Engine temp fluctuating between normal and hot

[05UltraSprt]

Good morning all,

I did a search, but didn't find anything definitive. Yesterday, the temp gauge starting rising, stopped at about the 3/4 mark. Stayed there for a minute or so, then dropped back down to normal operating temp. Five or ten minutes later, same thing. Five minutes after that, same thing, but the temp made it a little higher on the gauge. That's it. Every time it starts to rise again, it goes a little higher. It stays hot for a few minutes, and then it goes back down.

Checked the fluid - It's full
Checked for codes - I have one, for a MAF, but it's been there for a week or so (haven’t gotten around to ordering one yet)
Checked for leaks - nothing I can see.
Fans seem to be working fine.

First thing that comes to mind is a sticky thermostat, just wanted a second, third, fourth and fifth opinion.

Any help would be greatly appreciated.

TIA

[manguyen]

this happened to me once... it was a thermostat. it got hot when i was parked and went back to normal when i started driving.

[3thrd_a_4]

Coolant temp sensor.

[dougyfresh]

Have you replaced the coolant temperature sensor in the back of the cylinder head?

If so, then my next guess would be the thermostat.
Here is some info on the thermostat: http://audizine.com/forum/showthread...38#post2438838

[manguyen]

BTW if its your coolant temp sensor, audi will replace for free!!!

[05UltraSprt]

Replaced coolant temp sensor & thermostat this weeend, still having the same problem. Anybody happen to have any other ideas??? The system builds pressure as intended, the fans turn on as intended. I should note that I have not changed the coolant temp sensor in front, only the one near the firewall. I guess I'll try that next. Maybe I'll just drop it off at Audi tomorrow and let them deal with it.

Anyway, any other suggestions would be appreciated...... Thanks.

[gtimart]

I always tought fluctiating temperatures were because of an air bubble inside the system. Could that be happening here ?

[dougyfresh]

Did you purge the air from the system? there is a bleed screw on the upper radiator hose hard line (ontop of your intake).

[05UltraSprt]

My coolant slowly leaks from that screw - Cheap ass platic thing. So, I'm going to assume becuase I see water coming from there, it's bled.

On a side note, isn't there a metal replacement screw available for that bleed valve?

[dougyfresh]

I'm fairly sure the bleed screw on my car is metal. It never leaks. There's a copper washer. Perhaps replace that first?

[05UltraSprt]

For those that may have been wondering what the problem was....



....and that's at 71K miles.

[F16HTON]

72K miles is pretty good for the water pump...

[05UltraSprt]

Yeah, I guess I learned that the hard way...

Had I known, I would have done the pump and the belt 10K miles ago.

[My OOOO My]

Coolant temp sensor.

x2.... absolutely

Ooooppppsss..... I didn't see your pic of the broken water pump.

[drmarcj]

Plastic impellers? Seems like a good case for getting the upgraded metal impeller type that is out there (see ECS Tuning website)

[05UltraSprt]

Plastic impellers? Seems like a good case for getting the upgraded metal impeller type that is out there (see ECS Tuning website)

Yes, stock pump has a plastic impeller (POS). ECS Ultimate kit is in there now, along with a few other ECS goodies...