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.

[DDK's 525]

I just replaced my heater core and radiator (don't ask how I screwed the radiator up. stupid plastic ) and I used this bleed method from the bmwE34 website after the bentley meathod did not work for me.


Quote:
M20 Bleeding experience by moots:

Just to share a simple method to bleed the cooling system.I really cannot comprehend why we need to bleed,bleed and re-bleed the cooling system after every maintenence.I did this after replacing the thermostat and flushing the coolant:
(Mine's an m20 engine with the reservoir by the side of the rad)
1.Fill up the rad with the plastic bleeder screw(on reservoir) and metal bleeder screw(on t-stat housing),open.
2.When full,put a finger over the reservoir bleed hole and blow,yes,blow into the reservoir filler neck.(we are basically pressurising the system)
3.When water flows out of the t-stat housing bleed hole,tighten the screw.
4.Top up reservoir if required.
5.Now blow again until coolant exits the reservoir bleed hole and tighten when bubble free.
6.Top up coolant to the cold/kalt mark,tighten cap.You're done. No more bleeding required as all air is purged from the system. I have done this 4 times on three cars and it worked like a charm.



But I modified it a little. Instead of blowing in to the tank, I used my compressor turned down to 10psi. I used the blower nozzle and zip tied a 5"-6" piece of bicycle inner tube to it. I then stretched it over the fill hole and pressurized the system and followed the procedure above. It worked great the first time

Btw, I have an m20. Don't know if it will work on any other engines.

[Rick L]

I just took my car to local mechanic who works on BMW. After all the time I spent trying to figure this out and different ways to bleed the air out, it turned out to be just that. AIR IN THE SYSTEM! He use a pressure system to flush out the air and my car is back to normal… Temp gauge right at the center and hot air from heater is back! :) Thanks everyone for your help! However, my coolant lever sensor still goes on when I start my car. I replaced that too when I replaced the radiator. Is there a way to test the sensor? Or the wires that connects to it by shorting it or something?

[whiskychaser]

Glad to hear you got it sorted:) I think the level sensor is a simple 'make' switch. Test it by unplugging the connector and put a meter across the sensor terminals. You shouldnt get a reading as the switch should be open. If the coolant low message is still on with the wiring unplugged, the fault must lie in the wiring

[Rick L]

Thanks for the info... I found the coolant level sensor problem. There was a cut in the wire under the air box. Got that problem fixed but break something else in the process of tracing the coolant level sensor line. Anyone know what that piece is that is attached behind the air box with two small coolant hose attached to it? Tip where one of the hose connects to broke off but it's only the tip so I have enough connector part to clamp the hose on with hose clamp but like to replace that piece. Anyone know what this is?



Glad to hear you got it sorted:) I think the level sensor is a simple 'make' switch. Test it by unplugging the connector and put a meter across the sensor terminals. You shouldnt get a reading as the switch should be open. If the coolant low message is still on with the wiring unplugged, the fault must lie in the wiring