New Thermostat, Now Running Hot

[dk2020]

I recently installed a new thermostat, and now the temp does not drop back down on the freeway?

Let me give a little quick history…. Basically, my heat worked, until I stopped, or in stop and go traffic, it would start blowing cold air until I started moving again. So I checked everything logical, fluid levels and such, and figured it was the thermostat. So I drained, replaced the thermostat, flushed and refilled, and also replaced the hose on the back of the engine that is shrink-wrapped to the Engine Breather hose. It filled slowly and awkwardly, bubbled over a lot before it took the coolant, but I have checked the levels every day since and it is full.

Now when it heats up to ½ in stop and go, then I hop on the freeway it stays at ½ instead of dropping to ¼ like it should.

One side note, my MPG is up by almost 1.5 to a solid 31 @ 41mph ave. speed.

Any Ideas what might not be clicking? Anybody know what sensor tells it your on the freeway and not in regular traffic?
Basically, I would just hate to replace the thermostat again, $60 from the stealer, and all that antifreeze.... also, a bit of a mess.

Thanks,

[J!m]

The temp gage should be at 1/2 all the time- regardless of outside temp., road, speed a/c on or off etc. It dropping to 1/4 (if already above 1/4) was a sign of problems.

It was dropping lower before (and you had no heat) due to air in the system. At idle, the temp sensor was getting no coolant, and read inproperly. Then as rpm's increase, it cavitates, and causes water slosh, so the gage is reading water temp., not air temp. (basically, an un-primed pump)

Common problem with these since the coolant system is difficult to bleed completely.

You are fine now, it sounds like. Gage at 1/2 (straight up) is perfect.

Better mileage is due to proper operating temperature as well.

[bimmerboi318]

yes it should stay at 1/2 once warmed up. mine will not warm up unless the outside temp is about 75 F. does this mean i have air in the system? usually it stays at about 1/4-1/3 until the outside temp gets pretty warm.

[J!m]

Yes, it seems like there is still air if the temp won't come up to 1/2 just sitting at idle.

I't is quite difficult to get all the air out. My Defender's Tdi is also a pain in the butt..

It could be a bad sender, but not likely- they seem to last for ever (I've never replaced one on a BMW...

[bimmerboi318]

maybe my situation is unique. at idle it will warm up to temperature. however once i get moving and it's under 60-70 degrees or so, the temp will drop. i thought that maybe the thermostat was stuck open. i havent replaced it yet.

[hotdog19d]

mine has the same problem stays cool unless I sit and idle, I bled the system and didn't help any, oh well I would rather have it run a little cool than a little hot :D

[J!m]

Does the cooling fan run al the time? If so, this could be the problem. If the fan is running while you are driving (and the a/c is not on) this may over-cool on a 60-70 deg day. Too cool is better than too warm yes, however the fuel economy will be slightly worse. I don't forsee any permanent damage, unless there IS air in the system. This will cause 'hot-spots' which could cause other components (such as head gaskets) to fail...

If the fan does run constantly, perhaps a faulty temp switch?

[hotdog19d]

no my fan only runs after it's sat and idled a while

[dk2020]

J!M,
Thanks a million for the info, since I was about to scream at the dealer for giving me a bum thermostat. I have had my TI for 3+ yrs and it had always run that way, and was stirctly dealer serviced prior to me getting it, so I thought it was suposed to run that way. Guess at the last coolent flush, prior to me getting it, the stealer did not do thier job filling the coolent.
FYI: filling the coolant is a pain! Took me and my mechanic 20+ minutes to get all the air out, and even then we were not sure it was all out, but I have checked it often and it is good to go.

ps, just did a 1200+ mile trip since my post, got 32mpg this time, all highway of course. Man these cars run like a top! Up to 120,000 miles now! Just getting broken in about now I guess.... :D

Thanks again!