E36 Engine Temperature

I hoping someone here might know what the problem is and how to fix
it.

On a 1995 BMW 318i 5-speed, the engine coolant temperature appears to
be operating perfectly with the needle in the mid way point. Never has
overheated, and I just replaced the original thermostat last year due
to not warming up during the cold winter months here in Southern
Ontario (Canada).

The problem is highway driving during the colder months at speeds
above 100km/h (above 60mph) and usually in 5th gear, the coolant gauge
will drop to almost the bottom of the cold (blue) region of the gauge,
and there is a slight drop in heat temp comming from the heater in the
interior ... if I slow down or shift into 4th, the gauge will start to
rise back up.

The thermostat was just replace 8 months ago, and from what I know,
seems to be still fine ... the coolant level is fine and there are no
leaks, the coolant mix is fine from what BMW had recommended, the
engine belts are good ...

It has me concerned, as the cooler running temperature on the highway
may affect engine life.

Anyone else seen this before?

Any thoughts or suggestions?

THanks,

On Tue, 14 Dec 2004 14:57:11 -0800, Jonathan wrote:

> I hoping someone here might know what the problem is and how to fix it.
>
> On a 1995 BMW 318i 5-speed, the engine coolant temperature appears to be
> operating perfectly with the needle in the mid way point. Never has
> overheated, and I just replaced the original thermostat last year due to
> not warming up during the cold winter months here in Southern Ontario
> (Canada).
>
> The problem is highway driving during the colder months at speeds above
> 100km/h (above 60mph) and usually in 5th gear, the coolant gauge will drop
> to almost the bottom of the cold (blue) region of the gauge, and there is
> a slight drop in heat temp comming from the heater in the interior ... if
> I slow down or shift into 4th, the gauge will start to rise back up.
>
> The thermostat was just replace 8 months ago, and from what I know, seems
> to be still fine ... the coolant level is fine and there are no leaks, the
> coolant mix is fine from what BMW had recommended, the engine belts are
> good ...
>
> It has me concerned, as the cooler running temperature on the highway may
> affect engine life.
>
> Anyone else seen this before?
>
Yep, when the stat is bad and sticks open. It is easy enough to check.
Pull the stat, stick it in a pot of water, heat on a stove and measure the
temp the stat opens at. Then turn off the heat and see at what temp the
stat closes.

Or, just get a new stat and put that one in. The odds of two OEM stats
being bad is pretty low.


--
The instructions said to use Windows 98 or better, so I installed RedHat.

> Anyone else seen this before?

Yes, sort of. But this is for an E30/M20. It may still be true for you
though ...

I suspect this is due to the viscous coupling. It's actually operating
correctly, but not very helpfully!

The VC 'lets go' at around 2500 rpm. So driving in 5th at rpm below this
means that the cooling fan is engaged, and probably overcooling the engine.

When you drop into a lower gear and the rpm rise, the VC drops out, so the
cooling is less and the engine runs warmer.

My 320i suffers from this in reverse. At 70mph in 5th (2600 rpm) the VC
drops out, but there is not enough air flow through the rad, so the temp
rises. Slowing down engages the VC and the temperature drops. Speeding up
increases the air flow through the rad and the also temperature drops!

In 5 years of ownership the car has never overheated, so I don't worry. I
have had a couple of stats fail though (usually stuck open) so you might as
well replace yours. They're cheap, but bleeding the air out of the system
can be tricky.

Al.

The airflow from driving at this speed is much greater than the VC fan
produces.
It sounds like a faulty stat but could also be an air lock or sender fault.
does the interior heater go cold when the temp drops?
Jim.

"Al" > wrote in message
. 4...
> > Anyone else seen this before?
>
> Yes, sort of. But this is for an E30/M20. It may still be true for you
> though ...
>
> I suspect this is due to the viscous coupling. It's actually operating
> correctly, but not very helpfully!
>
> The VC 'lets go' at around 2500 rpm. So driving in 5th at rpm below this
> means that the cooling fan is engaged, and probably overcooling the
engine.

> When you drop into a lower gear and the rpm rise, the VC drops out, so the
> cooling is less and the engine runs warmer.
>
> My 320i suffers from this in reverse. At 70mph in 5th (2600 rpm) the VC
> drops out, but there is not enough air flow through the rad, so the temp
> rises. Slowing down engages the VC and the temperature drops. Speeding up
> increases the air flow through the rad and the also temperature drops!
>
> In 5 years of ownership the car has never overheated, so I don't worry. I
> have had a couple of stats fail though (usually stuck open) so you might
as
> well replace yours. They're cheap, but bleeding the air out of the system
> can be tricky.
>
> Al.

