I have a 2003 Four Winns Funship deckboat powered by a 5.7 ltr Volvo Penta dualprop GXI. My first time in the water this year the boat temp. went up and hence took it back to the repair shop who previously PM'ed it. They told me that the coolant lines were blocked by milfoil weed which was rampant in the marina. They said that they blew out the lines and it was fine. The next time that I used the boat, it was fine. The time after that I took it out, it ran fine again. However on the way back, it heated up again. I made it back to the marina keeping the rpms under 1800 and it stayed cool. From then on I have not been able to run the boat over 1800 rpms without it heating up. To date, I have taken it back to the repair shop and, while I watched, checked the coolant lines which are clear, ran the boat at idle for a half hour in neutral at various high rpms without issue, checked the water flow, replaced the themostat, heat sensor and still in gear it heats up over 1800 rpms. What next?
It is possible you have an exhaust restriction. When you run the engine out of water does water run from stern in both outlets?
30 years professional marine mechanic=skilled in all phases of the marine service industry.
I just had it pulled out of the water at the service place this weekend and I don't think that they have looked at it yet. I don't have a lot of confidence in them diagnosing the problem. In fact, I did the thermostat myself after waiting for them for a week. I can fix mechanical but not technical problems myself. So I should put a boot on it and see if water runs out of both sides of the outlets......and if it doesn't, where should I start to trace from to check for a restriction?
What i was getting at was in the exhaust "Y" pipe are "flapper valves" that help to stop water flow into engine exhaust when backing down quickly off plane. Just maybe they have broken and fallen down the "Y" pipe and blocked off the water flow out . This will over heat the engine.
This overheat happens anytime that you are over 1800 rpms period. The other day while going headway speed, I dumped the throttle so as to allow it to plane off quickly to see if planed off vs plowing at 1800-2000 rpms made a difference and it didn't. After a minute or so the temp gauge still shot up.
Well, even so it still could be exhaust restriction. You can run that engine all day long at 1800 rpm with one side of exhaust blocked.
..........and with this possible restriction, it could still run in neutral for a long time at high rpms and not heat up at all??
No...We have to look elswhere. Can you run the engine out of the water?
Yes, I'll have to put the muffs on it but I can do it. What would you like me to do when I get it hooked up? It will be in neutral and hasn't heated up that way in the water.
I'm going to the marina where the boat is sitting drydocked. You mentioned to me to run it out of the water (above.) What do you want me to check??
I suspect an air leak into the water system from out side the boat. Possibly the hose connection to the drive. Or a restriction at the screen in the lower unit. First connect a water hose To the inlet hose from the drive. Check water flow. Look for leaks at drive connection,and good flow out bottom of the drive.