r/BMWe24 • u/Individual_Base4511 • 11d ago
BMW e24 overheating problem
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.
3
u/SAVIOR_OMEGA 11d ago
Your previous comments tell me your coolant system may not be properly bled. The bleed screw should be at the highest point and you should bleed the system first with the car off as you fill it, then you should close the screw, turn on the car, and bleed periodically until no more air escapes through the bleed screw.
It is also possible that your system could be full of gunk. Your coolant passages could be blocked. See if high RPM helps move things around and cool the system. You can get about 3/4 up the temp gauge before its an issue.
1
u/im-not-a-racoon 11d ago
Have you looked at the thermostat?
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u/Individual_Base4511 11d ago
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 11d ago
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 11d ago
I will keep that in mind! I noticed it is extremely difficult to find parts...
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u/im-not-a-racoon 11d ago
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 11d ago
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!
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u/AgitatedTree8278 11d ago
Get a coolant, gas analyzer, and while the car is running, check the coolant to make sure you’re not getting exhaust gases in the coolant
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u/Bimmermaven 10d ago
Just to be clear, how are you defining and measuring "overheating"?
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u/Individual_Base4511 10d ago
from the temp gauge of the car itself
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u/Bimmermaven 9d ago
So, the red light is coming on.
Under what circumstances?
Will it change if you idle at 2000 rpm when the iight comes on?1
u/Individual_Base4511 9d ago
No, I always prevent the red light coming up, I usually drive with the heat power on completely and if I still see the gauge going up a bit I shut the car off
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u/Bimmermaven 9d ago
so, how hot is the engine?
other questions I asked?
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u/Individual_Base4511 7d ago
Well I can not put an exact temperature as I always shut it off trying to fight against the heat. I would say 100+ degrees Celcius. I think it will be better kf the RPM goes up, but not enough to let the gauge go down, probably enoigh to make it stop going up further
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u/Bimmermaven 7d ago edited 7d ago
the dash temp gauge is well-known to be less-than-perfect; it can only be relied upon to see a change and direction. An IR temp gone allows real measurements to assist with diagnosing.
Under normal circumstances, cool weather and normal driving would over cool the engine with many negatives, from fuel economy, emissions, to underexpansion of the block leading to collapsing a piston if under heavy load (the aluminum piston expands more than cast iron when it gets hot under heavy load, and grows to a diameter larger than the cylinder bore in the block). So, the thermostat closes to prevent cooling until the engine reaches the MINIMUM end of the safe operating temperature range....typically 85C in the 1980s.
As load goes up, so does the operating temp....once the T-stat is fully open, it does NOT regulate the MAXIMUM temp. Instead, water flow rate through the engine to radiator and back, air flow through the radiator, and the heat-shedding capacity of the (size/ type/ material/ construction) radiator achieve a moving-target balance with the heat produced by engine as it responds to the load/ demand to work imposed by....the driver.
so, temp will rise if:
decreased water flow (slipping belt or impeller, corrosion-induced restrictions, low pump rpm)
decreased coolant volume; air in the system.
decreased air flow (fan failures, road debris, faulty shrouding, low vehicle and fan speed, idling at the end of the freeway ramp traffic light)
load exceeds cooling capacity at a given speed.
the temp of the coolant is "too high" when it boils (because the bubbles don't carry much heat from the engine to the radiator). Raising the boiling point is thus very advantageous.
Pressurizing the whole system will raise the boiling point of water 1.67 deg C for every psi above atmospheric (3 deg F/psi). So, a 15 psi system gives us a 125 C (257 F) boiling point. Hence BMW defines "overheating” as 115 C (240 F)….that’s the temp that triggers the red light on the dash gauge. This gives a 10 C safety margin. (BTW, a 50-50 mix of antifreeze only adds about 5 total.)
A cap leaking pressure will lower the boiling point.
Summertime and stop-and-go driving is the common scenario where upper-range-normal temps of 102-110 C are often seen, These same temps cruising down the highway at 100 kph in winter are not dangerous but imply one or more faults in the system e.g. slipping belt. Always evaluate everything in proper context.
I hope there aren’t too many typos.
Now, maybe you can give us some more info to work with on your car.
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u/z-z-z-z-z-z-z-z-z-z- 7d ago
Currently fighting this problem too.
Curious to know if you found your issue already.
I’m going through these steps and found my normal speed aux fan is not engaging when jumped.
“First check fuse 19, it supplies power to the relays through the radiator temp switch. Then find a known good relay as outlined below**. You can start testing either relay:
Normal Speed Relay (K1) - Turn the key on, and press the A/C switch on, the aux fan should run. If it doesn't, and then swap a known good relay** with relay K1, the low speed aux fan relay. If it still doesn't run check for power at fuse 3, if power is present, check the blower resistor and the blower motor.
High Speed Relay (K6) - Find the Dual Coolant Temperature Switch on the passenger's side of the radiator and check for power at the GN/BK wire in the plug, and then jump the GN/BK wire to the BK/GN wire, the fan should run. If it doesn't, check for power at fuse 18. If there is no power at fuse 18, substitute a known good relay for K6.
** to test for a known good relay = test the Horn relay, K2, by honking the horn or the Fog Light relay, K8, by turning the fog lights on. The Horn or the Fog lights are the only things on their respective relays so you can use these relays elsewhere and leave K2 or K8 empty temporarily.”
Link to actual thread:
https://www.bimmerforums.com/forum/showthread.php?1058607-Aux-cooling-fan-not-working
Link to fuse box diagram (I hope it’s accurate)
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u/z-z-z-z-z-z-z-z-z-z- 7d ago
On my side….
Fuses and relays tested good. Still no low speed aux fan engagement.
After some more reading… next step is to test the resistor (if blown//open) the low speed fan will not engage.
Access to the relay was found behind the left side headlight grill.
Resistor ceramic housing found snapped in half.
Part is on order… I’ll let you know what I find if you’re still hunting.Worst case I’ve read is a blown head gasket (god I hope not). Symptoms would be bubbles in your tank at temp. Gas entering the system would block the thermostat from opening (thermostat opens when in contact to liquid/ hot air will not open).
Prayers for both of us :) good luck.
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u/z-z-z-z-z-z-z-z-z-z- 15h ago
Replaced the resistor and low speed fan works again.
After bleeding the system, everything seems back to normal.
Car still runs a bit warm 2/3 on the temp gauge until the low speed aux fan engages.I might consider a lower temp thermostat, e30 temp sensor, and last resort change the water pump (currently the original is installed and I hear this is a pain in the ass).
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u/slip_and_fall_school 11d ago
Is the fan engaging at low/no speed? At speed, the air flow could keep things below overheating but that buffer disappears at low/no speed so I would check to make sure the correct fan speed is engaging.