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My water temp (fan off) runs about 205-210. Thats with the 203 state in there. When I was running the stock thermostate I'd run 180 with the fan back in.
As far as a range, I'd say keep your water temp below 230.
180 with a 203 stat is not good. something is wrong with either the gauge or the stat. You should be running a rock solid 200-205. Like Farm said oil temp will be close or a little higher than oil temp.
As for range of temp, oil temp will move more than coolant temp. My coolant never changes plus or minus 205 unless I idle for a while but running down the road no matter speed or load its between 200-210. But like Farm said anything under 230 should be fine.
Fan clutch really should not have the much affect on it. Is the stat works as its designed there should not be any coolant flow to cool if the truck is not at the correct temp.
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