Johnson 35 Overheat

Knimrod

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This is a 1983 Johnson 35 (J35ELCTS) that belongs to my 80 year old neighbor. I offered to help, thought I could fix it but I'm stumped now. Started out with engine not running reliably and shutting off. I discovered a bad water pump impeller and replaced it. Assuming it overheated, I checked compression and found the top cylinder to be 150, bottom was 100. I pulled the head and replaced blown head gasket. Inspected cylinders wall for cracks but didn't find any. Engine starts and runs pretty good now but wants to overheat. Water comes out exhaust fine but no water from pee hole. I can feel a little air from pee hole though when running. It seems as if the bottom of engine runs cool but top gets hot. An IR thermometer will indicate the bottom half of cylinder head at about 140* and the top will get to 200 before the alarm goes off. I pulled the plugs and check the compression again and got 150/150. I then tried some compressed air into the pee hole fitting and air bubbles come out from water pump inlet as expected.. However, since I still had the spark plugs out, I could also hear air escaping from a spark plug hole. If I turned the flywheel by hand, the escaping air would change between the two cylinders. If I turned the fly wheel so both pistons were half way in the cylinder, I couldn't hear or feel any air escaping from spark plug holes.

I'm thinking that there is a leak between the crankcase or exhaust and the water jacket?. Where to look for this leak? Any help would be sincerely appreciated.
 
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Daviet

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Re: Johnson 35 Overheat

Welcome to the forum.
When you had the head off did you check the head to make sure it isn't warped?
 

boobie

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Re: Johnson 35 Overheat

When you had the head off, did you check the water deflectors in the block for not being swelled up ??
 

Knimrod

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Re: Johnson 35 Overheat

Welcome to the forum.
When you had the head off did you check the head to make sure it isn't warped?

The head was a little bowl shaped by a few thousandths.. I took a stone to it and improved it a bit. Seem to have a good seal.. Compression is 150 in both cylinders now.
 

Knimrod

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Re: Johnson 35 Overheat

When you had the head off, did you check the water deflectors in the block for not being swelled up ??

Not sure how to check them them but they "looked" alright.. I didn't remove them or anything.
 

Knimrod

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Re: Johnson 35 Overheat

I pulled the exhaust covers off and may have found the culprit. The lower right bolt (corner) was completely out and laying in the cowling under the cables. It looks like maybe there was some leaking from the water jacket (near that bolt hole) into the exhaust manifold.. I'll get some new gaskets and try it again. (fingers crossed)
 

Knimrod

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Re: Johnson 35 Overheat

No joy with replacing exhaust gaskets... When I put air in the water pee hole, it comes out either spark plug hole depending on where pistons are... Maybe this is normal? Since the exhaust is normally wet in operation, there must be a connection somewhere?

What else would keep water from the top of the engine (and the weep hole)?
 

Bosunsmate

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Re: Johnson 35 Overheat

Did you check your exhaust plates for warpage?
Have you removed the water jacket cover and checked the thermostat and channels for blockages?
 

Knimrod

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Re: Johnson 35 Overheat

Did you check your exhaust plates for warpage?
Have you removed the water jacket cover and checked the thermostat and channels for blockages?

Exhaust plate was pretty flat. I didn't remove the water jacket cover on cylinder head.. I guess that's next.
 

Knimrod

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Re: Johnson 35 Overheat

I pulled the water cover off the cylinder head.. No smoking gun there. The seal around the thermostat was wadded up on the side and probably not sealing good but I don;t think that it's causing my problem..

I did find something interesting in the exhaust cover yesterday though.. At the time, I thought it was a piece of wire but after looking at it close, it's a long skinny spring. At first, I couldn't figure out what it was for but it occurs to me now that it's a spring from a shaft seal. I'm not sure how it could have wound up in the engine if it's not from the engine but there it is and I'm not really sure where it's from.

spring.jpg

Any ideas on what seal and if it could be the cause of my overheat problem?
 

Bosunsmate

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Re: Johnson 35 Overheat

It could be upper or lower seal or gear box seal.
Id drop the LU and connect a hose to the inlet tube and see where the water comes out
 

Knimrod

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Re: Johnson 35 Overheat

It could be upper or lower seal or gear box seal.
Id drop the LU and connect a hose to the inlet tube and see where the water comes out

Thanks. I assume you mean the inlet tube that runs into the power head from the water pump? Pump water into the head and see where it comes out in the motor?

I also should have pointed out that the spring was in the water jacket, not the exhaust manifold.
 

Knimrod

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Re: Johnson 35 Overheat

Well, I haven't got the water hooked up yet but I removed the lower unit again and discovered the source of the spring. It appears to be the shaft seal assembly in the lower unit that's just under the water pump. Both seals were trashed and one had a missing spring.. This probably isn't the cause of the overheat problem but I'm now questioning if I had the water tube in the right hole in the upper unit. I will replace the seals and try again.
 

Knimrod

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Re: Johnson 35 Overheat

Seals replaced, careful placement of water tube and have water flow now and engine runs cool (about 140*)! However, the water doesn't start spraying from peehole until I rev engine up for a few seconds, then it's good and spraying at idle. Is that normal?

Next problem I'll probably start a new thread but in a nutshell, engine will die after a few minutes of running and the primer bulb will be soft. If I prime it hard again all is well for a few more minutes until it goes soft again. I found some leaky hose connections and replaced cable ties on hose with hose clamps but it didn't help. I pulled the fuel pump and the diaphragm is not torn or leaking that I can tell but it does look a little stretched out. Any thoughts? Thanx.
 

Bosunsmate

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Re: Johnson 35 Overheat

Yes that peehole spraying time isnt a problem, so long as it keep peeing. Careful reving a cold motor, reving a cold motor is one of the main reaosns i have never lent out my car as of yet.

Your fuel problem sounds like the valve in your primer bulb has gone
 

Knimrod

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Re: Johnson 35 Overheat

I sent the motor back to the owner. I think it's fixed. I'm thinking the problem with the water pump priming is because the water level in the tub I'm using does not come all the way to up to the water pump. I think in the lake, the water level will be above the pump and priming should be no problem.

I also temporarily installed a section of clear tubing in the fuel supply line just before the pump and I could see air forming in the tube when engine was running before it wanted to stall. I'm assuming an air leak somewhere in the tank, bulb or fuel line and told the owner he needed to find and fix that himself.

Thanks for the help!!!
 
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