Over Heating AD31's

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Liselle

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Over Heating AD31\'s

We have a very strange random overheating issue on our twin AD31's. 1st one engine then the other. It has happend on the last few occasions.
I always check the raw water filters before every trip, they are nearly always clear.
The 1st time we had just got onto the plane when the starboard engine alarm sounds and the guage is off the scale, I shut it down limp home on one engine. I check the filter its clear, lift the drive its clear. next trim out fine.

Out again, the other engine starts overheat. limp home

I get volvo man round, initially the non volvo impellers appear to be a bit soft, so we change them. strip the heat exchanger looks fine, strip the exhast elbow looks fine.

Out again, over the next two days fine, until the trip home, one engine overheats, back off the revs to tickover, soon cools down, back on the plane, all fine 10 mins later the other engine starts to overheat, cant believe this, back them both off soon cools down, limp home. Still no obvious obstructions in the filter.

Any ideas, bearing in mind that each engine is completely independent.
 
Re: Over Heating AD31\'s

My AD31 overheating problem was the water intakes being clogged with barnacles; it doesn't take much (i.e. I agree with Davido). Have you recently done anything to the engines like renew the coolant? If so, perhaps the anti-freeze was the wrong type? If the boat bottom is dirty, that can also put more load on the engines.
 
Re: Over Heating AD31\'s

No, havent changed any coolant, I checked the intakes over the back as best as I could , not obviously restricted. Its the one day its fine the next it isnt bit I cant understand.
 
Re: Over Heating AD31\'s

Isnt there also an intake through a sea cock? thats where i was thinking. The fact its a random fault could be down to load, ambient temperatue anything, just sounds like insufficuent cooling to me.
 
Re: Over Heating AD31\'s

It'd be worth checking the thermostats if you've not already done so. I had the reverse problem with one of my AD31s; the thermostat was gunked up and couldn't close completely hence running too cool. If yours are gunked up it could be they are struggling to open up properly. Must admit a long shot as each engine has two and it's hard to imagine they're all gunked up, but you never know.....
 
Re: Over Heating AD31\'s

are you on a drying mooring by any chance? we have had 2 boats with volvo's, one with AD31's and one with kad32's they bot occasionaly suffered from air locks causing temps to soar. The cure was to crack open the raw water filter lids when the engine is up and running, it will cause a burst of water into the bilges but gets rid of the air lock.

If you are not on a drying mooring then I have no clue other than the usual things like bags over inlets etc.
 
Re: Over Heating AD31\'s

The blockages on mine weren't obvious either; I had to resort to lifting the drives and then getting in dinghy and reach over; the intake holes are very small.
 
Re: Over Heating AD31\'s

Are you absolutely sure the engines are getting hot, as they are not interconnected and the overheat is showing randomly on alarms or gauges, could it not be electrical gremlins at work??
 
Re: Over Heating AD31\'s

I had a persistant over heat problem on my last boat. After stripping and cleaning the entire system it turned out to be a bad earth on the guage. Have a look at that first before you spend serious dosh replacing bits. /forums/images/graemlins/smirk.gif
 
Re: Over Heating AD31\'s

At this point in the season I am drawn to the water intakes, its due to be lifted in a few weeks. I just thought if it were the intakes then surely it wouldnt be so random, as far as the gauges are concerned, separate engines separate gauges, both malfunctioning with the same fault, bit too much of a coincidence surely? I quizzed the marine engineer about the thermostats, he seemed pretty sure that if the thermostats were faulty then it would have spat the freshwater coolant everywhere during the overheat, those levels are still un moved.

Its not on a drying mooring by the way.
 
Re: Over Heating AD31\'s

agreed separate gauges but maybe a common earth, remember when you have seen an elderly car put the indicators on and the brake light flashes as well - two separate lights but a common dodgy earth -just my five penneth for what its worth!!
 
Re: Over Heating AD31\'s

Hi Kevin
Apart from over heating everything OK, haven't sold her yet, the boat I mean not SWMBO!
Totally agree about those pesky barnacles being the problem for the overheating, they seem to have gone mad this year getting in all sorts of places I have never seem them in before, so that would be my bet and you state the boat is coming out soon so you will know then. Let us know the outcome please.

Steve
 
Re: Over Heating AD31\'s

Steve, thanks for the reply, I guess I will have to wait and see what the lift shows up ( 12 Nov). I will let you know.
 
Re: Over Heating AD31\'s

When you remove lid of raw filter unit is it full of water or empty?
After the alarm went off did you remove filter lid to see if any water in the container and then tried filling the raw water filter with a bucket of sea water to "prime" the pump and then briefly run engine and see if temps go down.
If your impellors are worn or air leak in system the above may get water circulating again to get home and/or enable you to use boat..
This temporary fix can keep you "cool" for ages until you sort the problem properly .
 
Re: Over Heating AD31\'s

we have had similar on AD41's and KAD 32's with the air lock being to blame. we were told and it worked for us that if at cruise rev's and guage starts to rise a quick blast at full rev's will also bring temp down, this increases the suction apparently. Sounds wierd but works. Obviusly if no quick response on guages don't keep her up there with a hot engine.Also the plate for the impellor housing wares as does the seal on the lid/ filter basket again lessening the suction
 
Re: Over Heating AD31\'s

My engineer is going to replace the seals on the baskets as its a quick and cheap thing to do, although they do look fine. I think Wifey who is almost suicidal when the engines overheat, opening the throttles to full would probably finish her off
 
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