What should my oil temp be in my HP500. Seems to run 150 - 190

That's pretty low. Takes 212* to burn moisture off. I'd say +,-220 would be ideal. Might be a good idea to pop a cap off the valve covers and check for milk shake.

Why would it run so cool?

Those are post-cooler temps and pre-cooler temps are probably in excess of 300*F. You have a great oil cooler and must be running in cool waters too?

What oil and viscosity are you running?

oil is 25 x 40 I guess the water temp where I am running is 70 degrees. This makes since as there is no "milkey" condition under the valve covers. Lookes brand new and clean in there.

HYDROCRUISER Can you tell us where the oil temp sender is located in an HP500EFI.? Mine seems to run about the same temp, which I thought was low, but I do not have any signs of moisture in the top of the motor. I just assumed the sender was somewhere in the oil pan, thanks for the info.

...just in front of the filter boss adjacent to the pan rail

..I think..

I think you are fine and 70*F water is a factor for your cooler temps. Start to worry when your needle says 300*F

If you want to see your oil temp go up just add about 8 lbs of boost...

The 502's were about the best "stock" engines out there...they don't break a sweat for the most part and can handle lots of upgrades...why GM said "no" is beyond me.

HYDROCRUISER Thanks for the reply, next time I have my boat home I will make it a point to find out exactly where mine is. Seems to me it would be much more realivant to know the highest temp, ie the pan or just before the cooler, not after the cooler. Wonder why Merc did that? Will post when I positively find mine.

Avoid installing Oil Temp Senders in engine block. Cast Iron acts as a terrific heat sink and will give you erroneous readings. Oil Pan bung (preferred) or Remote Oil Filter Mount (second best) will give you your hottest temps.

What are you running for an Oil Cooler?
(Stock HP500 oil cooler is 2" x 17")
Do you have the Mercury Racing T-Stat controlled Oil Filter Mount?