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Discussion Starter #1 (Edited)
Hi!

I just had my thermostat replaced, to my '99 Beast.

There was discussion about these temperatures of S62 engine just lately in some topic, but here's some fact to compare.


* The type of thermostat. Somebody said here that M5 thermostat is just like any other cars thermostat, nothing new under the sun. Actually, it's pretty unique type of thermostat, of course it can be same with other bmw models and I think it is, but as usual thermostat looks like this: http://www.innerauto.com/images/partImages/thermostat1.jpg

The M5 thermostat does not have any kind of flap like that, what closes and opens with the temperature.

It's actually an round housing like a "short piece of pipe", and it works by changing it's diameter through different temperatures. Water doesn't flow through it. Pretty wild as I have never seen thermostat like that. :eek:


And then the temperatures:


Before:

(Outside temperature around -5....0C)
After 1-2 mile of driving... Water ~55C / Oil ~40C
After 10miles of driving... Water ~65C / Oil ~60C
Once fully warmed... Water 68-72C / Oil ~same
Needle in the gauge was pointing just above the "circle" of the colder side

After:
(Outside temperature around -5....0C)
After 1-2 mile of driving... Water ~75C / Oil ~xxC
After 10miles of driving... Water ~80C / Oil ~76-80C
Once fully warmed... Water 80C / Oil ~85C
The gauge was pointing just above the "circle" of the colder side


I drove over 100km's today i.e., in city, highway, idling on the parking area... It was always 80C, no matter how you drive, needle pointing DIRECTLY to north all the time.


So, maybe this really is the way fully functional OEM thermostat should work? There is some cheaper ones in the market as well but roomer says that those are unable to keep the temperature up on 79-80C if weather is cold.

Maybe the carbon build-up problem is connected to bad thermostat somehow? Too cold temperature -> carbon build-up, and because car doesn't warm up to that 78C temperature where the DME thinks engine is fully warmed. (at least for me 72-75C temps gave trouble codes of too cold temperature?)

Maybe conrod bearing wear is seen in some cases because bad oil quality, and bad oil quality because oil temperature doesn't rise high enough to remove any water or gasoline from the engine oil?

Maybe too cold running temperatures causes the pretty low mpg's some have reported?

Just some silly thoughts, I'm not claiming these are true, just wanting to raise some thoughts for you guys. :dunno:

Anyways, this seems to be the way my car is supposed to work, and it's nice that it finally does it like it's supposed to. :cheers:
 

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Not true, coolant does flow through the thermostat. It actually opens in the middle, with the upper part separating from the flange.
 

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Not true, coolant does flow through the thermostat. It actually opens in the middle, with the upper part separating from the flange.
not really understanding your post. It (coolant) does flow thru the thermostat but there is no valve in the thermostat that opens and closes, as on a 'normal' thermostat.
I have one on my work bench, will take a pic tonight. There is no flap or hinge or anything that closes on the "correct" S62 (and S38, same unit) thermostat. As the OP said, the entire unit moves and works with the seal in the thermostat housing to open or close the flow of coolant either to the radiator or in the engine.

Also as with the OP, since replacing mine (and the seal), the coolant temp is never under 80C once the car warms up.
 

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Kind of hard to describe. When I say in the middle, I don't mean through it, I mean the upper section parts from the flange.

When the fluid is cold, the thermostat allows coolant to pass through the middle, into the upper portion of the housing. When it gets hot enough, the thermostat opens, and the whole upper portion moves and allows coolant to pass through into the lower portion of the housing. It doesn't change it's diameter or anything.

My coolant temp will dip down to 78C, but it may be because it's below freezing here, and the coolant cools off faster
 

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do m5s need these replaced often
I wouldn't say often, but it does seem to be a fairly common failure. My car has 60K miles on it, not sure what kind of mileage others have seen.
 

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had to replace my thermo at 56k miles. it was a $660k at the local stealer. Lots of labor because it sits begind the water pump i recall. It seems like a standard repair.
 

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not really understanding your post. It (coolant) does flow thru the thermostat but there is no valve in the thermostat that opens and closes, as on a 'normal' thermostat.
I have one on my work bench, will take a pic tonight. There is no flap or hinge or anything that closes on the "correct" S62 (and S38, same unit) thermostat. As the OP said, the entire unit moves and works with the seal in the thermostat housing to open or close the flow of coolant either to the radiator or in the engine.

