Overheating, Please Help!

[Midweste30]

I have an s50 I just swapped in my e30 and its overheating horribly. If I let the car idle the temp will be normal but if I drive the car for anything longer than 5 minutes even at 25 mph it will overheat. Has a new radiator and spal fan hooked up. Bought it from a BMW speciality place who replaced the head gasket waterpump and thermostat then the e36 m3 was rolled so they pulled the motor and sold it to me. They did not have the head decked when it was off though which seems odd to me. Ran compression and all cylinders we're between 180-200. Could it still be head gasket? Bled the system to no avail, even tried a different radiator. Going to try a different thermostat and see what happens. Any ideas as to why it could be overheating. Hoping to run leak down soon if I can find a tester local so I don't have to buy one. Please help! Thanks

[R1dd1ck913]

What temp sensor did you use?

[Midweste30]

What temp sensor did you use?

M20 sensor I'm fairly sure

[DesertBMW]

If I let the car idle the temp will be normal but if I drive the car for anything longer than 5 minutes even at 25 mph it will overheat.

This is typical cracked head symptom and it is very common for these heads to develop a crack from intake valve to one of the coolant ports. At idle it is all fine, meaning thermostat is opening, water is circulating, radiator is doing it's job. But when you drive it compression is higher, there is load on the engine, compression is pushing air trough the crack into cooling system, you are getting air into cooling system and it cant circulate properly.

[Midweste30]

This is typical cracked head symptom and it is very common for these heads to develop a crack from intake valve to one of the coolant ports. At idle it is all fine, meaning thermostat is opening, water is circulating, radiator is doing it's job. But when you drive it compression is higher, there is load on the engine, compression is pushing air trough the crack into cooling system, you are getting air into cooling system and it cant circulate properly.

I forgot to mention when I posted this is that when we let it idle then revved it up and it got hot only half of the radiator was hot on the drivers side. The other half was completely cold like coolant wasn't running through it at all. Then I took it out and ran water through it and it wasn't clogged or anything if the sort

[ThatOneEuroE30]

Sounds like maybe your thermostat isnt opening or your water pump isnt circulating coolant

[M3PO]

This is typical cracked head symptom and it is very common for these heads to develop a crack from intake valve to one of the coolant ports. At idle it is all fine, meaning thermostat is opening, water is circulating, radiator is doing it's job. But when you drive it compression is higher, there is load on the engine, compression is pushing air trough the crack into cooling system, you are getting air into cooling system and it cant circulate properly.

I just want to point out that compression is fixed. Static compression is a characteristic of the engine and dynamic compression is related to the cam. However, cylinder pressure can rise with RPM due to momentum effects created by the air rushing into the engine.

[Midweste30]

Faulty Themostat!

[E30Nick325]

You can get water through a radiator and it stll be clogged. It's best to take the radiator into a shop that can test it if you suspect it could be faulty.

[DesertBMW]

Faulty Themostat!

if the thermostat is always closed then it will overheat during idle also, you said it does not overheat during idle