Thermostat Question

Hello,

My 2008 328i sedan all of a sudden had its engine service soon light on. I was hesitant to take it to the dealership since my warranty and extended maintenance place has expired. Well, anyways i did take it to get it checked up. Initially, when they put the key in the system it did not detect any faults. They took it to the shop and checked it and came back and said my thermostat and belt and tensioner need to be replaced.

Well on the test sheet they gave me it said "Thermostat Shorted". Local mechanic said that thermostat is not electronic. is that true?

The car runs just fine and i have about 62,000 on it.

Any suggestions

thanks so much,

Maybe they mean its stuck open.

Oh..which means i need to change it right? Does it have to be done right away? Also, how can i check for bad belt? THANKS SOO MUCH

Originally Posted by seeth001

Oh..which means i need to change it right? Does it have to be done right away? Also, how can i check for bad belt? THANKS SOO MUCH

It HAS to be done right away. Your engine is magnesium and aluminum. If it overheats AT ALL in most cases you're looking at a new engine and they aren't cheap. Cooling system is pretty weak on modern cars; you don't want to chance anything going wrong.

It's not the serpentine belt - the water pump is electrically driven (from the alternator), not the belt.

Get it done asap - the thermostat is a $75-$100 part, but the labor is likely to be more than that.

The thermostat is electronic. When it shorts I believe it fails to wide open so that you don't overheat. It will cause long warm ups and excessive emissions. That is why you have the SES light on. It will need to be replaced. The thermostat runs about $100. An Indy would probably charge around $250 to install it. Belt and tensioner are recommended for replacement together about every 4 years. The probably last twice that long. I wouldn't worry about the tensioner until it starts making noise.

This is my understanding of how the OP's stat operates. It is made just like any other stat with the exception that it has a heating element in it to make it open faster.
The computer senses ambient temperature, engine temperature, and torque request (throttle position). It then decides if circumstances are such that more cooling will be needed. If so it heats up the stat with a 12V feed which causes the stat to open faster and wider than usual.
If the electrical portion fails, the stat can still open by operation of a wax pellet contained within a small expandable canister.
None of the sensing is done by the stat, it's a commanded only device.

Originally Posted by jburke4689

The thermostat is electronic. When it shorts I believe it fails to wide open so that you don't overheat. It will cause long warm ups and excessive emissions. That is why you have the SES light on.

Bingo - correct answer. Most people aren't aware of this, but the SES/CEL is always emissions related. The failure of the engine to reach optimum operating temperature adversely affects emissions.

Hi all.

I replaced the thermostat yesterday after the temp guage on the dashboard was at about 30%, running cold, Suggesting the thermo was stuck open, Also the heating inside the car wasnt great, further suggesting the same problem.

The temp guage went back to 50%, (12 o clock) which is normal and the heating returned to normal. Quite hot.

However, this only lasted for a while and now the problem of low heat inside the car and temp guage has returned to about 30%.

Does anyone have any experience of this oir any advice?

Note I only changed the main thermo.

Thanks in advance

Perhaps the waterpump is failing.?

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