Also as with the OP, since replacing mine (and the seal), the coolant temp is never under 80C once the car warms up.
I just replaced my own thermostat. There is a valve and is apparent when it's sitting in the thermostat housing. Outside of the housing, it looks like a disk with a spring.
 

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had to replace my thermo at 56k miles. it was a $660k at the local stealer. Lots of labor because it sits begind the water pump i recall. It seems like a standard repair.
$660,000???

Does not sit behind the water pump. It's right up top. You only have to lift the car because coolant change is necessary if you replace the thermostat.
 

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$660,000???

Does not sit behind the water pump. It's right up top. You only have to lift the car because coolant change is necessary if you replace the thermostat.
don't you hate that, "sir, we can replace your m5's thermostat, but we will require a lien on your house..."
 

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This is a hack job, but it's the best way to illustrate what happens with the thermostat when cold/hot



If you look at the inside of the top of the thermostat housing, you will notice two chambers, and the thermostat seal/ring/thing separates the two.

I'm not 100% sure if the thermost will completely block flow through the top, but my guess is it can once fully warmed.
 

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Mine failed at 130k miles, so yes, not bad.

It works when the substance in the core melts at or around 78C (the core is where the arrow in the above picture is by--small cylinder in middle). When it melts, it expands and compresses the thermostat, opening it up. This acts as a valve to allow coolant into the radiator to keep it cold. When it's cold, it bypasses the the radiator and pushes coolant down into the pump to be recirculated, allowing the engine to warm up quicker.

I noticed that when these fail in the BMW, it fails by leaving the thermostat open, using the radiator. This is much safer than the opposite.
 

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Thanks for posting this. Because of this post, I monitored the temp gauge today. The needle kept fluctuating between just right of the cold dot to just a tad to the left of the center but never right on center no matter how I drove. It never stayed in one place. Outside temp was mid 50s F. Then I switched on the AC and the temp appeared to permanently stay just a tiny bit to the left of the center...:dunno: Normal or time to replace the t-stat?

Car has 39,500 miles and it is an 03. Still under CPO warranty but how do I "convince" the dealer to replace the t-stat without a code?

Thanks,
Jim K.
 

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http://www.m5board.com/vbulletin/showthread.php?p=1246738#post1246738

Follow that to see what the actual temp is. once the car is warmed up, it should never fall below 79/80C

When mine was bad, it would only get to 68-70C, and if I turned on the heater full blast, it would drop 2-3 degrees rapidly. It's much more pronounced in cold weather
 
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Having tried to blame my low coolant temperature (75 degrees when cruising on the motorway) on low ambient temperatures, I finally bit the bullet and got BMW to replace the thermostat. It now sits at 80-81 degrees when cruising and about 85 degrees in town.

Too early to tell if this had a negative impact on MPG but I suspect so.

If you, like me, see the coolant gauge sitting around the first dot on the motorway, and it goes to the 12 o'clock position in city traffic I can only encourage you to go and have that thermostat replaced. Paid €300 for it, which wasn't as painful as expected.
 

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Having tried to blame my low coolant temperature (75 degrees when cruising on the motorway) on low ambient temperatures, I finally bit the bullet and got BMW to replace the thermostat. It now sits at 80-81 degrees when cruising and about 85 degrees in town.

Too early to tell if this had a negative impact on MPG but I suspect so.

If you, like me, see the coolant gauge sitting around the first dot on the motorway, and it goes to the 12 o'clock position in city traffic I can only encourage you to go and have that thermostat replaced. Paid €300 for it, which wasn't as painful as expected.
+1, this was exactly the same issue with my car too. 39K miles and thermostat was replaced under CPO warranty. Now it stays at center or maybe a tad to the left of center at like 11:45.
 

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I have just over 38,000 miles, and my thermostat is on the way out. Should I be ordering one and having it installed, or just go to a good independent and have them to the whole thing, just looking to save a few dollars if I can. My Thermostat sits to far left and only comes to the middle around idle or just running through side streets. I have a few good independent shops to call and quote in the Chicago land area.
 

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you think this thermostat is bad to do, try a 2001 Audi A6 with the 2.8L, shoot even the VW Passat with the 2.8l. talk about major overhaul of the front of the car! bumper, radiator, headlights, timing cover, timing belt, accessories, etc...(thats just the big stuff!) almost 6hrs in work. eee!
had one in my moms car go bad and the car wouldn't stop getting hot. it stayed stuck closed. THAT was a job.
 
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