Crusader 454 overheating

[madhatter66]

I'm throwing hands up and about to contact mechanic. Would like to see if anyone came across this problem and found the cause and solution.

1988 Crusader 454 with round 975hrs. This is on the meter even though ....
Top end was rebuilt 4yrs ago due to fiberglass fuel tank delamination

Starboard motor run great at 1500 rpms or under. Once at speed 3000-3200 rpms, she climbs and runs hot.

New
risers, elbows, swivels, thermostat, raw water pump-last year, coolant
switch from E35 water pump to the crank mounted water pump F6b-9
motor was ran with no cap on heat exchanger to release any air bubbles in coolant
when initially filled coolant level dropped so circulation pump is working.
coolant topped off while running to release air bubbles

Barnacle buster
heat exchanger and U-cooler.
U-cooler was continuous back flushed.
Heat exchanger was removed and placed in container and continuous pump flush of the buster.
Each raw water hose working from raw water pump to back was checked and good flow.
Good suction at thru hull to water pump. I have a clear cap water strainer.
Water strainer is about 6in above the water line.

Timing was noticed at 2 degrees before TDC. It was adjusted to 10 degrees before TDC.
To my untrained ears, at 12 I heard a slight knock when rpms were raised.
Again untrained ears. So she's set at 10 degrees.

I think I covered everything

[madhatter66]

Additional info

Raw water pump impeller was replaced even though I thought it could of been the problem.

Thermostat new is 160 degrees

[dsharp]

There’s not much more than you can do to it. I quit working on those engines for a living in the mid 80’s so I’m not 100% sure on the heat exchanger. Does it have the bolt on end plates? Did you check for old impeller blades in the bundle? Other than that, you might pull the circulating pump and take the back off and see if the metal impeller is ok. Some had a cast iron impeller and I’ve seen sheet metal impellers that had come apart. Can you keep your hand on the elbow when it’s running under a load? I still have a Seacraft with the crank mounted pump and it pushes enough water to keep it at 180 so it shouldn’t be the pump. Any chance of barnacles it the pick-up through hull? Start at the beginning and go to the end. You have to be methodical sometimes.

[rmatt]

Are the hoses old? I have seen hoses that deteriorate and cause a kind of flap to come loose
partially blocking flow. Also as mentioned impeller blades in the heat exchanger there can be broken
zincs there too. Is it really over heating or is your gauge lying to you?

[miboatnutz]

Might not be the cooling system problem at all. You could have a carburetion issue where the mixture is leaning out under load or a timing issue where you're not getting enough advance at higher RPM.

[Finalee]

Check the trans cooler. Remove and flush. Often overlooked.

[madhatter66]

Hoses are only 4yrs old. No blades due to new raw water pump (1yr old) and i replaced thinking it was the cause. Installed new impeller cause it was a pain to remove old one. It was still nice and snug.

[madhatter66]

The timing was set to 10 degrees before TDC. Didnt think of carb. I'll mention to mechanic.

[madhatter66]

U cooler does both oil and trans. It was back flushed with barnacle buster. So did not remove. The heat exchanger was removed and flushed.

[MadHatter53]

Usually high speed over heating is from a lack of flow. Your obviously FWC so did you do the 50/50 mix of coolant. Could be a fuel issue as noted before, if it was a head issue you would have a loss of coolant and other issues. Check the flow out of each exhaust at idle and above,you say hot but what are the temps? Any steam from the exhaust?