[Drivaar]

So... my thermostat failed (got "Service Engine Soon" light), so I took it to a shop for repair.

After I got the car back, engine oil temp is up to 230 F to 240 F... it used to be almost always 220 F.

Apparently the difference is because they put in a plastic thermostat to replace the aluminum one that they removed. They're saying the plastic was OEM, but the aluminum one they removed came with the car, so obviously that is OEM too.

I always figure that running a lower temp consistently will be better for the engine -- after adding the oil cooler, temps have been solidly 220 F (unless pushing very hard), whereas before the oil cooler the temps were like 240F consistently.

So, the question is: plastic vs. aluminum thermostats... which is really OEM for a 2007 335i built without an oil cooler (but with an oil cooler added later), and does it matter?

Any advice would be great!

Thanks!

[Drivaar]

(bump)

[Drivaar]

(bump again)

Sorry to bump again... I think this is sort of a rare topic, but I'm hoping some expert here can help... Thanks!

[DMafia46]

what are you asking?

[Drivaar]

I added the question in bold... it was the thread title so I figured it would be clear, but I see how it might not have been. Thanks DMafia46!

[mike3000fl]

your assumption lower temp is better is not necessarily true.

different conditions have different optimal temps. fuel economy vs performance...etc.

the e90 is part electronic. this allows the car to control it kind of.

your old thermostat failed and was stuck open. thats how they fail in an e90. open thermostat equals lower temps.

now the thing can close, temps are higher.

if the temp was too high, the car would have the water pump work harder to cool it.

don't worry, the car has a computer that is controlling the speed of the water pump and to a certain extent the thermostat. let it do its thing.

the temps while broken were bad, your temps now are what the car wants the temps to be.

plastic versus metal = no big deal. many people have done the change and have plastic.

[DUI Elite]

Plastic water pumps can have a better fighting chance against coolant that has broken down (over time) compared to aluminum setups. With proper maintenance of coolant, i believe their differences are negligible. Not sure but i'd assume same principle applies to he thermostat.

My 09 Audi Q5 came with an aluminum impellor blade but the housing cracked very prematurely (15k miles on it) and Audi gave me a new pump (with a plastic impellor) that they "redesigned."

i think many companies redesign to use plastic for durability. E36's had the same redesign with their water pumps.

[spool twice]

I see many more advantages of having plastic parts in the cooling system than metal parts. Many will disagree with me, but they are entitled to their own opinions, even if it's wrong

[ChasVS]

The housing in plastic which has no affect on Thermostat performance.

[Drivaar]

Awesome, thank you all for the informative responses!

One last question: I found it interesting that the old engine temp was stuck at 220F for months even before the check engine light came on...

Sounds like the thermostat was stuck open the whole time, but it took a while for the fault warning to come up?

Either way, what you all are saying makes sense. Thank you!

[mike3000fl]

yup, now go drive it...

[AddictedToBavarian]

Originally Posted by mike3000fl

your assumption lower temp is better is not necessarily true.

different conditions have different optimal temps. fuel economy vs performance...etc.

the e90 is part electronic. this allows the car to control it kind of.

your old thermostat failed and was stuck open. thats how they fail in an e90. open thermostat equals lower temps.

now the thing can close, temps are higher.

if the temp was too high, the car would have the water pump work harder to cool it.

don't worry, the car has a computer that is controlling the speed of the water pump and to a certain extent the thermostat. let it do its thing.

the temps while broken were bad, your temps now are what the car wants the temps to be.

plastic versus metal = no big deal. many people have done the change and have plastic.

Lol this guy always has awesome answers.