4.3 overheat

[donnymac]

I have a fuel injected 4.3, 2006. I believe it's called a semi-closed cooling system. Fresh water in the block, raw water cooled? Anyway, I have to idle out of the marina for about 5 minutes. Yesterday as I was clearing the marina the overheat alarm went off. I was still only idling so I shut It off and pondered for about 10 minutes. Fired it back up. started idling back towards the marina, overheat alarm again. Shut it down. Soo I pondered for another 20 minutes, started idling back towards the marina, The needle started it's climb back towards 190deg thought for a second then decided I'd boot it for the last 300 yards. Well 200 yards later the needle is dropping quick and stops at 160(normal is 175) So I'm back at idle putting though the marina and the needle slowly creeps back to 175. So I'm thinking, geez lets go for a boat ride. For 2 hours and all rpm's the problem doesn't return. Next day exact same scenario. Guesses? I knows?

Thanks
Don

 

[Don S]

Re: 4.3 overheat

You should have a flushing hose on the starboard side of the engine with a blue cap on it. Make sure it's tightened down 1/4 turn past hand tight.

 

[95yj]

Re: 4.3 overheat

If you check Don's suggestion and that's not the problem, then it could be your raw water impeller. On a 2006, your impeller should probably not need to be replaced yet, but overheating at low R's and cooling OK at higher R's could be the impeller. It's not pushing enough water to cool the motor at lower speeds, but when you pick up the revs, there's adequate flow to cool the motor or heat exchanger.

 

[donnymac]

Re: 4.3 overheat

Can I take the blue cap off while the engine is running(or just loosen it) and see if water is flowing? Once the engine has stopped overheating it won't overheat again. I cruised at 3000 rpm for a hour then idled for 1/2 hour no overheat. Until the next day. Then it'll overheat for abit then back to normal for the rest of the day.