Closed cooling set-up:

Running on the hose, should oil temperature begin to climb some with coolant temperature? Running on the hose for 20 minutes, I’ll see coolant temperature at 170, and oil temp of 150-160. Both engines. Verified pan temp with IR (154-157). I’m pulling the oil temperature from the oil cooler port next to the pan rail (Gen VI block). I’m using a thermostatic cooler, Hardin 625-700 (the one with the bypass tube/thermostatic plunger/cutoff).

First I’ve messed with closed cooling so just curious more than anything.

I think mine is in that ballpark on the hose, like around 150. (I actually run it in a large tub for the outdrive) You can put your hand on the inlet and outlet oil fittings on the oil cooler and really feel a big difference. I was kinda surprised how warm the oil felt going into the cooler the first time I touched it.

I didn’t think to check the cooler inlet and outlet.

Good to know they’re about the same. Are you closed cooled too or raw water?

Running on the hose, the engine is not under any load and the oil shouldn't get hot.

Should have clarified the environment a little more.

The engines were run in the water (but no load) for a half hour. Engines are new and we dipped the boat to check for leaks while swapping trailers (I’m replacing all the brakes). Once we got back to the house, I put her back on the hose and noticed some residual temperature left over. Ran another 20 minutes and that’s what I got (just about 160 degrees).

The oil probably had some heat soak.

Running on the hose the weekend before, temperatures were 150 on the house after about 30-45 minutes (fresh starts).

I think the closed cooling system retains a lot of heat. Similar to automotive.

the oil is not getting hot, it is just transfering heat from the block and heads to it. that is why it is close to the same as the water temp. when under load and working the oil pulls heat from the valve springs, friction and piston heat that are all way hotter than idle so it is higher than the water temp. I would worry if the oil temp was higher than water temp at idle as that would mean there is a lot of heat coming from something other than the big chunk of iron sitting there.

I'm closed cooled too. Has a Whipple on it but that probably doesn't make any difference in this situation.

Mine stays at 140 on hose. never moves