I have a 1990 Chris Craft 245 w/a OMC 460.
Backstory: When the out drive is in the proper running trim position, it overheats. If I trim down the temp returns to normal. I've replaced: all hoses. thermostat. cleaned all elbows. cleaned with rust remover all pieces. Replaced water pump in out drive. replaced water pump on block. Replaced spark plugs. Changed oil. etc. etc. etc. over the last 4 YEARS.

I do NOT want to discuss anything related to the engine over heating. There is nothing to fix. It's 600 hours and 27 years old.

That being said. I do not want to run trim down all the time as it sucks fuel and kills speed.

What I do want, is to replace the plastic 'intake grates' on the lower unit with grates that extend out between 1/4 and 1/2" from the side, thus forcing more water into the system when at speed.

I need a company/person that I can work with and pay to make them for me. It's a fairly simple concept. Take the existing grates, and extend them in a way that when the boat is moving forwards, sends more water to the pump.

Will this work? I don't know. If it pushes more water to the engine, it should cool the engine to the correct temp, as the thermostat will still limit the max amount of water.

If it doesn't work, I'm out some time and money.

I need this boat for another 2-3 years until I can buy something newer.

Does anyone know where in PA or how I could get something like this made out of metal or plastic? or ideas to test with before I have something made? Any ideas how to make a metal scoop at home? Some thin sheet of aluminum that I bolt in place?

I plan a test run without the grates to see if it makes a difference. Based on that I will either run with no grates for the remained of the boat's life. Or if no change, look to custom make a scoop type grate.

thank you!

for some reason I can't post attachments? Does that mean photos? ugh...
It's a King Kobra outdrive. I have photos, just can't seem to upload...

Those old KCs had a real ****ty water pump design, the impeller housing and the pump shaft and back plate need to be almost perfect condition or they will suck air and run hot. Also make sure you dont have a failing manifold that is putting exhaust pressure back in the cooling system , and making it hard for the water pump . Alot
of the old Cobra drives had that problem , with the water pump above the water line in the drive it has to have good suction , ( Mercruisers are below the water line so all they
have to do is push the water up). Also make sure that the leading edge of the sterndrive is free from big dents or gouges, and nothing is mounted to the transom infront of the drive ( Speedo tube , depth transducer ,etc) That will disturb the water infront and create turbulence.

^^^Your the only one not scared off by his warning.^^^^

Sounds like when you trim out, you are exposing the top holes in the water intake, and thus losing suction.

Can you try plugging the top couple of holes first and see what happens? Only problem then would be if you can keep enough flow.

I googled pics, it looks like most of them the water intake is cast into the drive...but if it's what I am thinking of, it would be pretty easy for somebody to fab some replacement plates with some minor scoops on the intake holes. Maybe even some plates with the holes in slightly lower positions.

Ayuh,.... My guess is, yer gonna starve the prop for water doin' what yer plannin',....

Any reason not to just use a transom mounted water pickup and a sea strainer?

Alot cleaner set-up and good water!
Then delete the water from the drive.

Jon

I was gonna suggest the same as cougar. BUT...you would need to add engine mounted raw water pump. But first, replace the impeller and housing in the drive pump. You need to do that impeller every year. Then try duct or Aluminum taping off 1 top intake hole at a time. Don't use silicon. It could come loose and suck in and block stuff and make everything worse.

Thank you guys (and gals. hard to tell from online names) Not a warning, just trying to keep it 'on topic'... I know we all want to fix the root cause of overheating, but at 600 hours and 27 years old... it is what it is.. I have a 12 year old Mazda that vibrates at idle. It has 175,000 on it. The fix... is a new engine? The $5.00 fix is raise the idle by 200 RPM... so... same thing here... an effective fix that will work for 2-3 years, and is under $400.00

I have a friend who has a machine shop, and ordered some 'new' grates on ebay. so we can mess with the current ones. Would I be able to upload photos?

I could try the duct tape thing. You may be correct that in the 'up' position it's sucking air. I don't think it needs a new impeller, as I've tried 3 last season, all with same effect.
No difference between one with 4 seasons on it, and one brand new.
If the outdrive trim is 'correct' for being on plane, the temp slowly, slowly climbs from dead center on the gauge to the red zone.
If I then trim it down a hair, the temp drops quickly back to dead center. You can almost drive the trim by the temp gauge. Amusing, but freaking annoying.

When in a position for keeping the engine temp happy, you can hear the excess drag on the hull/prop. Boat rides fine, but you can feel the drag sucking down fuel...

Anyone else wonder if ethanol in the fuel makes things run hotter as well? Hopefully the marina is ethanol free where we keep it now. Up until now I've had to use 10% at the pumps...

Not sure how the OMC transom assembly works, but is it possible that as you trim the hose coming through the transom assembly is collapsing or pinching off restricting flow once you pass a certain angle? Would explain why it cools right off after you drop trim down. I know that is sometimes an issue on Merc's.

that's a possibility, but I cannot find anything wrong with said hose assembly...