Merc 4.3l overheating troubleshoot order

What would the logical, typical troubleshoot order for working a overheat issue in this engine?

2006 MERC 4.3L TKS 190HP MOD: 4211025TT SERIAL: OW614342 - RAW WATER COOLING SYSTEM

The engine began to overheat (on muffs) the first time it was cranked up after sitting idle for roughly a year. I took boat to a marine shop, and the water pump/impeller was replaced. The mechanic said the impeller was in "good condition", but it was a good idea to replace it anyway. When I got home, the engine was ran with muffs and began heating up again, it was shut off immediately after alarm went off. I'll be taking a look at the thermostat next. Any other suggestions?

Re: Merc 4.3l overheating troubleshoot order

Are you in salt or fresh water?

On muffs, start the engine and remove the inlet hose to the thermostat housing and see if you have a good flow of water from the drive.

Re: Merc 4.3l overheating troubleshoot order

OK, I removed the thermostat and it was in pretty bad shape, dirty and stucked. I already ordered a new t-stat kit. I also found several small impeller chunks inside the thermostat housing and engine block. All 6 attaching hoses were clean and debris-free. I cleaned the housing pretty good, but not sure the correct procedure to backflush the engine block in order to remove all the impeller debris inside. Can someone explain the steps to accomplish this?

2006 MERC 4.3L TKS 190HP MOD: 4211025TT SERIAL: OW614342 - RAW WATER COOLING SYSTEM

Don; the engine has operated both in salt and fresh water, possibly on a 50/50 basis. After use, it has been muffs-flushed every time.

Re: Merc 4.3l overheating troubleshoot order

FLANDY said:

.... I also found several small impeller chunks inside the thermostat housing and engine block. ....

Click to expand...

That's a Gen II drive, which means for the water pump impeller to have disintegrated it's been run without water for a considerable amount of time... You will need to remove and clean out the power steering oil cooler, the water check valve ,the manifolds and elbows... You also need to drop the lower gear housing and replace the dead water pump impeller. I would suggest that the housing and base plate are going to need replacing too....

Chris...........

Re: Merc 4.3l overheating troubleshoot order

Chris, I appreciate your input, and definitely will take a close look into those components. Actually, the water pump was just repaired, and that impeller debris found inside the engine block and t-stat housing must be from a previous break down. What leaves me with my original question unaswered; how do I back flush the engine block?

Andy.

Re: Merc 4.3l overheating troubleshoot order

Remove the thermostat. remove and plug one of the hoses going to one of the exhaust manifolds. Push water into the hose from the other manifold. Once you're happy that side is flushed, swap the plug and the water source over to their other sides.... That back flushes the engine... I would also pull the drive and check the water pocket cover (it's cast in on those drives, so you should flush that too, and the hoses and coolers from the engine to the bell housing....

Re: Merc 4.3l overheating troubleshoot order

Admiral, you rock! Kindly appreciate the info sir