Temperature rising if car is idling or coasting even at speed. Fine if accelerating

[RickT413]

New problem with my beloved 2003 BMW 330Ci. (143,000 miles) As long as the gas pedal is depressed, temperature stays right at 12:00 on the gauge. Perfect.

But once I am idling, or even coasting at 50 mph, temperature starts rising quickly into the red zone (light comes on in the gauge). Today while coasting at 50 mph, the temp gauge was going up quickly. I put the car into neutral and revved the engine. Temperature started going down fast.

Once the temp gauge goes up and reaches the last line before the solid red/lit block, my red oil light comes on. All this happens whether the A/C is on or not. I also note, as I suspect this is a fan problem, that when the A/C is engaged, the aux fan does come on. Main fan seems to be running fine.

At my last oil change my mechanic noted a small coolant leak at the thermostat. But coolant level full today.

Any help would be appreciated.

[328 Power 04]

You should have the whole cooling system refreshed, new water pump, thermostat, hoses, and last but not least properly bleed the cooling system. You may have an air pocket.

Keep in mind, excursions into the red with air pockets WILL damage your engine.

[shadowpuck]

yup, totally agreed - at 143k you are definitely due for a cooling system refresh if that wasn't done recently. if the t-stat is already leaking, it's only a matter of time. don't dare this system to fail - it will and it stands a high chance of melting down the engine.

a cooling system refresh includes at least the following:
upper/lower hoses
coolant level sensor
coolant temp sensor
t-stat (which includes the housing)
bmw coolant mixed with distilled water
expansion tank
radiator cap
water pump
if automatic - fan clutch.

this is also a good time to change the engine belts and pulleys.

[MIKYZZ4]

I agree with both of the above techs,
a system refresh seems to be needed,
as cooling fans don't seem to be at fault.
I suspect that the waterpump is failing,
and if so, the other components can't be far behind at your mileage.
Confirm coolant level is correct and not leaking, causing air pockets,
by first performing a proper bleeding procedure.

[bmwdirtracer]

Of course, everything above is absolutely correct.

Two things I'd like to add though:
DO NOT DRIVE THE CAR!
You may have already destroyed the engine. A single overheat will often warp the head, and pull the threads out of the engine block.

[TonyAngel]

What do you mean coasting? Driving at a steady 50 mph or just taking your foot off of the gas and letting the car coast? Sounds to me like the impeller on the water pump has either lost some parts or is slipping. Whatever it may be, yeah, another for a cooling system refresh.

[ptarditi]

My guess is if your car has a fan attached to the water pump the clutch has gone bad, if its an electric fan its taken a dump or isn't being activated.

[ross1]

I know everybody loves to damn the cooling systems of these cars after a certain age but your symptoms are those of poor circulation or air flow past the radiator*, perhaps just low on coolant. Didn't you mention a leak?
I'm not familiar with your coolant tank set up but strongly suspect coolant is low, maybe check again. A leak can cause the tank to remain full as when the system cools it will suck air from outside rather than coolant from the tank.
* even with a bad fan airflow at 50 mph is more than enough.

And, like has already been said, these engines don't suffer overheating very well.

[shadowpuck]

a leak at 143k on an e46 - it's cooling system refresh time! just part of the experience....

[RickT413]

Please to report the diagnosis. Bad fan clutch and a leaky thermostat. Replacing the Clutch and thermostat today. If this does not fix the issue, will next replace the water pump (or will simply replace the water pump in the fall).

Cost for clutch and thermostat work today $715.


Many thanks for all your comments.

[shadowpuck]

man - labor should be the same to basically finish the rest of the cooling system refresh....hopefully those other parts hold up for you!