Is this normal? Temp to drop when going real fast in cold weather

[LunatiC]

So I was doing 160km/hr (100mph) tonight -- it's 3:42AM local time here and it was about 8 deg C (46 deg F) ambient temp according to the OBC, when I noticed that the temperature gauge on my dash board was actually dropping.

Usually the needle is a hair-width's away from the middle notch, but tonight it dropped a fair bit to the left, past the notch between stone cold and middle.

I found this quite odd, does this make sense to anyone at all?

[Ross]

T stat ought to keep the temp up. Sounds like a lazy one, cheap replacement if in doubt.

[632 Regal]

ditto, replace it with a BMW stat available at your favorite online sources.
T stat ought to keep the temp up. Sounds like a lazy one, cheap replacement if in doubt.

[Blitzkrieg Bob]

T stats come in several temps 90, 88, etc.

and local shop tried to sell me a 72 for my M50tu...eeeh Wrong!

[TC535i]

Bad t-stat, my 540i ran just above blue the whole way back from Oregon. Swapped a fresh one in, and it sits at the middle all day.

[Tiger]

Yep... bad thermostat...

[LunatiC]

OK thanks for your replies guys. Looks like I'll be writing an email to Patrick from BMA ;)

[mattyb]

i would consider this normal. i do this quite often and the needle ussually drops just a fraction at higher speeds. makes sence to me.

[Alexlind123]

My thermostat used to be really sluggish, especially in cold weather, causing the engine to run cooler for long periods of time. I installed a new one and the engine heated up much more quickly. One other thing i noticed was that with the new thermostat, the final temperature is about a needles width right of center rather than exactly at center where is was before.

[LunatiC]

i would consider this normal. i do this quite often and the needle ussually drops just a fraction at higher speeds. makes sence to me.

OK well this has thrown a spanner in the works! (Haven't emailed Patrick yet). I noticed that my needle is fine now, it only did it at (really) high speed. It's not often that I drive so fast anyway.

If the replacement is cheap and easy to do, I might as well do it. How are you supposed to know what t-stat you need though, since there are so many? I had followed a little bit the "controversy" surrounding installing a different t-stat to what the factory put in your car and it does this and that for your engine which supposedly improves something, however I am not interested in this and just want to maybe replace the t-stat with the same spec as what was installed originally in the car.

[Blitzkrieg Bob]

THERMOSTAT 88CEL 1 11537511580 $37.94
THERMOSTAT 92 CEL 1 11537511083 $36.55

I'd go with the 92

I put in an 88, but the old on was a bmw 92 before in my M50tu.

Don't for get to include the O-ring and that funcky profile gastket for the water neck...oh yeah and if thats plastic, now's the time to replace that too.

[Paul in NZ]

i too would consider it normal,it makes sense,twice as much (cool) air flowing over the radiator for a medium increase in work.....thats how radiators work.If the air temp really dropped and the coolant temp dropped drastically the tstat would then kick in and begin to cycle.

[Dave M]

OK well this has thrown a spanner in the works! (Haven't emailed Patrick yet). I noticed that my needle is fine now, it only did it at (really) high speed. It's not often that I drive so fast anyway.


I wouldn't consider this normal. A small drop, maybe, but what you're experiencing, no way. I've driven in -40 at highway speed across Canada, with the temp pinned at 12:00. You definately have a lazy thermo. The only time you should see a decrease is if you're coasting (neutral) down a loooooong grade (mountains) where an idling engine cannot keep up with the cooling effect. I've seen this quite a few times, but we're talking 6-10 mile decents in neutral, fun :D

Dave

[Dave M]

i too would consider it normal,it makes sense,twice as much (cool) air flowing over the radiator for a medium increase in work.....thats how radiators work.If the air temp really dropped and the coolant temp dropped drastically the tstat would then kick in and begin to cycle.

Properly working thermo should not let it drop to the extent described (1/4 mark). Regardless of whether added speed or colder air is the cooling force, the thermos job remains the same: shut er' down....now. Lazy one will wait for a kick in the a$$ :D

[borderchris]

Hey there... I had the same issue; it would appear that your thermostat is partially dislodged. If it's hanging on by one leg, or even bouncing around in there (as mine was), it will vary between normal, when it's wedged in tight, and cold blooded when it breaks free again. Get in there and replace it- you are risking running rich and dumping fuel into your cats.

Chris