You'll notice that I did not recommend the thermostat as the problem. The engine ran at the correct operating temperature under normal loads. It's unlikely that the thermostat won't fully open at higher temperatures...........but, not impossible.

When the engine is very hot (above 100°C)..........shut it down and simultaneously observe the fan. If the fan stops with the engine, the clutch is fine. If the fan spins several revolutions after the engine stops, the clutch is toast.

Right, but someone else did... and it was something he had already purchased by the time I called him - anyway, the Chinese thermoastat does NOT fit , so he's putting the old one back in.

I told him to run the check on the fan clutch, which he'll do as soon as he re-assembles the old thermostat into the car.

He did mention to me that he recalls that earlier today he had parked the car and left the engine idling for a little while and the fan had kicked on moments later as never before... perhaps that's somehow related.

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K