1987 Merc 350 5.7 Idle overheat and check ball adjustment.

[kaspern83]

Hello guys, I have recently replaced the impeller on my outdrive, rebuild the carb did full tune up.. She starts up great except after few mins or so on the muffs the temps start to go toward the 170 range. I also replaced the thermostat with the 142 degree one. From browsing around on the forum some people have mentioned that the check balls in the thermostat housing might not be doing their job.. Even with the engine at 170 the risers are cool to the touch. There is warm coming out through the hall and the prop.. I have purchased the GLM thermostat housing kit since mine was really rusted out and it came with new balls but I am not sure how to correctly adjust the screws in the end. Also is there something else I should be looking out for? I know for a fact that there is a freeze plug missing somewhere on the right side of the block (looking aft from inside the boat) But there is no water coming out anywhere. This boat has been sitting in dry storage for 3 years, should I be looking removing the exhaust manifolds and risers? They were replaced 4 years ago with GLM ones. Thank you for any help and advice.

 

[dubs283]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

the check balls now may be missing or stuck

just install the new ones and give it a try, if you need to adjust them do it, or the problem lies elsewhere

freeze plug missing?? - they aren't freeze plugs, they are welch plugs or casting plugs

are you sure its missing?? have you found the plug?? surprisied to hear that with one missing there isn't a leak, you will want to fully clean the hole and install a new one

best to learn why it came out too, when they come out due to not winterizing there is usually other issues as well

 

[tpenfield]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

If one of the casting plugs came out, there should be water all over the place. So, I suspect one of the following. . . Water is all over the place, or the new thermostat housing is not set up right and most of the water is going straight out the exhaust.

also, think about what causes casting plugs ( freeze plugs) to come out.

 

[kaspern83]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Sorry, the freeze plugs were out because the boat was winterized for 2 yrs in Connecticut. I just brought the boat down to Florida to enjoy year round boating =) I was not the one that winterized the boat but there were 4 plugs in a bag. I believe 2 plastic and 2 metal. My brother was able to locate the 2 on starboard side but the port side we can't find the location for the metal one. That's why we were going to run the engine to see where its pissing out of. Unfortunetly its not pissing out at all.

With the check balls I did get new ones. But should they be tight in there or pretty loose? There is a nut at the end to adjust... thanks in advance.

 

[tazrig]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Snug enough to hold them in place without falling out of the holes but not too tight. They need to be able to pull away (open up) at both ends to let water out when the system calls for it.

 

[kaspern83]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Thanks for fast reply. Yea the current checballs don't seem snug at all. Do you think it's a cause for my Ovearheating problem? What causes them to open up?

 

[tazrig]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Believe its when the thermostat opens up and re-routs additional water to the motor. They are there to insure the water only flows in one direction. If they were too tight and didn't open that could cause an overheat situation. But I don't think the other way if they were too loose would do it.

 

[Don S]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Those check balls do not seal in the thermostat housing. All they do is reduce the inside size of the hose so that all the water is not sent out the manifolds and risers.
There is no adjustment. Put it all together, tighten the lock nut so 2 or 3 threads of the long screw show and your done.

Merc stopped using the check ball, and went to a thermostat housing with a small hole to limit the flow to the exhaust, and didn't need the check balls.
Having the wrong hoses would be a problem, as they could allow too much water around the check balls.

 

[kaspern83]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Merc stopped using the check ball, and went to a thermostat housing with a small hole to limit the flow to the exhaust, and didn't need the check balls.
Having the wrong hoses would be a problem, as they could allow too much water around the check balls.

The hoses are all the same Ive been using since Ive purchased the boat 6 yrs ago. Had no issues of overheat before.

Not using the checkballs is something I could do? Or is it for newer merc engines only?

 

[Don S]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

You can't just remove the check balls, you need a thermostat housing designed for no check balls.

I'm just saying there is no adjustment on the check balls, and they are probably not your problem.

What shape is the raw water pump itself in, not just the impeller. Did you replace the gaskets? Is the housing warped or anything? Are you sure your temp gauge is accurate? Get a temp gun and check right at the temp sender and see if it's reading right. The engine could be running at 140, and you see 170 on the gauge.

 

[kaspern83]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Yea the housing for the thermostat is in really bad shape. I just purchased this kit View attachment 185211 going to install it and run the engine tomorrow see what happens.

Might as well get temp sensor also and just replace it. I hate it when stuff like that sits for 2+ years..

 

[kaspern83]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Don - The raw water pump was replaced 3 yrs or so too.. I have not taken it apart and replace the gaskets.. Ill check all too..

 

[Don S]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Don - The raw water pump was replaced 3 yrs or so too.. I have not taken it apart and replace the gaskets.. Ill check all too..

Replace it and see if it still has an overheat problem. At 3 years it's overdue, if it's been setting for 2 years the vanes are probably bent over permanently on one side giving you only half the flow from the pump you should get.
Have you done any actual output tests on the raw water pump?

Might as well get temp sensor also and just replace it. I hate it when stuff like that sits for 2+ years..

Throwing money at the problem is not going to fix anything. How would you know if it was a bad sender or gauge without actually testing.

 

[buzzm19]

Re: 1987 Merc 350 5.7 Idle overheat and check ball adjustment.

Just a thought, I had an overheating problem on my both 260 mercs and was pulling my hair out, the motors would overheat on muffs because I didn't have enough water pressure from my hose. I put the drives in a cut down 55gal drum and the overheat problem was solved. Those outdrives suck more water than you think. Buz