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Main causes of engine overheating and how to check and rectify

Geoff Cooper

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2006
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AR
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Thought i would try to shed a little light on the usual causes of engine overheating and how you can check if there could be a problem and if so the way to check and rectify, Firstly if your boat is fitted with valves that allow you to close the water input to one engine and the valves are only very slightly smaller than the actual hose this can be one cause as the ECU picks up on this, The way you can tell is if you open the boat up for about 5 minutes on high revs around 9 or 10,000 and all of a sudden your overheating lights come on that's usually the reason, It will close the engine down or go into limp mode until the engine cools down, Reason number 2 is i know these Jetboats can get into shallow water and we all love being able to step off the stern without swimming to the beach but you would be amazed how much sand and small stones are sucked up into the inlets just on tick over, These go into the engine block and if they don't pass through they block the water injectors and cause overheating in the exhaust outlet and cause damage to the rubber exhaust outlet pipe, Again this can be changed reasonably easy just get a friend to give you a hand it's about an hours work, If this pipe splits it will cause the engine compartment to fill with hot water so remember if you get water in the engine compartment and its hot it's coming out of the engine if it's cold it's coming from outside.

I had a customer recently that had overheating problems and as i was busy and he couldn't wait he took his boat to Yamaha agent who identified the problem as a catalytic converter so they changed it and the boat was still the same so they pulled the jet pumps and they were ok so the refitted the jet pumps and gave it back to him and said it must need a new computer, You can imagine the size of the bill he got, I got the boat and first thing i checked was the inlet pipes and removed the valves and fitted new hoses after checking around we took the boat out and job done no overheating lights flashing and engine didn't cut out it cost about $20 Yamaha charge about $1000 and fitted thing's that weren't necessary, Below are some tips and photos if your interested.

20211130_125157.jpg

Ok if you get hot water in your engine compartment this is most likely where its coming from, This part is where gases from the engine are cooled by water injected into the pipe, This is no more than an aluminium cover that's in 2 parts a top and a bottom just held together by screws so you can remove the cover which then exposes the rubber pipe, It has 2 clips one at each end so remove the clips and with a little luck you can push the pipe backwards to allow you to remove it, It's connected to a pipe into the tanks and there normally enough room to remove it without going into the stern compartment but if you have to just remove the 2 straps that hold the tank in place and slide it back you only need an inch or 2.

20211130_125031.jpg

The first arrow shows a hole in the cover that a small pimple on the new pipe locates into, It's a good idea to change the clamps at the same time don't forget use stainless.

20211130_130646.jpg

This is another locating piece that goes into the metal exhaust itself.

20211130_130656.jpg

You cant go wrong as it tells you which way it goes

20211130_130716.jpg

This is usually the cause of the problem with hot water in the engine compartment, Open the engine compartment and get someone to drive the boat slowly and take a flash light and look underneath this pipe and see if you can spot the leak, Look at the pipe above the spit and you can see the pimple that locates into the hole on the aluminium cover.

20211130_130759.jpg

You can see the ridge where the aluminium pipe butts up to the rubber pipe i use a Gasket sealer and squeeze a reasonable amount all around where it butts up then leave it for 24 hours to go off properly some gasket sealers will do 600 degrees so just check before you buy one, Don't use silicon.

Ok well i hope that helps and it's a straight forward job i have done it alone before now but on the odd occasion i had someone to push the tank end of the pipe forward as the new pipe can be a little tight and also make sure you use sandpaper and clean where the joints go onto the pipe, The new rubber pipe isn't expensive and it's not a bad job to do, Ok hope that helped and take care.
 

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Scottintexas

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great to see a geoff cooper post, thanks for sharing !

I would have thought with how resourceful Thai people are they would have figured this out but I guess at a dealership the boss is more worried about making money
 

Cobra Jet Steering LLC

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In the U S A avoid using the word torch lol " lol means it was a joke"
 

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Geoff Cooper

Jetboaters Admiral
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Location
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2006
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AR
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23
great to see a geoff cooper post, thanks for sharing !

I would have thought with how resourceful Thai people are they would have figured this out but I guess at a dealership the boss is more worried about making money
Yes that's the problem Scott and they use young lads who have little experience and pay they about $10 a day which is the minimum wage here.
 

RobbieO

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Thought i would try to shed a little light on the usual causes of engine overheating and how you can check if there could be a problem and if so the way to check and rectify, Firstly if your boat is fitted with valves that allow you to close the water input to one engine and the valves are only very slightly smaller than the actual hose this can be one cause as the ECU picks up on this, The way you can tell is if you open the boat up for about 5 minutes on high revs around 9 or 10,000 and all of a sudden your overheating lights come on that's usually the reason, It will close the engine down or go into limp mode until the engine cools down, Reason number 2 is i know these Jetboats can get into shallow water and we all love being able to step off the stern without swimming to the beach but you would be amazed how much sand and small stones are sucked up into the inlets just on tick over, These go into the engine block and if they don't pass through they block the water injectors and cause overheating in the exhaust outlet and cause damage to the rubber exhaust outlet pipe, Again this can be changed reasonably easy just get a friend to give you a hand it's about an hours work, If this pipe splits it will cause the engine compartment to fill with hot water so remember if you get water in the engine compartment and its hot it's coming out of the engine if it's cold it's coming from outside.

I had a customer recently that had overheating problems and as i was busy and he couldn't wait he took his boat to Yamaha agent who identified the problem as a catalytic converter so they changed it and the boat was still the same so they pulled the jet pumps and they were ok so the refitted the jet pumps and gave it back to him and said it must need a new computer, You can imagine the size of the bill he got, I got the boat and first thing i checked was the inlet pipes and removed the valves and fitted new hoses after checking around we took the boat out and job done no overheating lights flashing and engine didn't cut out it cost about $20 Yamaha charge about $1000 and fitted thing's that weren't necessary, Below are some tips and photos if your interested.

View attachment 167738

Ok if you get hot water in your engine compartment this is most likely where its coming from, This part is where gases from the engine are cooled by water injected into the pipe, This is no more than an aluminium cover that's in 2 parts a top and a bottom just held together by screws so you can remove the cover which then exposes the rubber pipe, It has 2 clips one at each end so remove the clips and with a little luck you can push the pipe backwards to allow you to remove it, It's connected to a pipe into the tanks and there normally enough room to remove it without going into the stern compartment but if you have to just remove the 2 straps that hold the tank in place and slide it back you only need an inch or 2.

View attachment 167740

The first arrow shows a hole in the cover that a small pimple on the new pipe locates into, It's a good idea to change the clamps at the same time don't forget use stainless.

View attachment 167746

This is another locating piece that goes into the metal exhaust itself.

View attachment 167743

You cant go wrong as it tells you which way it goes

View attachment 167744

This is usually the cause of the problem with hot water in the engine compartment, Open the engine compartment and get someone to drive the boat slowly and take a flash light and look underneath this pipe and see if you can spot the leak, Look at the pipe above the spit and you can see the pimple that locates into the hole on the aluminium cover.

View attachment 167745

You can see the ridge where the aluminium pipe butts up to the rubber pipe i use a Gasket sealer and squeeze a reasonable amount all around where it butts up then leave it for 24 hours to go off properly some gasket sealers will do 600 degrees so just check before you buy one, Don't use silicon.

Ok well i hope that helps and it's a straight forward job i have done it alone before now but on the odd occasion i had someone to push the tank end of the pipe forward as the new pipe can be a little tight and also make sure you use sandpaper and clean where the joints go onto the pipe, The new rubber pipe isn't expensive and it's not a bad job to do, Ok hope that helped and take care.
Is this something that should be done at certain intervals as preventative maintenance?
 

Geoff Cooper

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It's easy to check just open your boat up to around 9000 rpm and wait a few minutes and see if the warning lights start to flash, If you generally don't exceed 7 to 8000 rpm you probably would never have known and if you don't have a hot water leak in the engine compartment then there's nothing to worry about, This is mainly caused by taking the boat into shallow water or if you have fitted valves in the intake pipes and they are slightly small as i said before.
 

Julian

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