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Discussion Starter · #1 · (Edited)
Hello everyone again
I got a 2000 E39 M5 with yet another faulty Thermostat.
I looked back at the my maintenance history and it seems that thermostats last me only one year. Is this normal $H!T that thermostats lasts only one year on S62?
 

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No, that's not normal. I had my car almost 5 years, only needed 3 new tstats.
 

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Id consider an aftermarket (non-Behr) thermostat from the likes of Stant or Gates. I put in a Stant and at 18+ months its going strong. If it fails anytime soon I will try a Gates, but I suspect it will be many years of trouble free service.

This thermostat is used in caterpillar diesels, and I can nearly guarantee the fleet operators of machine like that would not put up with a 1-2 year service life.
 

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Almost 4 years (December) and haven't put a new t-stat in yet. I know it is in the records that it had a new one shortly before I bought it and I have only put on around 17k in those 4 years.
 

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S62 newbie here. Bought my 2002 in November 2014 with 131K miles, now at 134K. Nothing in PO's records shows thermostat replacement, and I've not seen any reason to doubt normal operation; engine warms up normally and temp needle never goes past 12 o'clock, even in Texas heat. If it ain't broke why replace it?
 

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Because that is the M5 way..:grin
Haha. Seems to be sometimes.

I wouldn't condone replacing for no reason though. If you have to disassemble the housing for another repair, sure replace the $20 part, otherwise replace when it breaks (which is way to often based on reading here). The Behr seems to be short lived to say the least.
 

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Hello everyone again
I got a 2000 E39 M5 with yet another faulty Thermostat.
I looked back at the my maintenance history and it seems that thermostats last me only one year. Is this normal $H!T that thermostats lasts only one year on S62?
Why do you think it is faulty? Have you ever replaced the seal inside the housing? If you have the heater on then that can lower the temp if the car is under light load like a highway cruise.
 

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Why do you think it is faulty? Have you ever replaced the seal inside the housing? If you have the heater on then that can lower the temp if the car is under light load like a highway cruise.
Agreed. There HAS to be something else going on.

Malcolm
 

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Discussion Starter · #10 ·
Why do you think it is faulty? Have you ever replaced the seal inside the housing? If you have the heater on then that can lower the temp if the car is under light load like a highway cruise.
Interesting idea however about 2 years ago I had the same CEL code and it would not warm up properly and after just Thermostat replace it all worked fine for another 2 years. If it was a bad seal then replacing a Thermostat last time would not have been the solution. I do put good amount of driving every year (around 15k). I use heater for 2-3 month a year in December. Would be 2 years and around 30k miles count as average Thermostat lifespan?
 

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Not replacing the seal can cause premature failure of the new thermostat. That could be why we see these fail so often.

When I replaced mine the seal was very dry, brittle and sticky.

The thermostat body needs to be able to slide through the seal with as little friction as possible.
 

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I've replaced mine almost every year, with more recently being the exception. I'm going on about 2 years right now. The last time I replaced the thermostat I also did the inner ring. Now that we've had some cooler nights (60's F), while driving on the highway (no heat on) my gauge drops pretty far to the left compared to when it's a bit warmer, and the Test 7 readout keeps the temp at 78, but sometimes dipping more than that. I will likely do a thermostat this year and the ring again since I'll be in there. Of course I'll first keep an eye on it as the weather fully turns into Fall and see that it consistently runs cooler.
 

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Not replacing the seal can cause premature failure of the new thermostat. That could be why we see these fail so often.

When I replaced mine the seal was very dry, brittle and sticky.

The thermostat body needs to be able to slide through the seal with as little friction as possible.
Agreed. Look at a used t/s. You can see the rubbing marks on the side. The one time I replaced a t/s, I used a piece of wooden dowel to "massage" the lip of the seal so it sealed all round but the t/s slid up and down with minimal drag.

Malcolm
 

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Thermostat seal mod?

Agreed. Look at a used t/s. You can see the rubbing marks on the side. The one time I replaced a t/s, I used a piece of wooden dowel to "massage" the lip of the seal so it sealed all round but the t/s slid up and down with minimal drag.

Malcolm
Hi 68, was talking to another member this morn about low hwy temps dropping sub 79c while cruising down here, and its not exactly cold in Aus, only 2years on a new stat, and seal. His thought was to try just removing stat, rubbing down the seal lip a bit with sand paper so the stat moved easier, might be a good thing to try.
Is there any confirmation of this being a tried solution? Has it worked for you? OR just bite the bullet and replace stat every couple years?
Cheers
 

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There is one thing that we missed on this issue first time around. When I started traveling to the east coast and back I noticed it. If you are cruising at highway speed and light throttle, if the cab heater is on that will cool the engine enough for the temp to drop a bit below 78. 77 most of the time but I saw it hit 76 too. I could stop it by lowering the cabin temp with the AC off. We set the cabin temp and forget and you never know if the cab is being heated unless you turn the heat down completely.
 

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Just searching about this problem and glad to see I'm not alone (although it's little comfort). Replaced thermostat and seal ring 15 months ago at 85,000mi and it's running cold again. All through the summer it would stay at 78 at highway speed, higher around town. Now that temps are in the 50s, it will go down to 72, although a quick rev in neutral to 6000rpm will bring it to 75 instantly. Mileage is now around 91,000 and I can't believe it failed in 6k miles. Pathetic.

Edit: Just realized I have 94,000mi... so it lasted 9,000 miles.
 

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I never looked, as I had no reason to. Flushed the coolant every other year just as I have in any other car. The car was winter driven and operated in a range of perhaps -35 to plus 30 or so thru the 4 seasons with no issues getting to temperature in the winter and no overheating in the summer..Reading these various threads, I realize that I was very fortunate..
 
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