help, why is it overheating?

[Coontakinta]

I have a problem that I’m hoping the likes of Noelm and others can help with. My 1996 25hp Johno HJ25RAEDA has been a loyal servant for many years. Almost 13 infact.
That’s was until the middle of last year until a long lay up for many reasons saw the need to be towed in from a planned trip for what later was found to be a seized thermostat.

Anyhow I digress. The old girl had been performing admirably since until the last week or so when I had noticed once again that the exhaust water was steaming and the leg was getting very hot. The tell tale water is warm and occasionally disappears along with the water from the exhaust.

As a result, I pulled off the lower unit and checked the impeller even though it and the pump assembly were replaced around 18mths ago. All good there. Next was to check that the thermostat was ok. So removed that and tested in a cup of boiling water. No worries opens up freely. So only thing left for me to check was that the cooling galleries went blocked. I did this with compressed air putting the gun in any orifice I could where the water could normally flow, the water intake in the lower unit, the thermostat orifice, and even back up through the tell tale pipe. Air is coming out of all those areas when I put the compressed air in what I think is good volumes.

So my question to you all is WHAT NEXT? I’m stumped. I’m thinking I might run the unit without the thermostat for a period and see what happens to the water flow and temp that way. Will there be any long term ill effects by doing this. By run I mean test at home, NOT run over a prolonged period so I can use the thing.

Is there another way of checking / clearing any blocked or restricted galleries.

Can anyone advise me on what the problem might be and how to fix it.

Thanks

[trev1]

If it has been really hot, sometimes the heads will start to leak at the gasket. Simply retorquing the head sometimes will do the trick but usually you will need to pull the head and the cover gasket, clean everything up , and re-assemble. This has its hidden horrors too ,in the form of broken bolts,ect, especially on a motor that old.

[tunaticer]

My 95 Evinrude has been steaming a fair bit of late after a run to get it warm. The powerhead feels well cooled and definitely not too hot to touch or hold.

I am thinking maybe there could be some corrosion in the exhaust route somewhere before where they should be meeting letting hot gases steam up the already warm waters. Unknown for me too as I have checked everythign for blockages and the waterpump is entirely new and the seals and seats for the pickup tube are good. Compression on mine is within 4psi pot to pot at 124-128psi.

Until it starts to die off from heating im not taking it any further. So far it hasnt lost any power through being hot.

Jack.

[Kleyny]

My suggestion would be to use water in the water jackets not compressed air.
IMO compressed air might go through a blockage whilst water being a little thicker may get stuck.

I had a tell tale flow issue. When spoke to an outboard mechanic and he suggested to remove the thermostat and leg, the jam the garden hose in the thermostat hole and turn the water on. Water and anything else thats in the water galleries would then come out of the leg tube.

Simple yet effective.

Did this work for me NAH i had a little shell in the tell tail tube that would move out of the way when you poked a wire up there.

i would also replace the impeller so at least you known its right. Their only cheap mine only cost 50 clams.

neil

[Spaniard_King]

Most likely you have warped the cylinder head from the previous overheating.. this is common with these 2 cyl johno/Evinrudes.

Remove cylinder head (I bet you find it warped) if warpage isnt too bad get it machined flat again. clean out water galleries in vaciniuty of the cylinders and re-install head with new gasket.

[DAVE_S]

I would say that the power head needs to come off, and you will find the rubber grommet on the end of the pick up tube that connects the water pump to the power head has melted and restricting the water flow .
I thing they call it ducks disease .

[ryank]

hey mate. ya impeller might look decent but it may have lost its tension exspecially from sitting around.

[ryank]

hey mate. ya impeller might look decent but it may have lost its tension exspecially from sitting around.

[Splash]

mmmmmmmm sounds very familar....... :)

In addition to all said above - remove head and replace all the rubber tubular (licorice type shape) inserts that lie in middle between top and bottom cylinder external walls (about 4 all up). When these tubes deform with age, they stay deformed and swell which then heavily restricts water flow and can block water flow around all the cylinder head wall jacket.

I would also retain the the t/stats.

Do a search under username 'Smelly' circa Dec 2006 and July 2007. Look for 'Overheating' and will find all your answers :) 8-)

Good luck!

Splash

[Coontakinta]

Thanks guys some helpful ideas there and the cylinder head theory sounds very plausible. Infact doesnt a car with similar issues suffer from similar symptoms ?????

I'm not much of a tech wiz with these things. Is there anything I need to be aware of in removing the head, other than the previously mentioned bolts ??? Springs or similar that might wanna pop out? If the head is warped can anyone give me an idea of cost to ahve it machined and where I might be able to have it done? (am in Adelaide so generalisation / type of places rather than specific please)

Or should I just take to a professional form here?

Thanks for your assistance to this point guys, would appreciate your continued support.

Cheers

[Splash]

firstly, disconnect your battery.

after head is removed, lighty cover inside of cylinder walls with 2st oil and cover powerhead with towel to keep insects, moisture and shit out.

ensure you have your manual beside you.

put bolts in safe orderly place.

read the 'smelly' posts referred to earlier..

Splash

[Splash]

Most likely you have warped the cylinder head from the previous overheating.. this is common with these 2 cyl johno/Evinrudes.

Remove cylinder head (I bet you find it warped) if warpage isnt too bad get it machined flat again. clean out water galleries in vaciniuty of the cylinders and re-install head with new gasket.


SK - when is a head beyond repair (how much warpage is repairable)?

Splash

[Spaniard_King]

SK - when is a head beyond repair (how much warpage is repairable)?

Splash

Splash

0.010" is repairable (checked with straight edge and feeler gauge)

Coota.. anyone with a metal lathe should be able to do it. A mill would also do the job as its only a 2cyl head.

The Head is easy.. its all infront of you (ie undo things as you see them in front of you)

[FNQCairns]

Before you get the spanners out, check the head with your hand, everything you have mentioned can conceivably fit normal operating conditions. My identical engine behaved the near the same as yours.

A compression check wouldn't go astray either but for certain check the temperature at the engine before all else.

cheers fnq

[Splash]

Splash

0.010" is repairable (checked with straight edge and feeler gauge)

Coota.. anyone with a metal lathe should be able to do it. A mill would also do the job as its only a 2cyl head.

The Head is easy.. its all infront of you (ie undo things as you see them in front of you)


thanks sk - i wish i had of checked my heads when they were off last year..:-[

Splash

[Coontakinta]

Well a BIG thanks so all for there help.

Before attacking the heads was alerted to an old aquaintance to the family that used to head the service dept of an ex OMC dealer here in Adelaide. After discussing the predicament to him, he went off to gather some info for me.

Yesterday he gave me the good (perhaps bad news). "Dont think you have a problem mate! The temp of the water shouldnt exceed 180oF approx (80oC) so long as you have that u have nothing to worry about" He went on to explain that there wont always be water from that port until such time as the thermostat opens, which I realised, and that these motors need to be run hot so as to alleviate fouling of the plugs. This last bit was the reult of me asking his advice on running the thing without the therm to see what effect that had on the temp.

So with this new information, not doubing any of the above, I put things back together and tested. Same thing....I had hot water from the exhaust port under the head but this time I was armed with a temperature prob to measure the temp. I can get 58oC but this is probably not a vey accurate fiqure in as much as I should be taking that reading from some sort of container rather than just placing the probe under the outlet.

I'm intending to put the boat in the water tonight for a more accurate test, testing with muffs isnt perhaps the most idea way of gauging these things so hopefully all is as it should be.