I have had thermostat problems too. My thermostat that the car had when I bought it started to fail and kept temps from exceeding 60 degrees C. I replaced it with a new one and it would seem to hold temps at 85 degrees C. The previous one used to keep temps at just above 80. The new one started to fail recently and its not even a year old. If I keep my heater on full blast I can still maintain about 83 degrees C temps in the winter. If I turn it off however the temps slowly climb to 100C. Temps rise to the 80 degree range quickly then creep up slowly from there.

I have bought a new one from napa. Last night I drilled 3 3/32 holes around the edge in the new one. This will provide some flow but it won't interfere with warm up much.

I do have something to say that I haven't seen stated here yet. If you have an engine that has run at 80 degrees C all its life and you change thermostats to one that causes it to run at 90, it will cause excess wear due to thermal expansion. You want a thermostat to hold a temp closely no matter what to limit this.

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green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

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