Well another day in the running hot 500. This morning, it was 56 deg ambient when we left. Went the same route we had been before. 10 min to interstate, about 10 min on interstate at 65 mph. Temp started up. We timed it with a stop watch and started timing when the temp went over 200 F until it went back down to 200 F. 16 seconds. It topped out at 216. Then stabilized at around 185. Talked with a friend who works at a Mercedes/BMW independent shop. He said they had seen this before on a few cars and just decided it was normal for some of these older cars (Mine will be 30 years old this coming November). Well, I am not giving up that easy. I didn't do it a year ago and shouldn't do it now. My son had a problem just like this on a 86 (?) Peterbuilt long nose with a Cummings engine It had 2 thermostats, one for bypass and the other for flow through radiator. Turned out there was a part number change in the bypass thermostat. The new thermostat didn't have a bleed hole that would allow some hot water to get around it to heat up the working part of the valve. He made a small hole in it, and fixed the problem. He found out later that Cummings found out about the problem and fixed it by putting the hole back in it. Well, I just drilled a hole in my thermostat so some hot water could heat the element quicker. Worst thing that can happen is it will take longer for the engine to warm up. I think the spike in temperature is between the time the thermostat starts to open and the bypass is closed. I have gotten my R&R time down to 35 min.
I'll let you know either way.
If anyone has access to the MB parts manual, could you please check to see if there was a PN change in the thermostat for a 1984 500SEL in the last few years.
Thanks

Paul

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84 500 SEL (307,xxx miles)