View Full Version : Thermostat issue?
Last night on my six mile drive to pick up pizza, I stop at a light and while idling I notice my tach oscillating just a hair. Nothing I could hear, just a visual needle thing. Never noticed it doing this before.
A minute later as I am driving again, I look at the temp gauge and notice it is sitting in this position:
http://farm5.static.flickr.com/4033/4641449699_789aed5519_o.jpg
Again, this is well after the normal engine warm-up time frame and the car is running fine. Then while I am staring right at it, it moves up to normal (vertical) within 2-3 seconds - like I reached over and set it with a knob. It stayed there the rest of the way home.
Idea?
4everRS
May 26th, 2010, 16:11
Mine did this last fall. After a new T-stat with 75k service it hasn't happened again.
The T-stat can fail slowly. Have you ever seen a CEL for the cooling system? How is your radiator cooling fan running?
Never a CEL and fan operation seems normal. Everything involved with the cooling system acts as if it's normal. If I didn't happen to visually see the gauge at the time I did, I would never have known it did anything strange.
4everRS
May 26th, 2010, 17:08
I guess I would just watch it. Like I said, mine did this and it didn't throw a code right away. Later on, I got a CEl on the cooling system. The fans ran wide open as well, but again it was after a while. Just keep an eye on the guage and the possiblilty of a CEL.
These cars can be so goofy sometimes. Well worth it though.
Never a CEL and fan operation seems normal. Everything involved with the cooling system acts as if it's normal. If I didn't happen to visually see the gauge at the time I did, I would never have known it did anything strange.
Gustaf
May 26th, 2010, 22:07
On my A6 4.2, I once saw the gauge go past normal and stay there. I had recently done a timing belt service with a new t-stat as well so I stopped the car, turned it off and immediately turned on the ignition again. Sure enough the gauge was now showing normal...gremlins.
DHall1
May 26th, 2010, 22:35
It must be good pizza.
Last night on my six mile drive to pick up pizza, I stop at a light and while idling I notice my tach oscillating just a hair. Nothing I could hear, just a visual needle thing. Never noticed it doing this before.
A minute later as I am driving again, I look at the temp gauge and notice it is sitting in this position:
http://farm5.static.flickr.com/4033/4641449699_789aed5519_o.jpg
Again, this is well after the normal engine warm-up time frame and the car is running fine. Then while I am staring right at it, it moves up to normal (vertical) within 2-3 seconds - like I reached over and set it with a knob. It stayed there the rest of the way home.
Idea?
It must be good pizza.
Pittsburg style - worth the drive!
V8weight
May 27th, 2010, 01:12
Scott, be on the lookout for a coolant leak. Once the car reaches operating temp, the thermostat opens and stays open, there's no way for the car to lose that kind of coolant temp. I think what's happening is there is a small leak somewhere, and air is displacing the coolant. When you're idling, there is a reduction of coolant flow, and the air finds it's way to the highest point in the cooling system (which happens to be the coolant temp sensor). When you start driving, the increased rpm pushes the air bubble back into the system and the temp sensor is reintroduced to the actual coolant, thus the sudden increase in temp. This was my experience when my after run coolant pump failed. I had about two weeks of your exact coolant temp fluctuations, then it finally started showing signs of a leak in the garage. If you get under the car and look, there will be coolant running down the bell housing if the pump is leaking. Just a theory, don't let my babbling ruin your day.
Thanks for that tip. I will put it up tomorrow and take a look!
DHall1
May 27th, 2010, 05:31
+1
Thermostat can stick open or closed.
Sticks open and the car takes forever to reach operating temp.
Sticks closed and the car overheats.
Now, on your 6 mile drive for pizza...good pizza....you could have a situation where the thermostat opens and then stays hung open for a period. The coolant temp will drop alittle but not drastic. I think your picture is drastic. If tstat was hanging closed you would see a spike up in temps.
So, the air bubble situation is possible as is the tstat sticking open. But from the looks of the extreme drop in temp....I vote air bubble 70%.
Scott, be on the lookout for a coolant leak. Once the car reaches operating temp, the thermostat opens and stays open, there's no way for the car to lose that kind of coolant temp. I think what's happening is there is a small leak somewhere, and air is displacing the coolant. When you're idling, there is a reduction of coolant flow, and the air finds it's way to the highest point in the cooling system (which happens to be the coolant temp sensor). When you start driving, the increased rpm pushes the air bubble back into the system and the temp sensor is reintroduced to the actual coolant, thus the sudden increase in temp. This was my experience when my after run coolant pump failed. I had about two weeks of your exact coolant temp fluctuations, then it finally started showing signs of a leak in the garage. If you get under the car and look, there will be coolant running down the bell housing if the pump is leaking. Just a theory, don't let my babbling ruin your day.
I honestly don't know if the engine ever warmed up to normal before I happened to see the location I posted above.
It may not have "dropped" there. I'm thinking it may have been stuck there. Will know later today hopefully.
Possibly a temp sending unitor sensor? Anyone know where this might be located?
4everRS
May 27th, 2010, 17:36
Sending unit will be in the back of the motor in the coolant pipe. Should have either a black (stock) plastic area where the plug goes, or a green one witch is the updated and more reliable version.
Possibly a temp sending unitor sensor? Anyone know where this might be located?
Appreciate it. I forgot, I have EKTA to look at! ;)
*5 mins later*
Found it. Says it's green - #059919501A
Looks easy enough to swap out...time to order one and see what happens.
Mine just started doing the same thing today, hoping its the temp sensor.
Did you have any luck with the replacement?