Jonathan wrote:
> I hoping someone here might know what the problem is and how to fix
> it.
>
> On a 1995 BMW 318i 5-speed, the engine coolant temperature appears to
> be operating perfectly with the needle in the mid way point. Never has
> overheated, and I just replaced the original thermostat last year due
> to not warming up during the cold winter months here in Southern
> Ontario (Canada).
>
> The problem is highway driving during the colder months at speeds
> above 100km/h (above 60mph) and usually in 5th gear, the coolant gauge
> will drop to almost the bottom of the cold (blue) region of the gauge,
> and there is a slight drop in heat temp comming from the heater in the
> interior ... if I slow down or shift into 4th, the gauge will start to
> rise back up.
>
> The thermostat was just replace 8 months ago, and from what I know,
> seems to be still fine ... the coolant level is fine and there are no
> leaks, the coolant mix is fine from what BMW had recommended, the
> engine belts are good ...
>
> It has me concerned, as the cooler running temperature on the highway
> may affect engine life.
>
> Anyone else seen this before?
>
> Any thoughts or suggestions?

What you are describing is that the ngine will warm up when idling (with
the limited airflow through the radiator that the VC fan creates) but
goes below optimum temperature with the increased air-flow of driving
faster.

What is happening is the coolant in the radiator is at a lower
temperature when driving faster. This is 100% normal occurance in cold
weather. What should happen is the thermostat should regulate the
engine temperature regardless of the radiator temperature.

Your problem is definitely the thermostat. There is nothing else that
will cause the engine temp to go too low (especially after it has
already reached temperature). Your thermostat is not closing fully.
You said that you had replaced it 8 months ago for another problem, what
did you replace it with?

Try replacing it again with a different OEM brand or an OE BMW one.

-Fred W

Fred W wrote:
> Jonathan wrote:
> > I hoping someone here might know what the problem is and how to fix
> > it.
> >
> > On a 1995 BMW 318i 5-speed, the engine coolant temperature appears
to
> > be operating perfectly with the needle in the mid way point. Never
has
> > overheated, and I just replaced the original thermostat last year
due
> > to not warming up during the cold winter months here in Southern
> > Ontario (Canada).
> >
> > The problem is highway driving during the colder months at speeds
> > above 100km/h (above 60mph) and usually in 5th gear, the coolant
gauge
> > will drop to almost the bottom of the cold (blue) region of the
gauge,
> > and there is a slight drop in heat temp comming from the heater in
the
> > interior ... if I slow down or shift into 4th, the gauge will start
to
> > rise back up.
> >
> > The thermostat was just replace 8 months ago, and from what I know,
> > seems to be still fine ... the coolant level is fine and there are
no
> > leaks, the coolant mix is fine from what BMW had recommended, the
> > engine belts are good ...
> >
> > It has me concerned, as the cooler running temperature on the
highway
> > may affect engine life.
> >
> > Anyone else seen this before?
> >
> > Any thoughts or suggestions?
>
> What you are describing is that the ngine will warm up when idling
(with
> the limited airflow through the radiator that the VC fan creates) but

> goes below optimum temperature with the increased air-flow of driving

> faster.
>
> What is happening is the coolant in the radiator is at a lower
> temperature when driving faster. This is 100% normal occurance in
cold
> weather. What should happen is the thermostat should regulate the
> engine temperature regardless of the radiator temperature.
>
> Your problem is definitely the thermostat. There is nothing else
that
> will cause the engine temp to go too low (especially after it has
> already reached temperature). Your thermostat is not closing fully.
> You said that you had replaced it 8 months ago for another problem,
what
> did you replace it with?
>
> Try replacing it again with a different OEM brand or an OE BMW one.
>
> -Fred W

> > Your problem is definitely the thermostat. There is nothing else
> that
> > will cause the engine temp to go too low (especially after it has
> > already reached temperature).

an air lock at the temp sender gives these exact symptoms, at low speeds/
air flow the sender will show the correct temp due to convection, when the
air flow increases the cooling effect is greater than the heating effect
from convection so the indicated temp drops.

I've worked on a lot of cars over the years, and this definitely has me
stumped !!!

After reading some of these other posts, I changed thermostat (which
was only 8 months old) thinking that maybe it was just defective and
failing slowly, as when the gauge temp dropped, so did the cabin heater
temperature.

Installed the brand new 92 deg C thermostat, carefully filled and
worked the air out, checked coolant 50/50 mix which was good to -37C
(-34.6 F) as recommended by BMW ....

Took the car out for a drive and the coolant gauge rises up to middled
gauge range, but STILL drops off in 4th or 5th gear, or when the engine
isn't under high loads ... the ambient temperature today was 0 C (32 F)
.... which makes me think that the NEW thermostat isn't staying closed
to regulate engine temperature, or something else is amiss?

