Overheating

[JGood]

Thanks guys. I didn't replace the pump or the thermostat when I put the engine in, and it's a high mileage engine, so I'll just order both.

7pilot, do you recommend the composite or metal pump?

I have some water wetter left over from my track car, not sure why I didn't think to throw it in this car. Will do.

[Jand3rson]

Did you renew the water pump when the engine was swapped into the E30?
Without trying to teach you to suck eggs there are 3 water pumps with different impellers.
1, the bad plastic impeller version.
2, the metal impeller version.
3, the composite impeller version.

I suspect your water pump. When I had my M50 apart before I put it in, before just ordering a new one willy-nilly, I checked mine. It's the metal impeller version, which means it was replaced at some point, and there was no shaft play or anything, still spun very freely, so I just went ahead and kept it as-is. I'm using the M42 radiator and thermostat-controlled electric fan, too.

[blackhawkimpact]

Mines does the same thing. But it doesn't actually overheat just the gauge rises on idle even if the both fans are on

[7pilot]

Did you renew the water pump when the engine was swapped into the E30?
Without trying to teach you to suck eggs there are 3 water pumps with different impellers.
1, the bad plastic impeller version.
2, the metal impeller version.
3, the composite impeller version.

It is possible that the thermostat is sticking in the partially open position.

I'd recommend a water pump and thermostat change.
I'd also throw in some Water Wetter to prevent "microboiling" in the head.


m

[JGood]

Car is an 85 325e, cammed m50b25tu, m42 rad, thermostat controlled electric pusher fan. Newer fluid, verified the fan is kicking in and working fine.

If the car idles for more then 5 minutes with temps in the 80's or more, it overheats, even with the fan running. When I start driving the temp drops right away back down to normal levels.

It never did this before in ~3 years and ~40k miles, and I haven't changed anything.

Haven't touched the coolant level in months, so it's not leaking.

I never messed with the thermostat or water pump, but I'd think those would cause major issues if they failed... not just this idle overheating issue?