule this out.

Good one. Haven't heard of too many failures, but it sure could be.

suju82
01-11-2010, 08:34 PM
Also when i changed the CTS i let the car sit for a good 1.5 hrs and had the reservoir cap off to relieve the pressure but when i pulled out the old CTS coolant was still gushing out so i had to quickly take it out and put in the new one. Is it normal for the coolant to gush out like that even though i had let the car cool down and relieve the pressure and also is the black gunk on the CTS normal? I didn't get a chance to see if there was more inside the flange as the coolant was gushing out and i had to plug it quickly.

suju82
01-13-2010, 02:33 PM
Haven't had a chance to log the car yet but just wanted to confirm something. Once you've driven the car for like 30 minutes and the needle is upto 90, shouldn't the upper coolant hose be piping hot that you can't hold on to it for more than a couple seconds? I'm talking about the rubber portion that connects the rad to the rest of the metal pipe coming out of the engine.

Mine is hot but not piping hot. Can someone verify this for me? I've timed exactly how long it takes for it to get to 90 for the past few days and it's about 13-15 minutes.

Lou_B5
01-13-2010, 07:00 PM
Sounds like you are in the same boat as me. It only gets to operating temp when I let the car idle. But when I drive, it starts to cool down slowly.

Is this what is happening to you?

I just changed the therm as well so it must be a bad one or posible air in the system. cts is perfectly fine.

suju82
01-13-2010, 08:23 PM
well before i changed the CTS i noticed the temp did go down once but since replacing the CTS the needle doesn't go down just takes a long time to get to 90. It was taking 25 min or more for a couple days and then the last couple days it was taking 15 min but then today again it took over 20 mins. I'm going to replace the thermostat and see what happens. Did replacing the thermostat fix the problem for you or are you still having the same issue? Or did you mean you are having the same issue as me and you've recently changed your thermostat?

Lou_B5
01-14-2010, 04:47 AM
No I changed the therm as preventive maintenance only to run into this issue.

suju82
01-14-2010, 07:37 AM
Just picked up a jug of coolant and new thermostat with o-ring. Will flush and replace tomorrow. I saw the DIY but i think my thermostat is on the bottom right since it's an aeb motor and the DIY was for the newer b6 1.8t. When i flush and refill the coolant does it matter if the car is flat or on an incline? When we did my timing belt and stuff for some reason the car wouldn't start and i had to get it towed to the mechanic and when it got there and my mechanic started it, it started right up. I think when the car for moved around the bubble came up and i believe there's a plug on the driver side of the rad that's a coolant sensor (not coolant temp sensor) and that's why the car wasn't starting that time cuz it wasn't sensing coolant as the driveway was uphill(a good 20-30 degrees incline). Can someone confirm that plug is the coolant sensor and that's what the problem would have been so i don't run into the same problem again? Also when on the DIY it said to fill new coolant and run heat on high and refill reservoir when the level goes down. Should i keep the cap on or off while i'm waiting for the car to warmup after changing the coolant?

walky_talky20
01-14-2010, 09:04 AM
The plug on the lower left side of the radiator (driver side) is not a temp sensor. It is a dual thermal fan switch. It is merely to control the secondary (electric) fan during overheat conditions. This switch has no input to the Engine Computer and should not effect the engine starting. But, if the coolant temp sensor in the back of the head wasn't touching coolant, that may cause issues. Issues that could be corrected by simply waiting, or burping the system or what have you. I wouldn't worry about it.

After you refill the coolant, you can leave the cap off and open the coolant bleed hole on the heater core hose. It should let some air out as the engine runs for a bit. Once you see coolant coming out steadily, re-clamp the heater core hose and put the cap back on the expansion tank.

suju82
01-14-2010, 08:30 PM
where on the heater core hose is the bleeder screw located? Is if in the engine bay area or in the battery area? Thanx for all the help.

walky_talky20
01-14-2010, 08:35 PM
Heater core hoses are inside a plastic accordion style cover beside the battery. One of them has a small hole in the top of the hose that is exposed if you unclamp it and slide the hose back a bit. This document has instructions on the official coolant refill procedure, including the bleed hole and stuff;

http://www.pvv.org/~shane/stasj/pics/motor/dokumentasjon/A4-S4_B5/Engine%20Mechanical/1.8T%25205V%2520(AEB%2520&%2520ATW)/Engine/19-1%20Cooling%20system%20components.pdf

suju82
01-15-2010, 12:34 PM
Just replaced the thermostat and all is back to normal. Thanx for all the help everyone. Especially walkytalky.