Running thinner oil raised temps?
 

Hi guys, it's been a while since I have posted here, 2 jobs does that I guess :/.

Anyway, I finally got around to changing my oil after 9k miles (uhg) and I went from 5W-30 to 5W-20 and my engine temps went up 20F? I don't remember ever hitting 235F at night while driving home from work, and now I sit there for most of the drive. Also I run full synthetic if that means anything. I have some 5W-30 left of the same brand so I was considering putting some in to raise it but, I would like some input first.

The original Toyota recommended oil is 5w-30. Unless it was back spec'd, I would not use anything less than 0w-30 synthetic oil. (5w-30 if using dino) The 2nd number (30) should never be lower, especially if you are using grill blocks.

Your cooling system should be able to handle all sorts of variables, I haven't heard of different oils causing temp changes. It seems plausible, because increased friction would raise temps. But think about all your engine can do without temp fluctuation. If you decided to drive at double the normal RPM, or if it was 100 degrees outside. The temp still stays roughly the same, and should stay in a normal range especially on the highway with max radiator air flow.

Going to 0w20 hasn't changed my engine temperature. Maybe the oil is flowing faster and picking up more heat. Are your pistons oil spray cooled?

I wouldn't go to a 5w20 even if my engine was back spec'd. Stick with the 5w30, your engine will run as it did before and your fuel economy will still be the same as well.

I have run 5w20, 5w30, even 5w40 and never noticed any fuel economy changes that I could even hint at.

what is your climate like? last time I had an issue with temps that high i had a bad pressure cap. Come to find out, they are a typical wear item and cheap to replace. Try that first, if that doesn't help id suggest putting some Seafoam in the oil and changing back to the usual oil after a tank.

The reason your oil temp rises like that is that you need to use heavier oil or add an oil cooler. Turbo and forced induction owners need to watch oil temp to get a better gauge on engine load/wear.

Too warm temp will separate your oil and kill your engine.

After 9000 miles the old oil 5w30 could have been thinner than the new 5w20 oil.

Original radiator?

regards
Mech

1/3 of engine heat is removed via the engine oil, I would never go thinner on an older motor.