Coolant Temp / Check Engine M50

[Russ in Seattle]

When driving our '95 525iT home last night the OBC suddenly beeped and the Coolant Temp warning came on. Temp gauge was pegged to the right. I was able to pull over and let it sit for a couple hours. We retrieved it and drove it the rest of the way home (approx. 5-minute drive). This time the engine seeemed to warm normally and temp gauge stayed in middle even during idling in the gragage for 10 minutes. Upper radiator hose got hot; lower one remained cool. What gives? Stuck thermostat? Coolant pump? I just changed the oil (my first time on this car) but the oil level is fine with no apparent leaks. Could I have done something stupid?

[AllanS]

I would say a stuck-closed thermostat. Very easy and inexpensive to replace, although this can't be said for it's possible result (overheating).