I've tried to search to find the answer(s) to the issue with my car, but I'm having trouble discerning the diagnosis. I'm unsure wether to look at the coolant temp sensor, thermostat, water pump or all 3. So I'll apologize in advance b/c it seems this has been answered a time or two before.

It's an '05 B6 1.8t, 52K, owned for 5yrs almost to the date. Wife was coming home from appt when the high temp warning display came on and temp was in the red after 5min from a relatively cold start (car was idle for 3hrs). She drove another 5min home where it stayed in the red. Sat another 3hrs til I got home. Coolant level was fine.

Took a short drive, climate off, temp gauge was at zero, but began climbing quickly after 2blocks until it leveled at the 1/2 way mark. Stayed there for another 1/2mile, then quickly climbed to the 3/4mark and the high temp warning light came on. Stayed until I pulled into driveway.

Let sit 1hr, restarted and temp was at 1/4, turned climate to "HI" with fan full, drove and temp again stablized at 1/2 for a few blocks then climbed up to the red along with the high temp warning. Drove home, in driveway it lowered to 3/4 or just below. Turned off then restarted car, idled for a few seconds, temp gauge was dropping to just over half when the high temp warning came on.

With the climate to "HI", the air felt cold at first but began heating up by the time I got home (5min tops). It never felt super warm but it was also almost 90 outside which is warm for us.

Thanks in advance for anyone who can shed some light on this.

 

I can think of a few possible cauese:

1. Bad thermostat
2. Clogged or obstructed radiator
3. Clogged or kinked radiator hose
4. Blown head gasket

I'm sure others can come up with some also. T-stat is cheap, the others not so much.

 

Thanks for the reply. Is it more likely a tstat over the coolant temp sensor?

THis morning when it was idle overnight, within 1 minute, the temp reading shot up to 1/2way, sat there for 4 or 5min, then shot up to the red. Is that even enough time for a car to overheat even assuming it was a bad water pump?

 

Time to troubleshoot. You need to determine the actual coolant temperature, and measure the resistance of the sensor as the car warms up.

A laser temperature sensor would be ideal for coolant temp. Someone should have the reistance curve for the sensor - put an ohm meter on the sensor and record the readings.

 

Thanks for the reply. Here's an update, I replaced the coolant temp sensor just because it was cheap and (relatively) easy. I haven't had to turn a wrench in years, so I went ahead and had it towed to a shop. Bad thermostat, which was replaced. Water pump is also bad which will be replaced.

Service rep is telling me though that it's very likely there's damage to the motor b/c it was driven while overheated. It was driven for roughly 5min overheated. Is this really enough time to do some damage? Service rep says it can ruin a motor in a matter of minutes, but I'm wary of that. There was coolant in the system which is different than overheating while dry. I realize it's an aluminum block and head, but is there really that great of a chance that the motor's bad?

 

So water pump and timing belt are in; seems to run good and doesn't overheat. I had a different shop do the water pump and timing belt than the one who did the thermostat. This shop says it's a possibility the there's damage, but told me just to drive it and keep an eye on the coolant level for a while. The fact that it starts, runs fine, and no CELs is a good sign. Anyone have some more imput on whether I should have something to worry about or longevity perhaps?

 

I vote for water pump. Had a similar problem, and the water pump was the culprit (cheap plastic impeller split).