The OFFICIAL let's make Erick's M30 stop overheating thread

[Danny]

Just because something is new doesn't mean its good... just sayin.

[Erick]

The pump was replaced before I pulled the motor out, but only just. It had less than 100 miles before I did the headgasket.

[ForcedFirebird]

How old is the radiator?

The entire system has been pressure tested at my shop, everything checks out. New head gasket, new hoses, new radiator, I'm sure Erick put a new pump in when he had the motor out, something weird is going on.

[Erick]

Brand new.

[Jean]

How old is the radiator?

[Erick]

^ Seems like you were right, for the most part. With the M30 coolant cap, it does seem like the temp cools down faster once you start driving again. However, that being said, if you still leave the car at idle, it will eventually overheat. (I timed it from 175 to 210 in 7 minutes at idle)

[LowR3V'in]

m20 vs m30 cap won't matter.
That's not going to cause your overheating.

[LowR3V'in]

m20 vs m30 cap won't matter.
That's not going to cause your overheating.

[Erick]

I have not tried yet. I should hopefully pick up a new cap tomorrow morning.

[cepa318is]

did replacing to an m30 cap fix the problem?

[ForcedFirebird]

Are you using a stock M20 1.4 bar radiator cap? It'll let go earlier than the M30-appropriate cap, which is 2.0 bar. Lower pressure = less cooling capacity.

I also agree with ForcedFirebird, try a lower temp t-stat like an 80°C, and drill a little hole (like 1/8") where the arrow points to ease the bleeding process. 71°C and 75°C are also readily available and cheap, but generally, you want to keep the t-stat temperature high as possible without overheating to avoid prematurely wearing your engine and to promote good combustion.

With an 87°C thermostat, it's not surprising you're seeing 190°F water temps. The thermostat is attempting to make your engine run at 87°C, which is 188.6°F, so if anything, it's working as advertised.

This makes perfect sense! It was racking my brain that Erick was using the entire cooling system from the m30, minus the fan, and it was still acting like a slow leak. I pumped the system to 15psi and it held, so hence the confusion. I also suspected a bad cap, but we tried another cap with the same results. Also mentioned the same to Erick yesterday about the t-stat rating, I did the math quick in my head and figured it was about 190*, which is high for the kind of driving the car will see during it's intended purpose.

[FredK]

Yes, a late model M30 cap (E34) will thread right into a late model M20 expansion tank.

PN 17111742231 works on a TON of other BMWs, including the E30 318is, E36 325i/M3, Z3, Z4, etc.

I didn't notice I had the wrong cap until I heard hissing after cooling down at a HPDE in hot weather. I heard some hissing out of the cap and was wondering what was going on. I'm also running distilled water and Water Wetter.

[Erick]

Thanks Fred. I spoke with John yesterday over the phone and I am going to try to run the car without a thermostat first.

As for the cap, yeah, I've been running the M20 one. I am not sure if the M30 one will thread onto the M20 overflow tank, but I am willing to test it out.

- E

[FredK]

Are you using a stock M20 1.4 bar radiator cap? It'll let go earlier than the M30-appropriate cap, which is 2.0 bar. Lower pressure = less cooling capacity.

I also agree with ForcedFirebird, try a lower temp t-stat like an 80°C, and drill a little hole (like 1/8") where the arrow points to ease the bleeding process. 71°C and 75°C are also readily available and cheap, but generally, you want to keep the t-stat temperature high as possible without overheating to avoid prematurely wearing your engine and to promote good combustion.

With an 87°C thermostat, it's not surprising you're seeing 190°F water temps. The thermostat is attempting to make your engine run at 87°C, which is 188.6°F, so if anything, it's working as advertised.

[Erick]

Might as well just pull the t-stat out.

Glad to hear the neck is doing better!!