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Overheating Engine


IndianChick

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Is it indirectly cooled as in it takes and returns its cooling water from the canal/river? Is this a recent problem, or has it always behaved thus in your experience?

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A couple of questions immediately apring to mind:

 

1) How much time on full throttle does it take for the warning light to come on? Is it immediate or only after ten or twenty minutes?

 

2) Has it always done this or is it a recent/new problem? Or have you just bought the boat?

 

I imagine you refilled with coolant after changing the impeller! Or was that a raw water pump impeller you changed it on?

 

Ok, three questions!

 

MtB

 

 

P.S. Welcome to the forum :)

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It is indirectly cooled and has an exchange heating system too. I have just bought it and it hasn't been on the cut since April so it was her first run in a long time.

I had a similar setup on a previous boat. It drew the cooling water through a "mud box" which (as the name suggests) filled with mud after a while, and would reduce the efficiency of the cooling system. I would be looking here personally and cleaning it out (if indeed it has a mud box) apart from the obvious: Is the coolant at the correct level? Any airlocks? etc.

Edited to add: Welcomre to the forum, and I just remeberd I had tochange the cover on the raw water pump as well as the impeller, as this can have an effect on the efficiency of the pump.

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Is it physically losing water? If it is & assuming you have an expansion tank in the cooling system, you might want check the system's filler cap. If it's on top of the engine, it'll look like a normal radiator cap, but it won't have a spring valve. These caps will lose their seal over time & coolant will seep past until you overheat.

 

Tip: don't try & buy the cap, or any other radiator cap, from Halfords. They don't stock them, & besides, they're incapable of determining any part without a car registration! Don't get me going on filter equivalents, that's another story. Basically, Halfords are crap for boaty bits.


Ah. Since I submitted this, you have revealed you have an indirect system. I have zilch experience of those, so ignore me!

Edited by Spuds
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Is it physically losing water? If it is & assuming you have an expansion tank in the cooling system, you might want check the system's filler cap. If it's on top of the engine, it'll look like a normal radiator cap, but it won't have a spring valve. These caps will lose their seal over time & coolant will seep past until you overheat.

 

Tip: don't try & buy the cap, or any other radiator cap, from Halfords. They don't stock them, & besides, they're incapable of determining any part without a car registration! Don't get me going on filter equivalents, that's another story. Basically, Halfords are crap for boaty bits

Indirect? Ok, ignore me!

 

Most chandlers are crap at car parts too...

 

And then there's the pub with the arrangement with the local bank. The bank agree not to sell beer and the pub doesn't cash cheques...

 

:D

 

 

Anyway, this isn't helping Indianchick!

 

 

MtB

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Thanks Mike! I started her steady and she was fine, however when I put her on full throtle the warning came pretty much instantly. I think it is a raw water pump impeller but I will check the coolant tonight.

 

Hmmmm there are two separate possibilities. The engine could be genuinely overheating OR, the red warning light is faulty.

 

Does the red light go out again if you reduce the engine speed back to 'steady'?

 

 

MtB

Hi Catweasel, the mud box was my first port of call. It was reasonably OK, just stones which I have now cleared. I will try the coolant cap.

 

Thanks everyone for your help! I'm new to forums so not sure how to reply to individuals so please bear with me!

 

 

Click on the 'Quote' button, bottom right of the post you want to reply to...

 

MtB

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Hmmmm there are two separate possibilities. The engine could be genuinely overheating OR, the red warning light is faulty.

 

Does the red light go out again if you reduce the engine speed back to 'steady'?

 

 

MtB

 

 

Click on the 'Quote' button, bottom right of the post you want to reply to...

 

MtB

Thanks Mike! I didn't reduce the speed, I just turned it off to be on the safe side. I will try that out too and get back to you. Thanks!

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It is indirectly cooled and has an exchange heating system too.

 

This means there are two water circuits. It is possible one circuit works fine, but the other one doesn't.

 

I suspect you have air or an air lock in the engine circuit

 

Richard

  • Greenie 1
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Thanks Mike! I didn't reduce the speed, I just turned it off to be on the safe side. I will try that out too and get back to you. Thanks!

You need to let the engine tick over to cool, spredding the heat evenly through the engine.

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I had a similar problem with my boat when I bought it. It hadn't been used for months. The temperature warning light came on from time to time when the water temperature was normal. The culprit was the temperature sender which probably through lack of use, had got a bit sticky. Put it in some near boiling water, cleaned it up, it's been fine since. I'm not saying this is your problem, the other posters on here know far more than I do, but it's a possibility!

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Has the raw water sea cock been turned on?

 

(Assuming the set up has one of course!)

 

This is a good point. A raw water cooled engine will take about 20 mins to boil with the sea cock turned OFF.

 

I know this from personal experience as does, it appears, Naughty Cal!

 

MtB

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If your raw water is going back into the canal via the exhaust (or maybe if it goes through a separate skin fitting, see below) please make sure lots of water is cuffing out of the exhaust. Many of these smaller "yachty" type engines have a temperature sensor on the raw water exhaust mixing elbow, not that I can see one in Richards pictures) and these tend to light a light and sound the buzzer if the raw water flow is not sufficient to keep the exhaust temperature down. If the engine has been modified to dry exhaust this sensor needs disconnecting.

