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E34 (1989 - 1995)

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  #1  
Old 09-03-2012, 07:50 PM
Hunter8511 Hunter8511 is offline
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Mein Auto: 1990 525i (E34)
Thermostat replacement Temp. question

Hey everyone. I'm flushing my cooling system and replacing some of the hoses for it. Since ill be down their, i want to change the thermostat for my piece of mind. I don't trust autozone for my parts so i was going to order it online. Problem is i don't know what temperature i should get for it. The high (80c), Medium(75c), or the low(71c). I would assume the lowest would be best for cooling but herd that could affect my engines performance. so i figured id ask the experts. Thanks guys.

1990 525i
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  #2  
Old 09-03-2012, 10:34 PM
paperplane94 paperplane94 is offline
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Mein Auto: 1989 525i M20B25
If it is a cooler opening temp your MPG will suffer.
You probably won't notice it drop though.
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  #3  
Old 09-03-2012, 10:45 PM
Hunter8511 Hunter8511 is offline
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Mein Auto: 1990 525i (E34)
So ill probably go with the mid grade temp then. Get the decent gas milage while making sure my temperature is more then ok.

How come cooler temps would make my gas milage suffer? I know very little about cars, so it perks my curiosity to learn as much as i can.
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  #4  
Old 09-04-2012, 10:46 AM
paperplane94 paperplane94 is offline
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When you first start the car it is cold. The engine computer knows this because the ECT sensor tells it so.
When the engine coolant is cold this translates to a cold engine. The engine computer compensates for this by injecting more fuel.
A colder thermostat will open sooner than the the rest and will therefore keep the engine coolant colder for a longer time from when you first start it in the morning. This will cause the Engine computer to inject more fuel due to the longer period of increased injection.


In short, colder coolant= colder engine -> more fuel injected-> less MPG's.
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  #5  
Old 09-04-2012, 10:49 AM
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goosefoot33 goosefoot33 is offline
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Your engine likes to run at a certain temperature, and the best gas mileage occurs at around that temperature (sorry I do not know the exact temp). The thermostats job is to keep the coolant at its optimal temperature, so the engine is also at its optimal temperature. Your thermostat is closed for several minutes after initial startup to allow the coolant (and engine) to get to the optimal temp as fast as possible. Once it's reached, the thermostat opens. Too low of a temperature will cause your engine to work harder and burn more fuel, resulting in decreased mpgs.
My explanations isn't the greatest, but I'm sure you get the idea. I think you're making a good call getting the middle-of-the-road thermostat. It might also be a good idea to order all of them, replace your old one with the like temperature new one, and then return the others. Alternately, you could partially disassemble your thermostat housing and see what you have now and just order that one. Like the saying goes, if it ain't broke, don't fix it!

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  #6  
Old 09-04-2012, 10:55 AM
paperplane94 paperplane94 is offline
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^Not all thermostats say what temp they are though...

Mine didn't.
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  #7  
Old 09-04-2012, 11:09 AM
Hunter8511 Hunter8511 is offline
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Mein Auto: 1990 525i (E34)
Thank you guys for all the responses. They help me understand it a lot better now. And not knowing the temp. Is why i wont buy this part from autozone. Im going to order it from a BMW website that has all the specifics labled. And from what i can tell its not broke. But not knowing its history. This little $20 fix could save me a lot of money in the future and helps my piece of mind. Thanks everyone again for the quick responses. I really appreciate it.
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  #8  
Old 09-04-2012, 02:06 PM
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goosefoot33 goosefoot33 is offline
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Quote:
Originally Posted by paperplane94 View Post
^Not all thermostats say what temp they are though...

Mine didn't.
Very true, if it's been replaced before it will most likely be stamped on the actual thermostat. If it's original from the factory it will most likely not be stamped.

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