meem

folks,

about two weeks ago, i was driving down the highway at a leisurely 70 or so and noticed that my water temperature gauge was on "C" instead of in the middle where it should be. i pulled over, restarted the car, and boom, it went right back up to the middle.

since that time, the situation has been getting worse. first, it would fluctuate between "C" and the correct value in the middle. now it generally just sits on "C" but can often be coaxed back up to a correct value, either by restarting the car (which for some reason often fixes it) or by just remaining parked for a few minutes.

during this time i haven't noticed any other odd behavior, and i have not seen any frighteningly high values that would cause me to think that the temperature sensor itself has gone bad (for instance, it's not like when it works it's pegged on "H").

since i'm scheduled to go in for service soon anyway, i was going to let me dealer try to figure it out. however, since it's intermittent, it's going to be hard for them to track down, and in any case i don't want to end up like jyoteen.

does anyone have any thoughts about what might be going on? btw, just for kicks, i swapped back in my stock ecu, and that didn't change anything (in case someone thought it might be related).<p>--
meem

Adam T

I was driving just 10 minutes ago. Thought I would see how she ran after an oil change and a new F-hose. I was thinking, "Ah, cool weather, the car is running well." I take a glance at my water temp guage and it reads a big fat "C". WTF! It is always pointed straight up. I stop at a light and all of a sudden it starts to creep up to normal temps. Soon after it reads Cold again.

I was just working on the F-hose and wondered if I knocked the temp sensor loose. Where is the sensor located? I hope Bentley knows.

Adam T

Adam T

I checked with Bentley. The the Engine Coolant Temperature sensor is located behind the passenger's side cylinder head underneath the big black ribbed air hose. The (gray) connector was secure, and I am not picking any DTC's.

Adam

meem

please let me know if you track this down. it's interesting to note (now that i think about it) that i think i started seeing this problem around the same time i swapped tbb's. hard for me to remember, though..<p>--
meem

frank

sounds like your thermostat is stuck open to me

meem

<p>--
meem

frank

the spring rate is chosen to keep it closed until the pressure from the coolant forces it to open (pressure increases with temp.) Now the thermostat is generally inside of the short pipe going form the engine block to the top hole in the back side of the radiator. it stays closed until the water trapped inside the engine block hits about "boiling" (210F or 100C) and this allows your engine to get up to temperature quicker than if it had to heat up all 6 quarts or whatever the capacity of the radiator is.

since there's probably only a quart or 2 trapped in the block. NOW if that thing gets stuck CLOSED, WELL then your engine will over heat and burst the hose and/or heat warp the cylinder heads. This would be bad obviously.

If on the other hand it is stuck open you will get the symptons you've been describing. car doesn't warm up unless your idleing or sitting in traffic
and as soon as you get air flowing over the radiator and the increase in engine revs starts spinning the water pump faster, your temp gauge goes back to Cold.

it's a lot better than warping the heads, but you'll get crappy gas mileage and probably weaker performance. Plus I think theres a small chance that you could see increased cylinder wall/piston ring wear and tear.

stuck thermostat is usually no biggie if you get it looked at SOON.

I had the same thing happen to my 97 M3 and everything was fine when the dealer changed it.

Hope this helps