1991 king cobra overheating

[Blentine]

1991 four winns liberator with a 350 Chevy is overheating on plane ONLY due to air bubbles from the drive. I have dual side exit exhaust so it is not recirculating exhaust. I've replaced EVERY o-ring gasket and seal on the drive and am out of options.
I have also pressure tested it from the hose leading to the thermostat housing with no leaks. I have a clear hose from the oil cooler to the thermostat housing that is my obvious indicator that the issue is from the outdrive

I have fantastic flow through the block and risers,
I'm on my third impeller from burning them up, and am out of ideas at this point.
ive left three mechanics scratching their heads at my boat and can't find the issue.

**also when it begins to overheat within 20-30 seconds of being on plane, I can come off plane and rev in neutral to get good water flow through the motor again to cool it back down to operating temp


What could possibly be the issue??!!

 

[HT32BSX115]

1991 four winns liberator with a 350 Chevy is overheating on plane ONLY due to air bubbles from the drive.

Howdy,

Another LIb!!

It might help if you post the model number. 1990 and 1991 was 2 different drives Dog-clutch and the infamous interim cone clutch drive with the scarce raw water impeller (I think we have had this discussion)

If you're getting bubbles on a plane, are you also getting bubbles when you come back to idle or in neutral?

If that's the case, you have a leak somewhere in the raw water pump pickup or housing etc. The back of the drive is submerged for the most part when you're just sitting in the water.

When you get up out of the water (on a plane) the raw water pump is up above the water line........... and if there's a leak in the intake side of the pump above the waterline, it'll be sucking air (and aerating the water) ............At low power settings, the engine may not overheat but at high power settings aerated water may not transfer enough heat to keep from overheating above a certain RPM/power level.

You may have to look very closely at the raw water pump/housing and associated water pick-up area below it. I can't remember how my old dog-clutch Cobra plumbed the water from the pickup to the pump inlet but ANY small hole/leak would be ok until you raised it out of the water. then it would suck air.

Gotta love them Libs! I like mine!

Regards,


Rick