well I found out yesterday that all this was for nothing. when the gauge shows 260 the oil pan temp is 180-190. the shop that put the motor in broke the original sending unit and replaced it with the wrong one. I should have started with the simple things first lol!!!

Don't wish to be repetitive, here are my three suggestions:

In the order of importance----
1) dump that wimpy oil cooler and install the largest, non-chrome cooler that you can find.
Reason: 600 + ci w/wet sump oiling

2) disconnect the outdrive water pick-up point at the inner transom plate. Install a thru transom water pick-up
Reason: com'on, 700-800 hp and your still using the Merc water pick-up system?????????? Can you say restrictive!!!!

3) remove the crossover and install a water recir pump w/ a t-stat and water by-pass hose.
Reason: Puts your motor in control of the water flow and temp thru the motor. Hey, look at Merc racing motors and see what they use.

#1 and 2 are a must. #3 is optional.

FYI: The Keith Eickert oil thermo unit has the internal valve "open" for oil cooling set at 215-218 degree's.

thanks but its fixed. It was the oil temp sending unit. I had the same setup with my 622 ci motor and it never let me down.