Johnson overheating...head problem?

[will941s]

Helping a friend work on his Johnson 40hp, 2-stroke. Here is some background on the motor. It's a 1990 J40TLESR, serial # G2532019. Whats happened is it was having trouble starting, and the over heat alarm is going off. Also It's having some issues staying running. He replaced the T-stat, and replaced the entire water pump assembly. I went over today and performed a compression check. Last time it was done was about 2 years ago and it was at 130psi on both cylinders. Today it was 120psi on the top and about 98psi on the bottom. The plugs have clean oil on them and no appearant water mixed in. When the engine was running, I can hold my hand on the exhaust cover, but not on the head...it gets HOT. I took out the thermostat and smelled inside the hole, it smells like fresh oil/gas mix in the waterjacket and there is a coat of oil on the thermostat, and the old one had carbon built up on it. Is it safe to say he had a failed or failing head gasket? Or is there something else I should be looking into? Thanks in advance for any help.

 

[Big flop]

Re: Johnson overheating...head problem?

compression test looks a little off.
Blown head gasket will pump air into water passage.
Run with t stat out & t stat cover off and see if water comes out the hole?

 

[DJ]

Re: Johnson overheating...head problem?

Re-pull the lower unit. I suspect your buddy botched the water pump job. A simple task, if you pay attention, with lot's to go wrong-if you do not.

Now, you MAY need to replace a head gasket after such heat/cool cycles.

 

[will941s]

Re: Johnson overheating...head problem?

Thanks for the info. You know, I thought about running W/ the T-stat and cover off but was pressed for time at the moment....great idea and thanks for confirming. I will do that today. It smelled just like the the barrel of a prop after running the motor when I pulled the t-stat out, the oil and gas smell is something I usually don't smell when I remove a t-stat, esp. not carbon on the back of one. I did check the waterpump and it is correct, it pumps good....good flow out the idle relief port on the mid section and good stream out the pee hole. The rest of the motor is cool to the touch, including the exhaust plate...warm but I can hold my hand on it all day long. When I touched he head after about 1 1/2 minutes of running it was hot....to the point where I could'nt lay my hand on it. I removed the t-stat as soon as we shut it off and it was wide open (brand new), which I would believe if the head and water flow were functioning properly along with the t-stat the head would've been much cooler. He said the head gasket went out about 10 years ago, and the gasket had cracked right between the two cylinders, but it was so long ago he forgot the symptoms of it. If it is the head, is there anything else I should look for, or check out before I begin to pray and fight the bolts hoping they don't break? Anyone else had anything similar to this happen?

 

[paultjohnson]

Re: Johnson overheating...head problem?

:facepalm: There has gotta be a joke in there somewhere

 

[will941s]

Re: Johnson overheating...head problem?

DJ, little info on what you said. It ran hot about 2 weeks ago (alarm hot, not cut off hot). He took it out again and thats when it began having issues starting and at idle (again, ran alarm hot). When he replaced the waterpump, he said he blew a bunch of sand out the waterport where it goes to the base of the waterpump, and the rubber grommet that holds the water tube to the top of the water pump was corroded til it was almost closed, then it fell apart. Think a initial cooling issue on the first trip led to the head gasket failure on the second trip?

 

[will941s]

Re: Johnson overheating...head problem?

Paultjohnson......I own Mercs, work on small Merc Ob's that mainly have water jackets....not heads. Asking these questions to help confirm what I think, by experts who know these motors inside and out and may have more experience with issues and working on this brand than me. So therefore, there is no joke here....just checking if there is anything else I should be focusing on. Thanks for your time though.

 

[will941s]

Re: Johnson overheating...head problem?

Also, may say take it to a shop. We are both Law Enforcement Officers for the State of South Carolina, we don't make a whole lot of money and with gas at $3.60 a gallon, I learned to work on my own stuff, can't afford extra like taking it a shop....just like him.

 

[paultjohnson]

Re: Johnson overheating...head problem?

Paultjohnson......I own Mercs, work on small Merc Ob's that mainly have water jackets....not heads. Asking these questions to help confirm what I think, by experts who know these motors inside and out and may have more experience with issues and working on this brand than me. So therefore, there is no joke here....just checking if there is anything else I should be focusing on. Thanks for your time though.

I was just being a [ not so ] smart arse.... And really not refering to a motor at all... my bad... no offence........

 

[will941s]

Re: Johnson overheating...head problem?

none taken, just rather spend the money to do it right the first time. Learned my lesson on my old 77, Evinrude 70 that had a similar issue, replaced the head gasket to find out it was the exhaust plate gasket.....Hoping on this one it's just the head.

 

[paultjohnson]

Re: Johnson overheating...head problem?

none taken, just rather spend the money to do it right the first time. Learned my lesson on my old 77, Evinrude 70 that had a similar issue, replaced the head gasket to find out it was the exhaust plate gasket.....Hoping on this one it's just the head.

10/4 :facepalm: I will keep my fingers crossed for you that its a simple fix..

 

[will941s]

Re: Johnson overheating...head problem?

FIXED THE ISSUE. Took the head off and replaced the gasket, runs like a champ. Idle is perfect, no more overheating.....and the compression went back up to 140psi even on both cylinders. Way better than 120 and 98psi. The two compression rings on the gasket were cracked and the gasket material it's self was scorched. Funny thing happened though, I think I know why it happened. Before he took out a month ago, he ran it in the yard on muffs (the ones that let water in on both sides) and it began running hot...then the problems got worse. Anyway, after the gasket install, it begins to run hot again. I took the muffs off and used mine (cheap wally world muffs that let water in on one side), and it worked like a champ. SOOOOO, he took it out today and ran it and it was good. THE MUFF STYLE KILLED THE HEAD GASKET DUE TO OVERHEATING FROM LACK OF WATER PRESSURE.