 

I note that you have not been able to tell us if the engine actually overheats or if its just the warning comping on. Its not that easy to check so can you borrow an infra-red thermometer to actually measure the cylinder head or thermostat housing temperature.

 

The advice about the mud box and sea cock is good and should be checked first. If the exhaust steams or the water flow reduces at high speeds t would be worth thinking about a possible blockage in the exhaust. Either a furred/scaled up mixing elbow or a burned and eliminating exhaust hose lining - even a rag left stuffed in the exhaust hose in the past.

 

I expect you changed the raw water pump impeller. The cover gasket thickness is critical (unless it uses an O ring). Too think and the pump will suffer reduced capacity. Did you inspect the cover for wear? Both the cover and the base of the pumping chamber are subject to a "groove" under the cam. This again can reduce pump capacity. Did you check the pump shaft for "rock" in its bearings. Some older Volvo Penta raw water pumps had the shaft running in the pump body rather than a bearing so when the body wears the pump can suck air up the shaft rather than water out of the canal. There is also one or two "oil" seals in many pumps and if the one closest to the impeller wears again the pump can suck air.

 

Make sure all the hose joints between the raw mud box and pump are airtight.

 

It would also be worth taking any hose elbows in the raw water system off to make sure no old impeller wings are caught in the bend. Likewise if the history of the boat is unknown it may be a good ides to take the ends off the heat exchanger to make sure years of neglect has not allowed them to become clogged with muck that has got past the mud box.

 

Do not go messing about with the exhaust unless either everything else is known t be OK or you are suffering from a reduced water flow, especially at high speeds and powers.

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Not familiar with that engine, but...

 

If the light comes on when revving and goes out when at idle, it could be a pressure/vacuum sensor to tell the raw water is blocking.

 

In which case it could be a blockage elsewhere like a kinked or crushed hose, or even the sensor itself though less likely.

 

A competent and reputable boat yard engineer should be able to sort it, or a boating friend/neighbour similarly skilled.

 

cheers, Pete.

~smpt~

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If your raw water is going back into the canal via the exhaust (or maybe if it goes through a separate skin fitting, see below) please make sure lots of water is cuffing out of the exhaust. Many of these smaller "yachty" type engines have a temperature sensor on the raw water exhaust mixing elbow, not that I can see one in Richards pictures) and these tend to light a light and sound the buzzer if the raw water flow is not sufficient to keep the exhaust temperature down. If the engine has been modified to dry exhaust this sensor needs disconnecting.

 

I note that you have not been able to tell us if the engine actually overheats or if its just the warning comping on. Its not that easy to check so can you borrow an infra-red thermometer to actually measure the cylinder head or thermostat housing temperature.

 

The advice about the mud box and sea cock is good and should be checked first. If the exhaust steams or the water flow reduces at high speeds t would be worth thinking about a possible blockage in the exhaust. Either a furred/scaled up mixing elbow or a burned and eliminating exhaust hose lining - even a rag left stuffed in the exhaust hose in the past.

 

I expect you changed the raw water pump impeller. The cover gasket thickness is critical (unless it uses an O ring). Too think and the pump will suffer reduced capacity. Did you inspect the cover for wear? Both the cover and the base of the pumping chamber are subject to a "groove" under the cam. This again can reduce pump capacity. Did you check the pump shaft for "rock" in its bearings. Some older Volvo Penta raw water pumps had the shaft running in the pump body rather than a bearing so when the body wears the pump can suck air up the shaft rather than water out of the canal. There is also one or two "oil" seals in many pumps and if the one closest to the impeller wears again the pump can suck air.

 

Make sure all the hose joints between the raw mud box and pump are airtight.

 

It would also be worth taking any hose elbows in the raw water system off to make sure no old impeller wings are caught in the bend. Likewise if the history of the boat is unknown it may be a good ides to take the ends off the heat exchanger to make sure years of neglect has not allowed them to become clogged with muck that has got past the mud box.

 

Do not go messing about with the exhaust unless either everything else is known t be OK or you are suffering from a reduced water flow, especially at high speeds and powers.

Thanks for your comprehensive advice Tony! Will definately give it all a try.

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  • 2 weeks later...

Thank you everyone for all your help. The filter coming out of the mud box was blocked. The problem has been temporarily fixed but I took her out on the cut at the weekend and the problem came back. So back to the drawing board so to speak and go through a process of elimination. Happy boating everyone! boat.gif

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Thank you everyone for all your help. The filter coming out of the mud box was blocked. The problem has been temporarily fixed but I took her out on the cut at the weekend and the problem came back. So back to the drawing board so to speak and go through a process of elimination. Happy boating everyone! boat.gif

 

 

Interesting.

 

Has the mud box blocked again perhaps? Is this the problem that has returned, or did you mean this time the mudbox filter remains unblocked but the overheating persists?

 

Where does the raw cooling water leave the boat? Via the exhaust or via a skin fitting? Look and see if there is a healthy flow of water. If not, and the mudbox filter is definitely still clear the new impeller you fitted probably got cooked/knackered by the previous blockage of the filter...

 

MtB

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