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-   -   How do you check your thermostat on 740i 2001 (

chuck duncan 08-29-2010 11:38 AM

How do you check your thermostat on 740i 2001
i need to verify that thernostat works..I don't want to go thru this again. I put the thermostat
housing into boiling water..nothing happened. What is the correct way to check.

HLB 09-08-2010 03:48 AM

I don't know the proper way, but thats the way I have been doing it.

balance 09-08-2010 07:27 AM

I'd guess that you need a thermostat then. I've heard that there is a material inside of thermostats that expands and contracts due to heat (wax? or spring?), and if it isn't working in boiling water, there probably wouldn't be a difference with antifreeze? But how long did you keep it in the water? Engines take some time to warm up coolant.

HLB 09-08-2010 03:00 PM

There is a spring in them. Basically as soon as you throw it in the boiling water you will see it start to open like a clam. The type of liquid won't make a difference, because it is still dependent on temperature.

CodyItaliano 09-10-2010 06:16 PM

the E38 uses an electronicly controled thermostat. it is not oporated by the use of a wax thermostatic element. and just for the record, putting an old fashioned thermostat in boiling water still does not tell you if it opens at the correct temperature. water not under pressure boils at 212 degree F. most modern thermostats are supposed to open at 182-190 degrees F. if it is opening after the correct temperature, like in depressurized conditions in a pot, thats not telling you the correct opening point. also the pot would radiate heat into the thermostat, and again is not correctly telling you anything. possibly would do more damage that way too.

sometimes a bad thermostat on BMWs will show a engine code, possibly and engine light will come on too. but not always. to test the thermostat on your E38 properly, you would need to use a scanner tool that connects under the hood. they are expensive though. the OBDII port in the car will not tell you about a faulty thermostat, just basic things, sensors and whatnot.

balance 09-10-2010 06:59 PM

Cody, that is true, but I believe that the thermostat in our cars will still open even if the harness is disconnected, and since he said that nothing at all happened when he dropped it in boiling water, I'd guessed that it was faulty. I believe the harness is connected to a heating element inside the thermostat that causes it to open early for some reason, I think I read that somewhere :dunno:.

Also, I've read on different forums that the two wires that connect to the thermostat have caused alot of engine fires in M62 equipped BMWs when they lose their plastic shielding and either connect to each other or become grounded to the motor, which is why some people leave them disconnected and wrap them up individually with black tape. So that's something else to look out for.

CodyItaliano 09-12-2010 12:16 AM

BTW the thermostat for the E38 runs about $120 for an aftermarket piece. Don't know what the run from the dealership.

PHOENIXCOUPE 09-14-2010 06:45 AM

BMW Msrp on the characteristic control thermostat is $100.56 p/n 11-53-1-436-386
let me know if you need one, I can ship for a few bucks extra.

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