I’ve been meaning to post this since I drained my freshly built 565’s for winter. I did a few lake run passes shortly after Labor Day weekend and when recently draining the blocks there was oil in both. Both have new T-stat oil coolers. What threw me off more yet is when draining the water on both - the majority of oil drained first.

I have 6AN hoses joined with a coupler on the top front of the engines for quick draining so was very visible to the eye. Difficult to gauge how much oil was in each but if I had to guess I’d say 1/5th of a quart + - Probably less but again very difficult to know for certain.

I’ll be pressurizing both stat coolers with the stats open or removed but just can’t imagine I’d have two new coolers fail.

Anybody? I haven’t had a chance to pressurize oil coolers yet but again both new coolers defective???

Don't know about oil draining out first, but if the cooler was cracked the oil would be going out into the water and there would be less oil in the motor.

are these closed loop cooling or open?

"What threw me off more yet is when draining the water on both - the majority of oil drained first."

I was under the impression that oil floated ON water..?

Do you have any photos?

Globs of oil ? Or just a sheen on the water ? Or ?????

If it’s a cooler leaking you’ll see a scheen in the water coming out of the tailpipes and your oil levels (tranny, ps, or engine) will drop.

You have a pic of this? There is no water in the oil?

what blocks do you have?

I believe

I've seen world blocks have casting/machining defects that caused this oil in the water before.