E30 325i overheating
Posted: Sat May 31, 2025 12:58 pm
Hi all,
I have a 1990 E30 325i, owned and cherished for over 12 years. It's had intermittent overheating issues since last summer that have been investigated and fixed each time, but the problem recurs. By overheating I mean the coolant temperature shooting up - when this happens I'm stopping the car within seconds and getting it recovered.
Prior to the overheating, it last had belts, a water pump and thermostat for good measure back in June 2023. In August 2024 the overheating started, and as the radiator was crusty it had a new radiator and full coolant system hose kit.
Since putting it back on the road this year, it's had two thermostats. The first was "new" but failed quickly and stuck. In Mid-May it had another thermostat, plus an auxiliary belt as the water pump wasn't being driven properly with a loose belt, plus a coolant flush and it ran perfectly - including multiple trips, days and in stop start traffic.
Yesterday after 20 minutes or so of driving, the coolant temperature shot up in a short queue. I stopped, waited for it to cool and ended up getting recovered. Even when out of traffic the coolant temperature shoots up, and the heater and fans on full puts out hot air but doesn't help when moving. Like previous times, the top hoses were hot, the bottom was cold and the coolant had boiled and vented from the expansion tank.
The oil looks good, and there's no mayo residue like what I found years back when I had the head gasket changed in 2015. There's also no smoke - when it's running fine or when it starts to heat up.
As an aside, there's a mouse nest somewhere in the cabin intake / vents as debris keeps blowing through the vents, and I'm wondering if it could be near the heater matrix and contributing to the problem. I'm clutching at straws but running the fan on hot chucks out heat, but it seems to struggle. Thankfully all electrics work and there's no evidence of them inside the cabin or damage, I just need to work out how to clear out the debris from the vents - and put traps in my garage next winter!
I'm wondering if the water pump could have a tight spot. I'm worried it could be the head gasket on the way out, or a cracked head. I'm stumped as to how the car can be fine sometimes and struggle the next, in similar weather and journey types.
Any ideas would be welcome, and if you need any information on the history of my E30 please let me know.
I have a 1990 E30 325i, owned and cherished for over 12 years. It's had intermittent overheating issues since last summer that have been investigated and fixed each time, but the problem recurs. By overheating I mean the coolant temperature shooting up - when this happens I'm stopping the car within seconds and getting it recovered.
Prior to the overheating, it last had belts, a water pump and thermostat for good measure back in June 2023. In August 2024 the overheating started, and as the radiator was crusty it had a new radiator and full coolant system hose kit.
Since putting it back on the road this year, it's had two thermostats. The first was "new" but failed quickly and stuck. In Mid-May it had another thermostat, plus an auxiliary belt as the water pump wasn't being driven properly with a loose belt, plus a coolant flush and it ran perfectly - including multiple trips, days and in stop start traffic.
Yesterday after 20 minutes or so of driving, the coolant temperature shot up in a short queue. I stopped, waited for it to cool and ended up getting recovered. Even when out of traffic the coolant temperature shoots up, and the heater and fans on full puts out hot air but doesn't help when moving. Like previous times, the top hoses were hot, the bottom was cold and the coolant had boiled and vented from the expansion tank.
The oil looks good, and there's no mayo residue like what I found years back when I had the head gasket changed in 2015. There's also no smoke - when it's running fine or when it starts to heat up.
As an aside, there's a mouse nest somewhere in the cabin intake / vents as debris keeps blowing through the vents, and I'm wondering if it could be near the heater matrix and contributing to the problem. I'm clutching at straws but running the fan on hot chucks out heat, but it seems to struggle. Thankfully all electrics work and there's no evidence of them inside the cabin or damage, I just need to work out how to clear out the debris from the vents - and put traps in my garage next winter!
I'm wondering if the water pump could have a tight spot. I'm worried it could be the head gasket on the way out, or a cracked head. I'm stumped as to how the car can be fine sometimes and struggle the next, in similar weather and journey types.
Any ideas would be welcome, and if you need any information on the history of my E30 please let me know.
