So I've been having this problem lately that my engine never seems to come up to full temp. After several suggestions I went ahead and replaced the coolant temp sensor with a new one. This did absolutely nothing and I'm still left with a motor that only warms up 2/3 of the way.

So I was driving last night out to WVU and I kept noticing how much the temp gauge was fluctuating. The whole trip for me is just over 3.5hrs and when I first started the weather was about 45°F and the motor went to its normal (lately) spot up to the second mark above cold. It stayed there without moving for the first 45mins or so. As I keep driving I notice that it has started to move back up to the center mark and see the temp outside is up to 50°F. Well after another hour or so the gauge just starts moving in around wildly. It goes from the second mark to cold and back then to the first mark and keeps jumping around. Now the movements themselves aren't wild but the readings seem to be. At one point about 3hrs into the trip while it is 65°F outside the gauge reads that its cold?!?!

I went ahead and took a picture because I couldn't believe it.

This picture was taken after driving at 70-90mph for 3hrs!

So I have no idea what is causing this nor a solution. Can someone help me out here? Its the same 01 1.8T as in the sig.

Thanks for any suggestions!

 

thermostat is stuck open.

 

I second that thought; sounds like a stuck-open thermostat. My old (beloved) Volvo had the exact same thing happen one fine winter. The engine wouldn't get off the "C" mark in weather colder than 40 degrees, and (of course) I had no heat to go along with it. Brrrr!

 

But if it were a stuck open thermostat I would think it would never warm up to temp as much as it does. I mean after 5mins of running it through my neighborhood each morning its up to the second mark and it just doesn't go higher.

How hard is it to replace the thermostat on the 01? Isn't it an internal waterpump that would make it a pita to get to? The previous owner just had the timing belt replaced before I bought it but they didn't replace the thermostat. It was done at 42k miles and I now have 57k.

 

Does your heater work?

 

Yup works perfectly. Thats it, I haven't noticed anything acting odd except the temp and poor gas mileage.

 

Gauge may be off, cause usually the heater will blow cold with the "engine temp" that low.
Some OBDII scanners can tell engine temp, or there is the option of an aftermarket gauge, or one of those little laser guys that you point at the motor to find out the heat.