Re: Larry Abelkop <bafox@domain.elided>

[Jim Cash <j.cash@xxxxxxxxxxxx>]

Larry writes:

> I have just purchased a 97 540i with the computer controlled thermostat
> & I am trying to decide if it is functioning correctly. When its cold
> outside, the temp gauge goes up very quickly to just above the blue
> range & stays there about 5 minuites before it moves up to the first
> white line where its stays another 5 minutes before going to 1/2 scale.
> Even after 10 minutes on the highway it will go back down almost to the
> first white line and then back to 1/2 scale.
> Any comments from other owners with this electronic thermostat.?


Larry - I am no expert on that system but I will share what I know.


The computer controlled thermostat is designed to keep the engine
temperature more closely within the best operating temperature range - I
think it strives to keep it at about 110C.

The temperature guage is driven by a coolant temperature sensor, but it
is a different sensor than the one that the engine "computer" uses to
keep track of the engine temperature. 


I know that the temperature guage in my instrument cluster does not
exactly follow the real engine temperature. I have not seen the "drops"
in the guage movement that you have, but mine moves slowly and steadly
up to the midway mark (straight up) and then seems to stay there with
very little variation. It may have similar pauses to what you describe -
I have not noticed any prolonged pauses

But I have noticed that the guage gets to that midway point while the
engine temperature is still below 80C, and it does not move any farther,
even while the actual temperature continues to climb up to its proper
range of 108 - 111 C.

So my guage says the engine has come to operating temperature, long
before it has reached it's peak operating temperature. 


In your case, because of the drop, you may have a faulty guage sensor,
or maybe the guage itself. Your dealer can run a diagnostic to see if
the sensor for the engine computer is functioning properly, and whether
the computer is controlling the temperature properly. They can monotor
the guage as they monotor the actual increase in temperature - if it
does not follow the rise in actual temperature then there is a problem.

On the other hand it may be the way you are warming it up.  Mine is an
automatic, and the computer holds the car in the lower gears for a
longer time during the first few minutes of running to help it warm up
quickly. Since yours is a manual (540i) it will not warm up as quickly
unless you are also running it a little longer in the lower gears
(delaying your shifts). 



Hope that helps

Cheers

Jim Cash
London, Ontario, Canada
BMW CCA 102929
E39  97 540iA

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