I almost overheated a few days ago and I discovered I had a bad fan clutch - it had no resistance and was barely turning. After replacing, it seems to work as it comes on and spins at quite high speed now — however, it still tries to overheat. I have been very careful to not let it overheat but it has started creeping over. I decided to replace both the thermostat and water pump and have the parts now. However, I decided to try something to see what happened. I opened the radiator cap and started car. When car got to about half way on thermometer and sat there for a while, the coolant did start having activity as in some shooting up and out until I turned engine off and got cap back on. Doesn’t that mean
that the thermostat is opening and the water pump is working? I have no loss of coolant at
all since this started happening. What else could make it overheat?
One other thing to note - with the new fan clutch, as soon as car is started, the fan does kick in and runs on what appears to be high spied. Isn’t it supposed to be slower until it engages? Could the sensor in the
lowwe belt be bad and cause this? It would make sense to me though that even if it’s bad and causing fan to run on high, that it still wouldn’t overheat.
this isn’t my only car but I love the car and want it in running condition and not trying to overheat. I do like to drive it some. Thanks guys!
It means that your cooling system is always supposed to build some pressure when it's reaching operating temperature, which doesn't happen when the cap is off.
The fan clutch always has a bit more grip on the fan on cold startup. It spins faster, but loosens after some 20 seconds or so. That's normal.
Belts have nothing to do with the clutch-fan, as it's turned by your crankshaft.
Since you already have the thermostat and waterpump, I'd put those in place and see if it's fixed.
Well done on not letting it overheat. Use your cabin heater on max hot and full blast to extract heat from your coolant if needed.
Make sure the fan shroud is in place as well by the way, as that maximises the efficiency of the clutch fan pulling air through your radiator.
What car is it about though?
The E46 mechanical fan is attached to the water pump via a left hand thread. So, a slipping belt would impact fan speed. That’s not your problem. Your problem is that you need to properly bleed the cooling system. The M54 (your engine’s designation) can be a bear to bled properly. Go to E46Fanatics and check out Mango’s sticky on the cooling system.
So you don’t think I need the water pump and thermostat possibly? Just bleed it?
This link explains an effective bleeding procedure.
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My friend who is a mechanic who is helping me out seems to think the water pump and thermostat are ok because of the fact that with the radiator open, it circulated the coolant after the car warms up - thermostat appears to be opening and the pump appears to be pumping. Anyway, we did the process to bleed the coolant system and it seemed to take a much longer time but it did start to overheat again. Any other ideas? Is it possible it’s still the water pump or thermostat and I should go ahead and replace or is there something else? Could it be the sensor in the bottom hose? The fan clutch is working and turning fast but maybe it should kick in and turn even faster? Also, should the aux fan only run when the AC is on? I don’t see mine come on unless the air is on but I don’t think it has anything to do with problem. I’m about to lose my mind - lol. Also, I live in a very small town and there isn’t anyone who works on there cars professionally - no dealership for bmw or anything. All ideas welcome!
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Should I try to bleed a second time too?
Any ideas, guys?
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