My logic tells me:
1) The odds of 2 new thermostats being bad from the dealer is unlikely
(purchased 8 months apart)
2) Can't be the coolant mix, it's a 50/50 mix using BMW coolant and
tested with a hydrometer (-37 C)
3) Failed water pump would cause overheating problem ...

Can a failed/defect viscous fan clutch create the same effect as a
faulty thermostat?

The fan free wheels pretty easy when cold, but hasn't been tested hot
yet ...

On Sat, 01 Jan 2005 15:51:48 -0800, nikonbuff wrote:

> I've worked on a lot of cars over the years, and this definitely has me
> stumped !!!
>
> After reading some of these other posts, I changed thermostat (which was
> only 8 months old) thinking that maybe it was just defective and failing
> slowly, as when the gauge temp dropped, so did the cabin heater
> temperature.
>
> Installed the brand new 92 deg C thermostat, carefully filled and worked
> the air out, checked coolant 50/50 mix which was good to -37C (-34.6 F) as
> recommended by BMW ....
>
Anytime a thermostat is supected, but not definitely known to be bad, it's
a good idea to test the old stat before swapping it out. That's simply a
matter of placing the stat in a pot of water and slowly heating it.
Monitor the temperature of the water and note when the stat opens. If it
is opening too soon or too late you'll sone know. The turn off the heat
and slowly add cool water and note where it closes.

While it seldom happens, you can wind up replacing a bad stat with one
that's bad out of the box. The simple test above will determine if that's
the case.

> Took the car out for a drive and the coolant gauge rises up to middled
> gauge range, but STILL drops off in 4th or 5th gear, or when the engine
> isn't under high loads ... the ambient temperature today was 0 C (32 F)
> ... which makes me think that the NEW thermostat isn't staying closed to
> regulate engine temperature, or something else is amiss?
>
> My logic tells me:
> 1) The odds of 2 new thermostats being bad from the dealer is unlikely
> (purchased 8 months apart)

It can happen...

> 2) Can't be the coolant mix, it's a 50/50 mix using BMW coolant and
> tested with a hydrometer (-37 C)

Coolant mix wouldn't have anything to do with this...

> 3) Failed water pump would cause overheating problem ...
>
Yep...

> Can a failed/defect viscous fan clutch create the same effect as a
> faulty thermostat?
>
> The fan free wheels pretty easy when cold, but hasn't been tested hot
> yet
>
The fan or the stat are the only things that might cause an under cooling
situation with very low outside temps. The fan can tested by seeing if you
can stall it out with a rolled up newspaper with the engine idling. Be
gentle on those plastic fan blades.

Well there is one other thing that might have bearing on this. Once, when
I had the belly pan off of a 735 and drove it that way at highway speeds
in sub-zero temps the engine ran a bit cold. I figure that too much cold
air was circulating through the engine compartment and the problem went
away when I put the pan back on.

--
The instructions said to use Windows 98 or better, so I installed RedHat.

wrote:

> I've worked on a lot of cars over the years, and this definitely has me
> stumped !!!
>
> After reading some of these other posts, I changed thermostat (which
> was only 8 months old) thinking that maybe it was just defective and
> failing slowly, as when the gauge temp dropped, so did the cabin heater
> temperature.
>
> Installed the brand new 92 deg C thermostat, carefully filled and
> worked the air out, checked coolant 50/50 mix which was good to -37C
> (-34.6 F) as recommended by BMW ....
>
> Took the car out for a drive and the coolant gauge rises up to middled
> gauge range, but STILL drops off in 4th or 5th gear, or when the engine
> isn't under high loads ... the ambient temperature today was 0 C (32 F)
> ... which makes me think that the NEW thermostat isn't staying closed
> to regulate engine temperature, or something else is amiss?
>
> My logic tells me:
> 1) The odds of 2 new thermostats being bad from the dealer is unlikely
> (purchased 8 months apart)
> 2) Can't be the coolant mix, it's a 50/50 mix using BMW coolant and
> tested with a hydrometer (-37 C)
> 3) Failed water pump would cause overheating problem ...
>
> Can a failed/defect viscous fan clutch create the same effect as a
> faulty thermostat?
>
> The fan free wheels pretty easy when cold, but hasn't been tested hot
> yet ...

You should definitely be able to hear fan noise at speed in 4th or 5th gear
if it has seized. Running at that ambient temp there should be no engine
noise other than a soft purr. I hear my fan cut in on "hot" days all the
time at road speed on the freeway. (When it's 90-100 deg or so)

Any chance there is something amiss in the thermostat housing/gasket setup
that would let extra coolant circulate even if the thermostat stays closed?

Seems like you're on the right track - only thing that should do this is
extra coolant flow - only other possibility might be a failed temp sensor,
but it would seem that the temp sensor would have no idea about what speed
you were running or what gear you were in.

Do let us know what you find.

Frank