1996 auto sport 4.0
so i changed my oil today and i usually run 10w30 but i was interested in trying 15w40 after reading some things on here. so i put rotella 15w40 in. so heres my problem my jeeps running a whole lot hotter like 30 degrees hotter now. my usual is around 200-210 and now its hitting around 230 and i seem to have some power loss when accelerating.
why did changing the oil do this and should i just swap back to 10w30?

 

Changing the oil shouldn't make it run 30 degrees hotter however, all else being equal, thicker oil runs hotter due to increased resistance to flow. Something else caused a 30 degree coolant temp increase.

 

I am flushing the radiator tomorrow maybe that will help. But I have changed nothing else and probably change it back

 

+1.

 

i just went from 15w-40 rotella back to a 10w-30 and haven't noticed a change in temp but have noticed a huge difference in gas mileage.

 

Yeah I know the oil shouldn't change the temp but its the only factor in play I haven't changed anything else

 

Better or worse mileage?

 

Coincidence...

 

Something, other than the oil, changed.....ambient temp, driving conditions, cooling system component failure, gauge/sending unit wacked, something.

 

I agree. There is no way that your oil change to Rotella by itself has resulted in a 30 degree coolant temperature change.

Something else is going on.....start by verifying that temperature by pointing an infrared point and shoot thermometer directly at the thermostat housing of a hot engine.

 

waaay better; definitely noticable at half tank. I'll have a better figure in the next two days as my tank runs down.