in juxtaposition to the 'no heat' thread below...

[slater]

in contrast to the other thread: when idling, the car warms up fine and the temp gauge gets to 12 o'clock and all is well; heat flows from the vents.

when underway, the temp gauge drops to 10 o'clockish and i don't get any heat (or really anything at all) from the vents; returning to idle and waiting sees the temp gauge rise back to 12 o'clock and heat resumes from the vents.

doesn't seem like a t-stat or water pump issue, because the car does indeed produce heat and get up to temp when idling.

coolant temp sensor?

thanks all!

peter

[brettbimmer]

I assume that you have checked to be sure that your coolant is up to the proper level? Just thinking about a possible air block on the system causing you trouble.

EDIT: Any idea if/when the thermostat/water pump/expansion tank have been replaced?

EDIT 2: Coolant temp. sensor sounds suspect to me given the symptoms noted, as the thermostat is obviously opening up once the car is up to temperature, causing the temp. gauge to drop back to the 10 o'clock position.

[Pip]

How many miles on the car? Temp sensor seems like a fix that would work and the oring goes out around 60k-80k miles so would be beneficial to change anyways if the sensor is suspect.

[kayger12]

Thermostat stuck open.

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[Pip]

Thermostat stuck open.

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He could easily check by driving from the start and seeing how long it takes/if it ever gets to operating temps. Also it would be useful for the OP to use the trick to see temp displayed on the dash when doing this.

[slater]

He could easily check by driving from the start and seeing how long it takes/if it ever gets to operating temps. Also it would be useful for the OP to use the trick to see temp displayed on the dash when doing this.

if i drive right off, the needle never gets up to temp. i found the hidden code reference on the site, but the directions don't seem to work for me (hold down the trip reset button while turning the car on - i don't get the menu prompt).

peter

[slater]

How many miles on the car? Temp sensor seems like a fix that would work and the oring goes out around 60k-80k miles so would be beneficial to change anyways if the sensor is suspect.

228K miles. :)

the PO was not a technical guy - he brought it into the dealer or his BMW-specific indie for everything. i looked through the records i have and noted one coolant hose replacement about 2 years ago - however, there are some missing records and the PO is sending them to me.

peter

[slater]

I assume that you have checked to be sure that your coolant is up to the proper level? Just thinking about a possible air block on the system causing you trouble.

EDIT: Any idea if/when the thermostat/water pump/expansion tank have been replaced?

EDIT 2: Coolant temp. sensor sounds suspect to me given the symptoms noted, as the thermostat is obviously opening up once the car is up to temperature, causing the temp. gauge to drop back to the 10 o'clock position.

i think it may very well be a good idea at this point to go ahead and replace the water pump, t-stat, coolant expansion tank, coolant temp sensor(s) and heater valve all at once.

peter

[Pip]

if i drive right off, the needle never gets up to temp. i found the hidden code reference on the site, but the directions don't seem to work for me (hold down the trip reset button while turning the car on - i don't get the menu prompt).

peter

I think you've answered it. If the car doesn't get up to temp when driving right after startup it is because the Tstat is stuck open as Keith mentioned. But a preventative cooling system refresh isn't a bad idea if the funds are there.

[slater]

I think you've answered it. If the car doesn't get up to temp when driving right after startup it is because the Tstat is stuck open as Keith mentioned. But a preventative cooling system refresh isn't a bad idea if the funds are there.

thanks, sean. funds are never plentiful, but i'm very much a 'while i am in there' kinda guy. will likely do the water pump, belts, temp sensors while i'm doing the t-stat.

peter

[ELCID86]

Expansion tank...

[brettbimmer]

Thermostat stuck open.

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That is what I was originally thinking (note my edits to my post), but seems odd that it would read normal temp. and supply heat with the thermostat stuck open. If it was stuck open, wouldn't the car never get to proper temp. even at idle as the thermostat is already open?

+2 for the cooling system overhaul if you don't know if/when it was done! No need to be stranded on the side of the road, or overheat the engine due to a cooling system failure.

[kayger12]

That is what I was originally thinking (note my edits to my post), but seems odd that it would read normal temp. and supply heat with the thermostat stuck open. If it was stuck open, wouldn't the car never get to proper temp. even at idle as the thermostat is already open?

+2 for the cooling system overhaul if you don't know if/when it was done! No need to be stranded on the side of the road, or overheat the engine due to a cooling system failure.

When my thermostat was stuck open on my old e46 that's exactly how it acted: normal operating temp at idle or low speed driving 10 o'clock position on the highway or higher speed driving.

On cold days it took a long time to get up to temp.

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[Pip]

In my head it also makes sense because of the engine rpm. At idle the water will warm because it isn't doing much while under load the water pump is moving the water around and it is cooling. At least in my head it makes sense.

[kayger12]

In my head it also makes sense because of the engine rpm. At idle the water will warm because it isn't doing much while under load the water pump is moving the water around and it is cooling. At least in my head it makes sense.

Also have more airflow over the radiator the faster you drive versus very little to no airflow at idle.

[brettbimmer]

When my thermostat was stuck open on my old e46 that's exactly how it acted: normal operating temp at idle or low speed driving 10 o'clock position on the highway or higher speed driving.

On cold days it took a long time to get up to temp.

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Thanks Keith. Not trying to beat a dead horse with this - just trying to figure out what I am missing when thinking about the cooling system in my head. I guess in my mind I was thinking that the thermostat was stuck open all the time to allow max coolant flow, but it must be that it is going from closed until initial warm-up to max open, which is not allowing proper operating temp? If this is the case, then I suppose that "stuck-open" is a bit misleading, but everyone uses the term.

I get that the added speed of the water pump would speed up the coolant circulation as RPM's increase, and that the added airflow over the radiator would help to cool the engine too, just trying to mentally figure out what I am missing here.

[slater]

thanks for your collective brain-busting here, guys. as of today i am out of town for 3 weeks (ZHP is tucked away in the garage), so i won't get a chance to work on it until march. new t-stat and other PM parts will be on order soon. :)

peter