M5 weirdest themostat ever? How does it even work? - Page 4

Beemer Guy · 29th December 2011, 14:06

I've replaced the t-stat on my ex-E38 and my fiance's ex-E46 and in both cases I just bought the entire housing and replaced it. A bit more expensive, yes, but much less prone to error. I suspect though that the ///M pricing may make this alternative less desirable.

It wasn't too bad on the E46 but a real PITA on the E38.

RICKROSS · 29th December 2011, 22:19

Quote:

Originally Posted by E39Sambo

I still have my old 540i as I'm doing a few jobs before selling it, one of which was to check out the thermostat. It turns out that on the 540/M62 engine the "coolant temperature" is a bit of a lie. Mine used to run at anything up to about 104 degrees before deciding it needed to cool things down. Apparently this is pretty normal, as the M62 motor doesn't report coolant temperature, so much as more of a "core engine temperature". The coolant is still around 80 degrees I believe.

Meanwhile, on my M5, I have an interesting issue. I suspected my thermostat was off as I have the "my temp gauge never goes above the 1/3 marker" issue, but I'm now suspecting my binnacle is at fault. My speedometer is lazy and always has been so I suspect that's been fiddled with and busted, but more worryingly every now and then my temp gauge goes zooming up to "fully mega hot" from its normal position while driving. The oil temperature then creeps up to around the centre marker. If I kill the ignition and immediately restart it, it all goes back to normal positions...

540i thermostat does run hotter but temp gauge also lies - gives a straight up 12 o'clock needle over a wide range of normal operating temps to 'relieve stress' for us sensitive types...

Whole housing replacement unecessary and much more expensive but an option I guess. I didn't even replace my o'rings as they looked fine and have held up perfectly with just a bit of non-setting silicone lube as insurance but you need some on hand for failures or if you pinch them on re-assembly. One of the best DIY's as you don't have to crawl under the car....

I'm sure I'm not alone in sharing concern about the soaring water and oil temps, get it sorted ASAP!

Cheers.

twastheglow · 29th December 2011, 23:07

So where should the temp gauge read when the car is at operating temperature? Mine reads about a needles width past the 1/3 marking.

jack eiler · 29th December 2011, 23:28

My answer- where ever you are happy. Mine always read about 1/3; I was happy, then this web site showed me the secret spot in the computer; KTMP, and I found out I needed a t-stat. I was then unhappy. ALL my previous BMW's were pretty much 12:00, and then my M5 has ALWAYS run about 1/3 up. When I bought the car it was running 12 o'clock the night I picked it up. Next day it started running about 1/3; and I thought it was normal. I have the parts in the trunk right now, they arrived yesterday, to do a stat. Best wish's.

Lord Lucan · 30th December 2011, 01:51

Oh well better go interrogate the OBC and see what the temp is telling me compared to the gauge and go from there as my temp needle sits about 1/3 of the way round the dial

technician117 · 30th December 2011, 04:47

The needle is suppose to be just left of center, or to be less exact - higher than the 1/3 mark, lower than the half way point. If you are questioning whether the car is running cold or not, disregard the gauge altogether and use the OBC secret menu to watch the temps. Anything below 78-79 at highway speeds is too low. What I have found, with my person experience, is that when the temp is only reading slightly low (77-78 all the time while driving) the thermostat is probably fine, but that inner seal that most people say you don't need to replace - needs to be replaced. The gasket part of that seal gets too hard and stays deformed in a position which allows extra coolant to flow past the thermostat body before you want it to... thus creating an over cooling situation.

Edit: Make sure you drive a good 10 minutes or more before you compare the OBC to the gauge. I have found that when the OBC first gets up to temp (79) the gauge will still be at the 1/3 mark. After a while longer the needle slowly moves up further, but the OBC temp will stay the same, or maybe hit 80.

jack eiler · 30th December 2011, 04:50

I was thinking about just replacing the stat; but, I will also replace the seal/gasket. Thanks-

twastheglow · 30th December 2011, 05:10

I can't seem to find the link on how to access the secret cluster menu. I'd like to check on my temperature. Can anyone walk me through it?

Maxiiimus · 30th December 2011, 05:30

Quote:

Originally Posted by twastheglow

I can't seem to find the link on how to access the secret cluster menu. I'd like to check on my temperature. Can anyone walk me through it?

Check out this link: Unlocking the High On Board Computer (OBC) - Bimmerforums - The Ultimate BMW Forum

jack eiler · 30th December 2011, 12:17

Or, under the FAQ section on this site. Instrumentation, secret menu. I leave mine unlocked.