1986 140 Johnson Overheat and loss of power

[mercmafia]

I have a 86 140 Johnson on the back of a 21 foot Chris Craft Scorpion open bow outboard. I pulled the lower last season and replaced the impeller and the housing. Then the first time I took the boat out I was getting an overheat alarm. I removed the thermostats and found that one of them was melted so I removed both of them and put it in the water and still have an overheat. After reading on the forum, I decided to backflush the coolant ports on the head and now this time when I dropped the lower, I noticed that the gasket for the exhaust housing on the upper was ripped and twisted...would this cause an overheat scenario, where water is pushed away from the motor while trying to get up on plane?

And as the loss of power goes, the boat will not get up on plane without the overheat alarm going off. But if I let the motor cool, I can give it throttle and it acts like it is starving for fuel. And if it decides to get up on plane, the motor will deaccelerate very quickly and then sit there and either shut off or begin shaking violently and rev up and down repeataly. I have been told to check the check valve off of the fuel tank but I do not see one. All I see is a shut off valve mounted to the top.

 

[Bosunsmate]

Re: 1986 140 Johnson Overheat and loss of power

get someone to pump the fuel bulb to see if that fixes it, if so it may be running lean from a bad fuel pump.
Check the fuel bulb goes hard with engine off too.

 

[Solittle]

Re: 1986 140 Johnson Overheat and loss of power

I would check to see that the water tube from the water pump is properly seated into the block.

Have you checked the deflectors in the block? Either that or some other blockage in a water passage.

Forget checking check valves or other fuel things - your engine is acting strangely because it is overheating - period. If you keep trying to run it this way it will ultimately freeze and then you are looking at big $$$.

 

[V153]

Re: 1986 140 Johnson Overheat and loss of power

I would double check the water pump assy as well.

You say you removed the thermostats. That's a no no. My bet is you're pushing too much water through the block, faster than it can absorb the heat. You shouldn't just completely remove the thermostats. You still have to restrict the water flow.

Typically I don't run tstats in my V4 OMC motors, because I boat in very warm water. But I do restrict the flow. This can be done with a stainless fender washer, or simply by chopping the guts offa the old tstat.

I'd definitely invest in a pair of head gaskets. Pop the heads'n have a look see. The water deflectors are very important, ya might wanna invest in a set of them beforehand too. Cuz they don't like being overheated. They tend to shrink and/or deteriorate. Combine that with too much water pressure'n you've got a recipe for disaster.

 

[boobie]

Re: 1986 140 Johnson Overheat and loss of power

That motor doesn't have water deflectors in the block.

 

[V153]

Re: 1986 140 Johnson Overheat and loss of power

That motor doesn't have water deflectors in the block.

Huh? Since when? If'n it's a crossflow it damn well better. My '86 90 (same block) did?

 

[boobie]

Re: 1986 140 Johnson Overheat and loss of power

I do believe the '86 140 is a looper and they didn't have deflectors. Check it out.