Think outside the box here as almost everything has been changed. My 4.3 Mercruiser V6 I/O overheats once it goes above 2,800 rpm and only under load. It doesn't overheat at the dock or under 2,500 rpms. Once I start to over heat and I bring the boat to neutral it cools down in 30 to 45 seconds. I'm not a mechanic so some of my parts or terms may be off but so far and close to this order:
1. New water pump
2. New Thermostat
3. The block is not cracked
4. Risers and exhaust are good (floppers checked also)
5. Hoses are new
6. Removed the closed fresh water cooling system (now cools off salt water)
7. Changed all gaskets
8. New water distribution housing
9. New Thermostat housing
Also the sensors are good as the engine was checked with a heat gun. The timing is correct and no growth or blockage on the outdrive. Any idea what else...
4.3 Mercruiser V6 I/O- Cooling help
2,400 views·12 replies·by Bassknuckles
The engine had a half closed cooling system on it so the engine block was cooled by anti-freeze and not salt water. It was removed thinking that it was the problem.
MateOriginal Crew210 postsSince 2019
Yea that was changed also. I'm guessing their is a blockage somewhere. Thanks.
MateOriginal Crew210 postsSince 2019
It's been a problem the last two seasons. It may run warm for 1 or 2 trips then have issues and run hot. I believe their is a flow issue somewhere. Next trip I'm going to take the heat gun and measure the temp in certain areas of the engine to see if it's only on one side or certain area on the engine
MateOriginal Crew210 postsSince 2019
Risers were checked last year. New elbows this year
MateOriginal Crew210 postsSince 2019
Does it still use the engine circulator pump in addition to the raw water pump? Has that been looked at?I don't know, I will add it to my list for the mechanic
MateOriginal Crew210 postsSince 2019
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