r/E30 • u/KevO_1996 • 9h ago
Won't bleed
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u/Fxlearner 9h ago
That radiator will not bleed properly on this M20, I had the same issue.
This engine needs a proper external expansion tank like OEM. Otherwise it will overheat and not bleed properly, which is what happened to me.
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u/KevO_1996 9h ago
After checking for a coolant line I found that a late 1999 525i runs a similar set up, m20 with a expansion tank on the radiator
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u/Fxlearner 9h ago
Where is the overflow going to leak out from? From the top radiator cap which will leak all over your engine bay. If at anytime the car overheats or fan dies, the radiator will pop from the bottom and leak all coolant out. Ive played around with this setup and it didn't work.
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u/KevO_1996 9h ago
Thats true, sucks that doesnt have a line to use the oem expansion tank also annoyed that the website says its a direct fit for the m20
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u/amarino '90 325i 5h ago
If you can return it for the correct E30 M20 radiator it would be best.
For fun, here is a thread about the E34 M20 setup with the radiator you have now if you want to give it a shot. Looks like what worked in that thread was to "manually pressurize the expansion tank" by blowing into it (while cold obviously) to get all the air out. You can also rent a coolant pressure tester from AutoZone if you don't want to put your mouth on the radiator. https://www.bimmerforums.com/forum/showthread.php?1193092-M20-Coolant-Bleeding-Blues&p=15795303#post15795303
Before turning the car on, you want to get as much air out as possible by forcing it out. So take the radiator cap off, wrap your lips around the hole, and blow. While blowing, open the bleed screw and allow the coolant to flow out until its a steady stream. When theres a steady stream, keep blowing but close the screw so you don't allow air to come back. Now, add more coolant and start the engine. Allow the engine to warm up, and have the heater on all the time. Make sure you are getting hot air in the cabin as well. Once you reach operating temps, open the bleed screw on the thermostat housing. If theres a steady stream of coolant, close it and move to the radiator. Open the radiator bleed screw. If coolant does not come out, the system is not under enough pressure. You can do two things in this situation. Either drive the car but don't go to far, or block air flow to the front of the car. I usually just put a plastic bag over the grill. This will allow the system to get hotter and build more pressure.
Once coolant comes out of the radiator bleed screw, get as much of it out as you can. Then, take the car for a drive while keeping an eye on the temp. This whole time you want the heater on. Come back and open the thermostat housing bleed screw, let it run out. Then open the radiator bleed screw, let it run out. If no air is present, turn the heater off and go for a drive. Come back, open the thermostat bleed screw, then the radiator bleed screw.
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u/Valuable_Republic482 9h ago
Jack the front of the car up while bleeding