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Mercury 60hp 1985 model Overheating problem

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nickc

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"Hi, Just wondering if someone

"Hi, Just wondering if someone could please help me!
I have a 60hp mercury outboard 1985 model 3 cylinder which has been fully serviced including water pump kit, carby kit and tune, fuel pump etc. The motor is overheating but pumps lots of water. At 3/4 throttle the temp gauge will read 240 degrees F and the water coming out of the engine is very warm to hot. The motor has a new temp gauge and sender. I don't believe this model outboard has a thermostat. The motor runs very well just overheating. Is there anything else that could be causing the engine to run very hot? My local mechanic I take the boat to has no idea!

Thanks, Nick."
 
"Nick, assuming that the water

"Nick, assuming that the waterpump was assembled correctly and no seals/gaskets moved or slipped on you, I would check the following:

The water tube itself. I have seen them with holes (burned) right through them. Mostly in saltwater run motors, but the tubes are just metal (usually copper) and will (rot). I had one go on my 1991, freshwater run motor.

The seal where the watertube connects to the exhaust plate (top of the tube, bottom of the powerhead). This usually means pulling the powerhead, but that only costs the price of a base gasket and a bit of your time.

This motor should be a "headless" split block which means you can inspect the water jacket by removing the cover (spark plug end of things). Again, for the cost of a gasket you can get a good look at the water channels around the cylinders themself. Saltwater, hard water, polluted water etc can cause a severe mineral build-up in the water jackets restricting the flow.

That's the three areas I would concentrate on if you are satisfied the waterpump is doing it's job. But I really would check the waterpump seals and the seal where the water tube enters the pump before moving on to other troubleshooting. 99% of the time, that's where the cause of an overheat problem will be found..."
 
"Thanks for the info Graham! I

"Thanks for the info Graham! I took the boat to another mechanic for a second opinion. He check the water pump to see if it was assembled correctly, all was good. He also took the boat for a water test and wasn't to concerned that the temp gauge read 240 degrees F. I'm not sure if i have the knowledge to remove the powerhead to check for salt build up. Is it difficult for the average person to do?
Thanks Nick."
 
"To simply check for build-up

"To simply check for build-up in the water jackets, you do not need to remove the powerhead.

Back where the sparkplugs are, there is a cover (that basically is where the "head" would be if it had one) that can be removed.

You would simply take out the spark plugs and undo all the bolts around the perimeter. This is just a water jacket cover, but does have a gasket that would need to be replaced (and probably the old one would have to be scraped off).

With that removed you can see all you need to. Any salt build up can be removed with a solution of 50% white vinegar and 50% tap water. That works just as well as the commercial concoctions and costs about 2 bucks
Usually a 24 hour soak (I tilt up the motor, pour it in and let it sit), will disolve all the "cooties".

Then just reinstall the cover with a new gasket. There is no "engine pressure" here, so really don't have to worry about torque spec's etc. The most that cover is holding backs is the water pressure from the impeller (maybe 12 psi max). Normally, I would put about 10 foot pounds if I was using a torque wrench, which is basically finger tight plus about 1/4 turn with a normal wrench..."
 
"Thanks Graham, I removed the

"Thanks Graham, I removed the cover and checked inside the water jacket. Surprisingly it looked very clean I couldn't see any salt build up. The gasket looked as though it was new and come off easily so I reinstalled the old gasket. I started the engine to check for leaks it seemed OK. Should I check anything else? should the motor be cooling efficiently because there was no salt build up in the water jacket area? I have really appreciated your time and advice!
Thank You, Nick."
 
"Yes, the cooling system is su

"Yes, the cooling system is super simple. If the intake on the lower unit is clear of debris - the impeller is pumping water - the water tube is intact and the water jackets are clear, and the thermostat and poppet (if equipped) are functioning, that's all there is too it - just water in/water out..."
 
"Thanks Graham, it took the bo

"Thanks Graham, it took the boat out yesterday and the temp gauge still hit max at 3/4 throttle. I noticed that the top exhausts holes (not sure of the correct name) don't pump out a lot of water when the motor is going. I started the boat when I got home to flush out the engine, there is a rubber water tube that looks like it supplies water to the top exhaust. I disconnected the tube from one end while the engine was running, there was a good flow of water coming out of the tube and the flow from the top exhaust stop. I reconnected the tube and the flow from the top exhaust started again, but the flow of water was a lot stronger with the tube disconnected. The top exhaust holes only shoot out a light spray of water. Is it possible there might be a slight blockage somewhere that feed water to the top exhaust, what should i do if this might be the case? Thanks again for your help! Nick."
 
"Almost all the cooling water

"Almost all the cooling water does go down the exhaust. Serves two funtions - cools down the exhaust and forms a "wall of water" in the exhaust housing to act as a muffler.

Those top exhaust holes should only "spit" or "mist" as most of the water will exit the lower unit.

I'll have to dig in the manual at this point and see if there is anything else that is not coming to mind about the cooling on this particular model. The only other possible constriction to the water could be on the powerhead base itself.

The water tube feeds the water up to the base of the powerhead just behind the carb(s). From there it travels around a channel to the waterjacket itself (which you have already checked). It sounds like you have an auxilary hose to get water up to the top of the cylinder (my 140 OMC has a pair of them) but you note that the flow is good there (????).

When your temp gauge is going real high have you tried putting your hand on the powerhead itself? too hot to touch??

If it's not, I'm starting to wonder if you have a bad sensor (even though it's new)."
 
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