1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

[rsein]

I have my powerhead off as I was trying to find whether my waterkackets or watertube were damaged, blocked. Engire runs extremely hot, scalding hot tell-tale stream (with steam) way too hot to touch.could make tea out of tell-tale water!
Block can't be touched. Changed entire water pump-still hot!! Pulled powerhead, checked water jackets, water tube can't find any obstruction. Don't know what to do next...is there any need to check crankcase gasket? What am I missing? Use to run fine but now I am afraid tio run it at all. Please help as I am at a loss!

Rod

 

[Korbs67]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

Shot in the dark from a rookie here but you may be on your way to detonating a cylinder if you dont figure out the cause then you have real problems. Timing could be off..have you touched the timing? You may have a lean fuel condition not providing proper lubrication to cylinders...possible causes are maybe a carb blockage or an autoblend issue not mixing oil/fuel. I have an '89 60 3cyl and these were my issues. Timing and carburation. Also, when you are done running the motor let it idle and cool with circulation while you go get the trailer. If you cut the motor and take out of the water there is nothing colling the motor at that point. Anyway. Let us know what the casue is when you figure it out..

 

[oldman570]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

You might want to check the water jacket plate on the exhaust ports and see if the divider plate is cracked and letting exhaust flow into the water jacket area of the motor. The plate will crack if the pump impeller has ever gone bad and the motor was still run. JMO
Oldman570

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

You might want to check the water jacket plate on the exhaust ports and see if the divider plate is cracked and letting exhaust flow into the water jacket area of the motor. The plate will crack if the pump impeller has ever gone bad and the motor was still run. JMO
Oldman570

Thanks oldman570. I'll have another look to see if the exhaust divider plate is cracked.

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

Shot in the dark from a rookie here but you may be on your way to detonating a cylinder if Timing could be off..have you touched the timing? You may have a lean fuel condition not providing proper lubrication to cylinders...possible causes are maybe a carb blockage or an autoblend issue not mixing oil/fuel. Timing and carburation. Also, when you are done running the motor let it idle and cool with circulation while you go get the trailer. If you cut the motor and take out of the water there is nothing colling the motor at that point. ..

Thanks for respondingKorbs67. I haven't done anything with the timing. I might be getting over my head if I start ripping this thing apart any further! I'll take off the carbs and have a look at those. The only way I use to be able to start this motor was by emptying half a can of quik-start into the carbs...maybe I damaged something by doing that? However this year, for some strange reason, it started up easily when tank tested with no quik-start. The waterjacket gasket around the plugs looked baked when I removed it...the exhaust port gaskets looked ok. I'll keep digging. Trying to avoid taking crankcase apart but may have to to inspect pistons and cylinders?

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

An update on my overheating issue. I have delved a bit deeper, The water tube inlet housing that goes to the powerhead appears damaged. I have ordered a new one with the seals (it's a discontinued part but I tracked one down on the net). I hope this is my problem. When it gets in and I get the thing running I'll post again. Also, the exhaust manifold plates looked good. The gasket was torn but not sure if this occurred when I took them off or not. I have all new gaskets so hopefully when all back together it will cool properly!

 

[redjmp]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

With the lower unit off, try shooting water up the copper pipe with a garden hose.
It should shoot out the telltale.
If not you have blockage somewhere.
Try running a piece of wire up the telltale hole followed by a blast of compressed air.
Make sure when you reinstall lower unit that the pipe and water pump re aligned.

 

[Korbs67]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

Good advice you are getting. As long as the lower unit is off its a good idea to slide a new impeller on and make sure your pump housing isnt melted. This happened to mine because I neglected it. It impeads water flow or can break off and get up into your powerhead water ways. Youtube has some decent how to videos. Very easy once youve done it. Odd are you'll need to replace it anyway if you havent for a few years. Also, prepare by having the pump gasket kit on the ready in case you tear it when you inspect. Its cheap insurance to replace anyway.

Visibly look through the saprk plug holes and look for signs of detionation..an overly dry cylinder or piston head or anything that looks obviously different from the other woul
d be suspicious. IF you have a crack in the exhaust manifold it will steam the cylinder and you will run hot then detonate which requires a teardown. This is the plate Oldman70 is referring to. Water flows on the other side of it.

Torque your bolts in the correct pattern in stages to reach your final correct torque value. Tighter isnt better, go to spec.

Before shooting air or water up the copper pipe might remove it first to clear any possible impeller chips, worn gasket material, etc. last thing you want to do is lodge something in the waterways of the power head by forcing it up there.

Have you checked your compression? Just curious.

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

Thanks everyone for the advise. Appreciate it!

Here is what I have done so far.
1-First I changed the impeller-still hot
2-changed everything in water pump cuz it looked scored-still hot
3-removed exhaust manifold plates, water jacket plate around spark plugs and looked for blockages-none found
4-checked where water tube enters powerhead-housing looked damaged-ordered new one

Have not checked compression or removed crankcase to access pistons. I will check compression next while I wait for watertube inlet housing to come in,

Is it possible there is a blockage I have not found in some other location?

Original impeller was damaged but no missing fins. I thought maybe there was caked on mud blocking water passages but everything looks clean.

 

[Grub54891]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

Does it have a thermostat?

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

No thermostat on this one.

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

anyone no where I can find the discontinued water tube housing part#79799? Mine looks bad but it is no longer available

 

[Korbs67]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

serial number?? did you check basics like compression yet?

 

[rsein]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

Haven't checked compression but will do that when I get it back together.

 

[oldman570]

Re: 1989 40 HP Merc 4 cylinder-powerhead-scalding hot!

It is hard to belive that there is no thermostat on the motor, unless someone has removed it. Most all motors of that vintage, that i have seen, have one. What is the SR# of the motor?