Thermostat Replacement

[White Z]

Well driving the car in the cold weather isn't the best idea I've found out. Today I went for a drive and it was about 12 degrees. After about a mile the temperature gauge went from cold straight to hot and the engine light came on. The car did not overheat (Thank God). I was able to drive it home since again it was just about a mile from the house. I believe the electric thermostat might be stuck open. I'm going to replace it and I was wondering since I have to remove a lot of stuff should I do the water pump, belts and hoses since everything is off. The car has 87000 miles on it and everything appears original. I.e. 20 years old.. thanks.

[jclausen]

It's stuck closed if it was stuck open your engine temp gauge would probably read 1/4 of so instead of 1/2, any way if the water pump, belts, hoses are old certainly go ahead if your budget only allows stat and hoses ok, remember to bleed the coolant system when done

[White Z]

Sorry, stuck closed.

[rf900rkw]

>After about a mile the temperature gauge went from cold straight to hot and the engine light came on.

>The car did not overheat (Thank God).

These statements are contradictory. Both can not be true at the same time. Several thoughts come to mind. Why are you blaming the thermostat? Even a stuck closed thermostat should take many miles before it runs hot. Does it have coolant in it? Is the coolant not just water?

Step one would be to read the codes.

[Mark Bielick]

I'd bet its a bad temperature sending unit. Shorted out, telling the vehicle the car is hot, and causing the gage to register hot. Did the car show any symptoms of running hot?

[White Z]

The car didn't show any symptoms of running hot at all. The gauge just went from cold to hot. The OBD came me a P0125 code. P0125: Insufficient Coolant Temperature for Closed Loop Fuel Control. I cleared the code and the engine light went out. I just assumed the thermostat become stuck.

[z3forlife]

My old 99 2.3 did this once. Shortly after starting to drive my temp gauge went from 1/4 to full hot with the light on and it scared the shite out of me. I quickly pulled over and shut it down. Upon restart it was normal. Luckily it never happened suddenly like that again. Does yours continue to do it when you let it warm up ?

[White Z]

I ran it in the driveway for about 15 minutes from cold and it only went up a little (still in the blue). Turned it off foe awhile thorn about 10 minutes later I drove it up the street let it sit and run and it went to hot. Doesn't overheat though.

[pepz]

I ran it in the driveway for about 15 minutes from cold and it only went up a little (still in the blue). Turned it off foe awhile thorn about 10 minutes later I drove it up the street let it sit and run and it went to hot. Doesn't overheat though.

My car did this 3 years ago when it was cold out. I just pulled over and restarted the car. The gauge acted normally after restarting but never went to the middle of the temp range. If I warmed up the car for 15 minutes in the driveway the gauge would come up slowly, but never in the middle as you mentioned. I thought the thermostat was stuck closed when just taking off in the cold. The following spring, I did a coolant refresh (including new thermostat) and the problem never happened again. To me, it appeared to be a stuck thermostat.

[z3forlife]

Is the electric fan coming on ? I assume you’ve verified coolant level is full. What year is your car

[colb]

Might be an idea to carry out an instrument test using the hidden test menu in the dashboard, it will test the temp guage to see if it functions correctly. Details on how to access here http://forums.bimmerforums.com/forum...ghlight=hidden

You can also select a digital readout of the temp you can monitor when driving.

The symptoms you have seem to point to a bad temp sensor, they are not expensive to change so worth trying first.

If the car is running correctly the temp guage when car is up to temp should be at the 12 o'clock position and remain rock steady, if the heat rises then the fan should cut in to keep it in the middle.

Thermostats usually fail in the open position causing the car to run cool, rare if yours has failed closed but not unheard of.

[White Z]

Looks like i'll replace the sensor first. It takes a really long time to get heat inside the cabin. It doesn't help that it is very cold outside also. I don't know when the coolant was ever flushed or how old it is. The previous owner had no manuals for the car repair or maintenance schedule notes when I bought it.
I started a schedule last summer with oil, plugs and all the filters. I guess this spring I'll start on the coolant side. I was just looking for a quick ride through the mountains again but it's going to have to wait.
As far as the question of the age of the car: 2000 Z3 Roadster

[White Z]

So I was looking in the Bentley manual to find where the ECT sensor is for this car (2000 z3 roadster m52tu engine). Let me make sure I have this right. I need to remove the intake manifold, fuel rail, injectors and numerous hoses and wires to get to the sensor.
Please tell me there is an easier way? Thanks for all the help.
I wonder if Ant from "Wheelers Dealers" has some free time.

[jclausen]

Get an infrared heat gun and read the coolant hoses

[Vintage42]

... If the car is running correctly the temp guage when car is up to temp should be at the 12 o'clock position and remain rock steady, if the heat rises then the fan should cut in to keep it in the middle...

You can't tell the temperature from the needle. The ECU is programmed to hold the needle at 12:00 from 170F to somewhere over 220F.
I have a digital guage on my console and no belt fan. The running temperature of my new BMW thermostat is steady around 207F. Before that the running temperature fluctuated between 170F and 195F depending on ambient temperature and driving conditions, indicating a bad thermostat.
The electric fan activates around 212F in summer idling. I don't know what temperature it takes to move the needle past 12:00 (but I read that it is over 220F), or what the temperature is in the red zone.

[White Z]

Well I was doing some thinking and I think I'm going to start collecting parts to do a complete coolant refresh. I watched some videos from Paul Schroyer (same car and m52tu engine) on YouTube. From what it looks like ill put the car up for a few weeks, collect the parts for the refresh and clean it up.
I like the idea of the Stewart waterpump (especially the warranty). I didn't notice if he replaced the coolant sensor on the block though. I'm not sure I want to replace the radiator can't understand why I should and not sure if I should put in an electric fan. I like the idea of replacing a lot of the corroded plastic parts. Any ideas?..