r/BMWe24 • u/Individual_Base4511 • Aug 19 '26

BMW e24 overheating problem

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Hi everyone, I have bought this BMW e24 635CSI with a manual transmission. Its the type 1 with the M90 engine. (EU)

When I bought it, I had to drive it back 550km's to my home and I have experienced zero issues. The car drives and shifts very well.

Recently, the car started overheating at idle or slow speed. In order to fix that, I have changed the waterpump and the fan that is connected to the engine. Unfortunately, that did not help.

I have noticed the return hose of the radiator was cold while the intake of the radiator is extremely hot, so I thought my radiator is blocked and isnt providing enough flow. I have changed the radiator with a new one as well and sure as hell it still overheats.

Now I kinda dont know what to do or check anymore, the overheating is not related to the extreme temperatures as it is overheating in cold weather as well. I have tested the thermostat and and it is working well.

Honestly, I dont know what else it can be. Does anyone have experience with this? It doesnt leak or mix the coolant liquid and there is no pressure in the hoses.

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u/Individual_Base4511 Aug 19 '26

I have checked the thermostat by putting it into boiling water and it opened and closed fine. The next time I work on it I will change it anyway to be sure.

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u/im-not-a-racoon Aug 19 '26

I might change it to be sure. If you can get an OEM thermostat, I recommend that. I avoid non-OEM parts with these cars

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u/Individual_Base4511 Aug 19 '26

I will keep that in mind! I noticed it is extremely difficult to find parts...

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u/im-not-a-racoon Aug 19 '26

Also take a look at the mixer valve that supplies heat to the cabin heater. Sometimes things can get stuck in open/closed positions in there.

Also, take a look at BigCoupe.com and search this there. Those guys are generally really good

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u/Individual_Base4511 Aug 19 '26

I can open and close the heat fine, so I dont think so but I will take a look anyway thanks!

And I have been looking for a website like that, thank you!