Can over cooling be caused by air?

[doogie]

I know most mentions of lack of correct bleeding revolve around over-heating.... I have over cooling - my temp gauge never reads 12, always the tick before that, so I read through the advice here and assumed a bad stat (I've already replaced it but with a cheap one) so I just bought a new stat from the dealer and installed it and still same problem. One thing though, my thermostat cover's bleed screw is jammed in tight and the nut is worn away.... I tried with WD40 and pliers and various things and I just could not get it loose, so I can't bleed from the stat housing - is an air bubble there likely to be causing my problem? I'm going to call the dealer today and see if they've got a new cover in stock (I ordered in and got a new bleed screw but I cannot get the old one out at all).... do you think that will solve it or am I barking up the wrong tree completely?

Thanks

Doogie

[philbyil]

Don't drive yourself nuts....a tick before 12 (11 oclock) is just fine!
Mine was always this way (for 7 years!) until I changed my water pump and thermo...it now shows 12.00. Didn't worry about that either

[Kalevera]

Yeah...that's completely normal...

[liquidtiger720]

mine is a whole needle width over 12. =)

[Hector]

to get the most from the engine. The engine control management system is designed to work with a thermostat set to a specific temperature whether it's 88 C or 82 C (or 81 C I think). A temperature that is constantly lower than this may not allow the computer to control the engine properly for operation at peak performance. Maybe others here on the board may have additional insight.

Here's an excerpt on a similar topic
http://www.northstarbmw.org/index.aspx?ns=TechArticles

"Thermostats maintain the correct temperature for both the passengers and the motor. If your thermostat is allowing your engine to run cooler than recommended the engine computer may never allow the fuel injection to work properly, causing poor fuel mileage, high emissions, poor performance and possibly fuel dilution in the motor oil. Typically, you would see this as a drop in engine temperature in cold weather, especially in highway driving. In the last few years BMW is using a computer controlled thermostat to allow for tighter control of engine temperature. This is done by building a "normal" thermostat that runs at a very high temperature. Incorporated in the design is a very small electric heating element that is controlled by the engine computer. By using the coolant temperature sensor as a feedback signal the engine computer can regulate the engine temperature by supplying current to this heating element as needed to cool the motor. Unfortunately BMW missed the mark in an early design of these thermostats on the six cylinder motors. An unacceptable level of failed thermostats has led to many cars being recalled to have the thermostat replaced with the newest design. Owners of affected vehicles will receive a notice in the mail from BMW."

[ryan roopnarine]

normal. in fact, if i were to go drop some watter wetter in my antifreeze right now, i could consistently get it to stay at 1 notch below for the next 5k miles. right now, it sits at 12, and may go down to 1 below if its colder than 40 degrees F outside, or if i've been letting it loaf on the highway for an hour or two.

I know most mentions of lack of correct bleeding revolve around over-heating.... I have over cooling - my temp gauge never reads 12, always the tick before that, so I read through the advice here and assumed a bad stat (I've already replaced it but with a cheap one) so I just bought a new stat from the dealer and installed it and still same problem. One thing though, my thermostat cover's bleed screw is jammed in tight and the nut is worn away.... I tried with WD40 and pliers and various things and I just could not get it loose, so I can't bleed from the stat housing - is an air bubble there likely to be causing my problem? I'm going to call the dealer today and see if they've got a new cover in stock (I ordered in and got a new bleed screw but I cannot get the old one out at all).... do you think that will solve it or am I barking up the wrong tree completely?

Thanks

Doogie

[doogie]

I've explained myself badly; by a tick I meant the next white line, 1/4 of the way up the scale.

Could that be caused by air in the system? I've ordered a new stat cover which will be in tomorrow so I will be able to bleed there tomorrow.

[Kalevera]

Oh...that happened to me a few weeks ago when I replaced my tstat...The problem turned out to be that I'd installed the new TSTAT rubber o ring incorrectly (wrong side). With the old tstat, it worked fine...the new one would creep to 3/4.

There's a huge thread on this I wrote a few weeks back..."cooling system problems "

Here's what I did (in short):

- Drained the rad
- Pulled the tstat housing
- Reseated the tstat, put it all back together.

Since you have an M20, it may be different...I bet your exp tank is integral to the radiator. But you've got to be able to bleed the sucker. (also not sure if this applies to m20's): drill a 1/16" bleed hole due north on the tstat. Made my bleeding process effortless.

Best, whit

[Dash01]

Rather than replacing the cover, you could remove it use penetrating oil from the bottom side of the screw. If that does not work, consider re-tapping the hole for a slightly larger bleed screw.

Back to the over-cooling issues: Once you have the bleed screw made usable, do the bleeding thing and check temp. If still running cool, check the temp sender. Could be, the temp sender is sending erroneous input to the gauge, or the gauge is off a bit, rather than an overcooling situation, per se.

[doogie]

I've replaced the temp sender already, and when I short it the gauge goes to 100%.... I do think it is over cooling a bit because as far as I can tell it smells too rich... but I have thought the gauge could be a bit iffy. I'll have a look in Bentleys to check resistances of the sensors at various temps.