Glad to see this problem is isolated to a few of us at least.
I got a new radiator that I have filled and bled properly and it doesn't seem to have cured the problem as much as I thought it would. My other m42 barely gets to the 1/2 mark and this one seems to love sitting at the half mark. This means the car will easily climb past half once again when the flogging ensues.
The e30m3 cluster is almost plug and play save the wire for the oil temp sensor. My oil temp sensor is tapped opposite of the oil pressure sensor and then run to the cluster. The sensor on the drain plug seems a little fragile to me as well
It's a blessing in disguise - this oil temp gauge - as I am very well aware that hot oil and hot water temp is a no-no

and more credible than the stock water temp gauge alone.
I'll take the car for another shake down and probably try a colder thermostat next weekend time permitting. I have a graf water pump and I am almost tempted to get the next brand out there to see if that may help any? The aux fan works on high and low speeds as well. I am thinking a puller fan in place of the fan clutch might be the next simplest approach. I'd run it separate of the aux fan though and manually activate it with it's own power via a fused line.
Needless to say I have been checking my oil and radiator for traces of a frothy mix in anticipation of the worst reality of any vehicle owner -- t3h cracked head mod -- :rolleyes: