Outboard Motor Overheating

Wildbill

Wildbill

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i know it's not motorhome related Scratching my head with this one we have a boat with a 9.8 HP outboard mercury long shaft it start runs OK we have changed the impeller but its still overheating seem to be plenty of water getting through thing is how much is not enough ?
bill
 
Blocked channels? Had the problem with rescue boat outboards that had not been thoroughly flushed with fresh water after salt water use.... corrosion gummed everything up
 
DuxDeluxe said:
Blocked channels? Had the problem with rescue boat outboards that had not been thoroughly flushed with fresh water after salt water use.... corrosion gummed everything up
Click to expand...
Totally right. There are many cooling channels and if you run the engine in saline water then let it sit in warm summer conditions, the water will evaporate leaving a deposit of salt crystals that eventually block the cooling to part of the head and you overheat.

Try flushing with some of this, or something similar.

Descaling Motor Flush

Starbrite quality care products since 1973 for: Automotive, Marine, Aviation, Motorcycle, Powersports, Outdoor Power Equipment, ATV, Snowmobile, Home Care, Outdoor Furniture, Farm Implement.
www.starbrite.com www.starbrite.com
 
As above blocked cooling channels from a poor or no freshwater flush at the season end.

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General consensus, first stop a good de-scale. We kept a 40 Gall drum of fresh water lashed near the "Jolly" boat, davit. Used to clamp the old "Seagulls" to the side and run for a few min after use in sea water. That was the Apprentice or Cadet Job`!.
 
sorted back flush it with impeller out with pressure washer replaced impeller then put it in a drum of fresh water on the stand and ran it improved over about ten min we them changed the water and used abut 2 kg of citric acid ran it for abut 20 min it's got rid of loads of crap changed the water and its bean ruining abut a hr now and no singe of over heating now have a hose ruining in to tank changing water before drooping a bit of bicarb in to neutralist any residual acid look like job done
bill
 
Last edited:
ManTheVan said:
Totally right. There are many cooling channels and if you run the engine in saline water then let it sit in warm summer conditions, the water will evaporate leaving a deposit of salt crystals that eventually block the cooling to part of the head and you overheat.

Try flushing with some of this, or something similar.

Descaling Motor Flush

Starbrite quality care products since 1973 for: Automotive, Marine, Aviation, Motorcycle, Powersports, Outdoor Power Equipment, ATV, Snowmobile, Home Care, Outdoor Furniture, Farm Implement.
www.starbrite.com www.starbrite.com
Click to expand...
thank you we just used citric acid that got all the crap out now all flushed out and ruining lovely the was a lot of rubbish in the the drum but now ruining cooler can't complane for a engine we have taken a chance on £80 spares or repair i did have confidence i could fix it set abut it this-morning all sorted now it will only be used in fresh water now anyway canals revers
bill
 
sallylillian said:
As above blocked cooling channels from a poor or no freshwater flush at the season end.
Click to expand...
It sat for five years in a garage so that enplanes why it had issues it Ben ruining hasn't missed a beet full tank of fuel ruining clean as a two stroke can wounder how many gallon a hre under load it will burn suppose that will all have to do with displacement and all that malarkey.
Now to get my engine from bodmin with a same problem

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Wildbill said:
wounder how many gallon a hre under load it will burn suppose that will all have to do with displacement and all that malarkey.
Click to expand...

The rule of thumb for outboards is 10% of the horse power per hour in gallons. So a 9.9hp will use about 1 gallon per hour at full throttle.

We had 2 x 250hp on the club boat..... don't work out our fuel consumption! Although being in the Middle East it was only 60p a gallon.
 
another one it two stroke i have tried to avoid them most of my life apart from a moped when a young lad that was nothing but bother
anyway it seem to back fire through the exhaust thinking Ilene mixture or wrong plug gap am i right ?
 
Could be timing if it is back firing. Or too rich.

Someone cleverer than me said.....

'A backfire out the exhaust is generally the result of the engine failing to ignite the air/fuel mixture for several revolutions. The air/fuel mixture passes through, filling the exhaust system with a burnable mixture. Then the cylinder does fire and it ignites all the fuel in the exhaust. '

So could be plug gap or bad sparkplug lead etc.
 
Neil Bedwin said:
Could be timing if it is back firing. Or too rich.

Someone cleverer than me said.....

'A backfire out the exhaust is generally the result of the engine failing to ignite the air/fuel mixture for several revolutions. The air/fuel mixture passes through, filling the exhaust system with a burnable mixture. Then the cylinder does fire and it ignites all the fuel in the exhaust. '

So could be plug gap or bad sparkplug lead etc.
Click to expand...
Sorted it bad connection on the coil pack its running lovely now
thank's for your reply
bill
 

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