over heat problem

[jwilkey84]

I just put a rebuilt lower unit on my johnson 50 hp, 1983 model. I took it to the water, but could not get the cables adjusted right, so I cant get it into reverse, it just wants to grind. So I went out on the water with just forward gear to try it out. I ran it a couple miles, it had a good stream of water coming out the tell tale, and then the overheat alarm went off. I was able to let it cool down and then idle back to the dock. I cant figure out why it overheated if it had good water stream

 

[ezeke]

Re: over heat problem

The tell-tale lets you know that the waterpump is functional, but tells you nothing about the circulation of cooling water through the actual engine.

The systems depend on properly functioning thermostats to open and close as needed, keeping the water circulating through the water passages.

Water that is not moving through the cooling passages bypasses but continues to flow.

 

[Joe Reeves]

Re: over heat problem

As Zeke suggests, your problem indicates that the water pump is weak and starting to fail. Replace the complete water pump and thermostat assembly.

 

[tashasdaddy]

Re: over heat problem

agreed.

 

[ezeke]

Re: over heat problem

Your shift rod has to be adjusted to a specific length, measured from the mating surface of the gearcase to the center of the hole at the top, slanted part of the shift rod.

The standard gearcase measurement for 1982 was 15-29/32" +/- 1/32" with the gearcase in neutral. I believe it to be the same in 1983.

After adjustment the slanted part should lean towards the driveshaft and be raised to engage forward gear before reattaching the gearcase to the midsection.

 

[jwilkey84]

Re: over heat problem

Well the lower unit that I just bought (the rebuilt one) is from a 1986, and mine is a 1983. I just figured that if they had the same # of splines, they would work.
I just replaced the tstat on the motor this winter, it probably has like 15 hours on it, could it be bad again? I did fail to check the impeller on the rebuilt lower unit before I installed it, but the guy said it was 2 years old so I figured it was good. I always had a stream coming out of the tell tale, would this indicate a good impeller?
I guess I will take off the lower unit again and check the impeller, if its bad, I have a new one. But if the tstat is bad again, I'll be irritated. That was quite a job just getting to it on the 1983 model where it is at the bottom of the motor. Talk about no room for wrenches! I have a '72 that has the tstat at the top side, why did they ever put them where you cant get to them?

 

[jwilkey84]

Re: over heat problem

Just a couple minutes ago, I replaced the two year old impeller with a brand new one, though the old one looked fine. The only other thing I saw in there was the metal plate that the impeller rides on had a little groove worn into it, so I also replaced that with one I had lying around that was good. Now I just need to make sure that the shift rod is in the correct position and reinstall it.
If it over heats again, what do I do? I have heard about the wax temp testers, can I get those at the parts store? Also, the heat alarm goes off before any damage is done, correct, if it was shut off immediately? When I shut off the motor I took a handful of water from the lake and splattered it onto the motor and it DID NOT sizzle, so should I be ok?

 

[ezeke]

Re: over heat problem

Whenever the engine is running, you should be able to put your fingers on the cylinder head for a full three count without undue discomfort.

When the horn sounds, you are over 200 degrees and some damage to the cylinder head and cylinder head gasket is always possible.

Good shop practice is to replace the cylinder head gasket. Minimal PM would be to re-torque the head bolts.

You can make a simple measuring tool for your shift rod with a pair of yardsticks and a crosspiece in an H shape.

 

[jwilkey84]

Re: over heat problem

Well I looked at the parts diagram for both years of motors and they share the same part number for the shift rod, so I would assume they are the same length.

 

[ezeke]

Re: over heat problem

sounds good

 

[jwilkey84]

Re: over heat problem

I just checked compression 5 minutes ago, and I still have 120psi in each cylinder. That's what it has been in the past, so that is a good sign too, right?

 

[ezeke]

Re: over heat problem

Yes it is.