Thermostat reading BLUE on highway
 

Hi, my first post here on 318ti.org.

I seem to have an issue with my thermostat, which I've really noticed since taking my 1995 318ti (M42B18 engine) to a cold winter climate after driving it solely in Miami.

While driving around town or when the car idles, the thermostat reading is normal (needle around 12 o'clock), and the car interior can heat up fine. However, when I drive on the highway for a while, the reading always drops off, and the needle sits in or on the edge of the blue. Then, the car interior doesn't heat up very well. The same thing happens with the gauge even in hot weather while highway driving. Essentially, increased air flow over the engine causes the thermostat reading to drop...I doubt the air flow is actually cooling the entire engine.

Is this a faulty thermostat? Something else with the coolant system?

Thanks in advance!

First thing to do is check your coolant level.

Faulty thermostat. It's sticking open.

Coolant level is good. Will replace thermostat.

My friend suggests that I might as well flush the coolant and replace my water pump while I'm at it...he's sure it'll eventually break. I'm at 105k miles. Thoughts?

Your issue is the thermostat being stuck open. And replacing the water pump is a perfect example of good preventative maintenance.

A Cooling system failure can destroy the engine, so spend a little now to prevent spending alot later...

Oh, and Welcome to the .org!

Come on out to meet with us this weekend in NorCal and we can swap it out together.

We're trying to get Adam to drive back from TX. :cool:

Also... 100K miles is a good point at which to replace the radiator.

Thanks for all the advice! Admittedly a little nervous to do the repair and water pump change, after reading about other people having trouble with leaks afterwards and removing seized parts. But I know it's gotta be done.

One more question, I've learned that it's the CPS sensor that runs in front of the thermostat housing (see pic attached). The sensor can be removed with a 5mm allen wrench, but then there's the plastic guide for it. Will that get in the way? It runs in front of then behind the thermostat housing.

Thanks all!

It's relatively easy to remove the CPS and simply move it out of the way while you work.