Overheating issue… HELP!

[Rick L]

I just replaced the radiator and thermostat in my car and it is overheating now. I tried bleeding with extension tank cap off and also the bleeder screw. But still overheating… I swapped the old thermostat back into the car (thinking the new might be bad) but still the same. My car will go past the ¾ mark in temp gauge driving (so can’t be fan clutch) or just parked. I’m puzzled why it’s overheating. Before the radiator + thermostat change, my car was running very cool (only at ¼ mark in temp gauge when driving but ½ mark when parked). I replaced the radiator after noticing a slight crack by the upper hose. And almost forgot that when I turn on the heat, it blows cold… Any advise or info is appreciated.

[e34.535i.sport]

Did you leave the heater controls on full temp while bleeding - and do it up a hill etc? I leave the filler cap on when bleeding the system, never had a problem...

Water pump working ok?

Mine was similar temperature wise when the thermostat had gone... Changed it for a new one and it sorted the problem.

[pingu]

Good point, could the pump be duff?

[Rick L]

No issue with water pump before the new radiator and thermostat so likely it isn't that. I can't believe both thromostats are bad (old one always ran cool). I never had overheating before the new radiator and thermostat change. I'm not sure what you mean by up hill?

[e34.535i.sport]

No issue with water pump before the new radiator and thermostat so likely it isn't that. I can't believe both thromostats are bad (old one always ran cool). I never had overheating before the new radiator and thermostat change. I'm not sure what you mean by up hill?

Parking the car on a steep incline makes any residual air bubble travel to the highest point of the system (near the bleed screw) easier so you can bleed more effectively. Drive it onto a steep hill facing upwards, leave the engine running and release the bleed screw slowly until it flows bubble free then re-tighten the screw. REpeat this many times until you're sure its all out. With the heater dials on full heat and I had the blower on number 4.

You said your car was running too cool with the old thermostat this would suggest it was staying open... Then overheating with the new one (staying closed)... One way to check is to start the car in the morning with the new thermo in (make sure the car is fully cold i.e sitting all night) and run it and see if the upper radiator hose stays cold even when the car has reached operating temp. This way you will know its the new Thermo causing the issue and replace it!

Let us know how it goes or if you find the fault or if you need anything else!

[Rick L]

Thanks for the info. I tried everything and still overheating. Could the new radiator be bad??? That's most unlikely but I'm kind of stumped why it is overheating.

Parking the car on a steep incline makes any residual air bubble travel to the highest point of the system (near the bleed screw) easier so you can bleed more effectively. Drive it onto a steep hill facing upwards, leave the engine running and release the bleed screw slowly until it flows bubble free then re-tighten the screw. REpeat this many times until you're sure its all out. With the heater dials on full heat and I had the blower on number 4.

You said your car was running too cool with the old thermostat this would suggest it was staying open... Then overheating with the new one (staying closed)... One way to check is to start the car in the morning with the new thermo in (make sure the car is fully cold i.e sitting all night) and run it and see if the upper radiator hose stays cold even when the car has reached operating temp. This way you will know its the new Thermo causing the issue and replace it!

Let us know how it goes or if you find the fault or if you need anything else!

[Washburn]

I had same symptoms. Running cool since I owned it. Had an indy flush it all out while putting in a new thermostat. Ran great until a week later when the water pump toasted itself. I don't know, but maybe the flushing had something to do with it finally failing. They are cheap, easy to change, and it's going to go sooner or later anyway...that would be my recommendation.

[duckloads]

when I recently replaced the water pmp and T'stat in my 535i, the T'stat was marked with an "up" indicator. That is so you can bleed the air out.

To bleed the air out, I filled the system with engine off and bleed screw open and let "a lot" of coolant out of the bleed screw hole. Close screw. Start engine, and the heater controls must be set to fully hot. Allow enough time for coolant to get hot and pressure to build. Shut off engine. open bleed screw to expell air and coolant untill all pressure in system is bled off. close bleed screw and start engine to heat / build pressure again. repeat 3-4 times.


good luck

[whiskychaser]

If your car overheats before your heater gets hot its almost certainly got air in the system: the coolant circulates to the heater before the stat even kicks in. In theory you bleed it with the cap on and the bleed screw on the rad open. In practise, run the engine at fast idle then open the bleed. But if that needle creeps past 12 o'clock stop the engine, then open the bleed screw but be careful of the steam that comes out. It can take an hour to get it all out so be patient. Dont top up with cold coolant mix-heat the 50% water before you put it in. Cold coolant + hot engine is not a good combination

[525i winter driver]

I tried everything and still overheating. Could the new radiator be bad??? That's most unlikely but I'm kind of stumped why it is overheating.

hey this might be really too simple but when i was trying to bleed my rad i did something stupid and got a whole bunch of air in the system - had similar symptoms (cold air, strange temp) for a short time which went away by themselves while i was tooling around but the culprit the whole time i think was the lower hose from the rad to the water-pump... it was ever so minor i thought they were on good and tight but it might be worth a quarter-turn on the clamp at each end? i was really stumped myself, thought it was the bleeder valve or worse hg again.