I was wondering if a thermostat is mostly just to keep the coolant from going to the radiator until the engine is at operating temperature, or if it opens and closes frequently.

I just noticed when I pull a trailer I get up to 90* and that's only about 5 or 10 minutes at 60MPH. I know my thermostat is a little hotter than the normal one because the PO replaced it so that his coolant would be hotter for his veggie conversion. If I drop back down to the normal thermostat, will the car stay cooler while I tow my trailer?

(my normal operating temp is about 85* with this thermostat. the PO says that before he changed the thermostat it only ever got up to about 65*, but I am not sure if he is credible on that)

any advice? Summer is coming and i don't want to get caught with my pants down.

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1985 MB 300D/T

Fell off the WVO bandwagon when people started trying to charge $2.50 a gallon for dirty vegetable oil.