Kent and Kaia, Thank you again for your help! Just replaced my upper and lower radiator hoses in my 1982 300SD Diesel, refilled the car with Mercedes coolant and took her for a drive. Holy toledo. Scary temps almost instantly on the highway. At idle, the needle is at 88, on the highway, the needle regularly made contact with the line between 80 and 120, and then at one point, rose up exactly 1/4 to 120. Completely weird. The only thing I did was to change the hoses; the needle was rock steady at around 86/88 driving back from Colorado to Maine. I can only think that there might be an air bubble. Any help on properly purging this would be greatly appreciated. Annoyingly, the heater motor is still kaput, so I'm not sure I'll be able to cycle this to help alleviate things. Best regards, -James F. Smith