Overheating issue! Nothing left to replace?

[Csand714]

Hey everyone, I’m new to the form and new to boats. I’ve done a lot of work on motorcycles and cars but this boat has me bearing myself up.

For starters I bought the 84 well craft for $500 as a project boat since I’ve been looking for a good project. I expected to put money into to this and that’s exactly what I’ve done.

To clarify, the motor is a gm 350 5.7 Mercruiser Sterndrive and it’s fully raw water cooled.

It has the SEI06 alpha one gen one replacement on it and a quadrajet carburetor.

Since buying I’ve done lots of work to her. Originally she didn’t run but now with lots of hard work and time I’ve got her start up and run until it dies from overheating. I can’t seem to beat this over heating issue. It seems I get the motor started right up on muffs and the temperature climbs up to 240 and dies. When trying to restart it’s very difficult to start and when it does it just backfires immediately and dies. I’m almost positive this is due to the ignition module heating up because almost everything else is new. As far as cooling components go, I’ve replaced the water impeller pump and housing, entire exhaust manifolds and elbows, and thermostat (140 degree). My circulator pump doesn’t seem to have any leaks or issues and the block seems to be clear of any blockages. Heads were recently resurfaced and serviced which led to new head gaskets and intake manifold gaskets. I’m about to drop it in the water to see if the muffs are the problem. Other than that I’m really at a loss here. Please any suggestions are welcome!

Here’s a pic of my cooling diagram.

 

[Fun Times]

One thought would be if you haven't checked or replaced the water pocket cover yet then maybe you have an issue with the upper drive shaft housing water pocket cover as that area could be warped causing air ingestion or a melted down blockage impeding water flow even if you see "some" water flowing out the exhaust system.

The pocket cover and related parts & gasket area item numbers 2 - 6 in the following link for you to see, https://www.mercruiserparts.com/bam/subassembly/30870/2203/80

You'll have to remove the lower gear housing and first look up high in the drive shaft housing to see if you see anything obvious but the gasket and cover housing could be warped and you may not see it until you remove the cover.... But try to be careful as the screws (#5) could break off easily up there.

Temporarily installing a clear water hose to the inlet side may help you indicate if there are any air bubbles coming from the outside of the boats cooling system.

 

[alldodge]

muffs and the temperature climbs up to 240 and dies

Don't let it run long enough to get to 240, you can blow the head gasket and warp the head

Agree with FT, look to see how much water is moving.

Also are the check balls in the thermostat housing? If check balls are not there, it can reduce the amount of water going to the motor

 

[Csand714]

It appears the picture in the right of your attached picture, alldodge, is my exact cooling system (updated thermostat housing as well). As far as the check balls, they are there in the thermostat housing and not sticking. However, they are very loose meaning easy to pull, not sure if that matters. This is the first time I’m really understanding the term water pocket cover. I always thought that was referring to the impeller housing which confused me as I never had issues with any of those bolts. Thats going to be the first thing I check. I’ve checked for water flow numerous times by pulling hoses off at different sections to ensure water flow and it seems substantial. But I have also noticed water leaking out near the shift linkage on the outdrive but I always thought that was normal. That could very well be a leak at the water pocket, fingers crossed you guys are correct because this has been driving me insane. Thanks so much for you help Fun Times and alldodge!

 

[Csand714]

After running into some carb issues, I was finally able to run the engine long enough for the temp to rise. Unfortunately the overheat issue is still there even after changing out the water pocket cover. The old one did seem a little warped at the pickup tube connection end but nothing crazy. However, I replaced it with a new one anyways. I’ve back flushed the block multiple times and even unscrewed the drain screws on the side of the block to flush out some old crud and did so until the water was clear. I’ve ran water through almost everything and replaced almost everything. The only old parts are the water circulator and thermostat housing. I know it’s not the sensor or the gauge because I have used a infrared temp gun to double check. I think I’m going to drop it in the water tomorrow and see if the muffs are the problem since the engine seems to be designed to pull from an ocean or lake. Wish me luck!

 

[Mlevy]

I just went through the same issue with my boat, i have the exact same cooling setup as yours. I borrowed a thermal camera from work to watch the thermostat housing heat up. Turned out all the cool water was passing by the check balls and not moving through the motor, up through the thermostat and out the risers.

I took apart the balls and stretched the springs out. They need to be fairly snug to the outlet so there is some back pressure on the system. Keep stretching until the temps get to normal. It could also be not enough water on the muffs, best to put the boat in the water to rule out. Hope that helps!

Mitch

 

[alldodge]

Good luck :thumb: