Overheating AD31

[steve157]

Hi, am having big problems with one of the engines as it keeps overheating and have now run out of ideas if anyone can help it would be great.
Symptoms are the engine will idle all day but as soon as the revs build under way the engine overheats. Have had a look at the impeller which looks ok and there is flow being exhausted out of the leg. I thought it might be the thermostats so changed these still no better. Thought it might be a air lock as have changed the calorifier but the flow and return pipes are hot and the water is heating up so am completely stuffed.
Do you think I should bypass the hot water tank to eliminate that just in case as that's the only thing Ive done lately.

 

[Dave_Seager]

I am not familiar with your engines but have the older AQD32As. These have oil coolers which can easily be blocked by weed and cause overheating.
Hope this helps.

 

[[2068]]

Scaled up heat exchanger?
Kinks or weak/collapsing hoses? (esp from outdrive pickup to transom shield).

It could be that your cooling system was marginal in the first place, and the new calorifier (not scaled up, nice clean new internal pipes) is diverting just that bit more water off than the old one to cause a problem.

dv.

 

[studgies]

our last boat had AD31's and we had the same issue. As said, check the raw water heat exchanger, we cleaned ours out with brick cleaner which did wonders. NExt check the exhaust elbow, they have a habit of rusting up, at idle water flows through but they get too blocked to allow water out when at higher revs. We removed ours, treated them to the brick clener treatment over night then used various implements to scrape arouind inside them to get all of the rust scale out.

One last issue we had was after headinf off down river one engine would start to run hot, we found cracking off the raw water strainer cover caused a burst of water and air to escape and cured the problem. Our mooring dries and it seems that engine had a problem with air locks.

Hope this may help a little

 

[RIN]

Do you have a separate temp guage and alarm? If so, did the alarm go off or did you notice that the temp had gone up or both?

 

[johnnys]

We had the same problem with our AD31's when we had a Sealine. Heat exchangers were partly furred up, engineer said it was a common fault. Fairly simple job to clean them out, no more trouble.

 

[steve157]

Thanks guy few more things to look at there, re the temp/ alarm question...No alarm just temp gauge and a bilge full of coolant!!!!...

 

[strakeryrius]

Had a similar problem beginning of last year - starboard engine overheating after running up to temp and also thowing belts far too often. Volvo said it was due to tappets being overdue for adjustment (previous owner's mechanic suffered from the manana syndrome). She has run sweet as a nut ever since then.

 

[scottie]

yes bypass the hot water because until you check it it will be at the back of your mind
it might also be worth changing the impeller as visual inspection is not always the answer

 

[Liselle]

We, had similar issues towards the end 2008 with our twin AD31's. Ours was a very strange one, as either engine would start to overheat, in turn, on the same trip. We had the heat exchangers checked, they were clear, the exhaust elbows were clear. Since then I have had the valve clearances checked and set, impellers changed plus my engine guy did also change the strainer seals, and said to make sure the tops are nice and tight after checking, because if a seal is not maintained then air locks can form and restrict the flow.

Unfortunately, we didnt get much of a chance to test them after that, just one trip, seemed fine. The boat was then lifted for the winter.

We did notice a few more that normal barnacles around the water intakes, we are hoping that perhaps these were the cause, as it was late in the season and we never had any problems at all earlier in the year.

Apart from the strainer seals, I know this may not be much help.

 

[Wiggo]

[ QUOTE ]
We did notice a few more that normal barnacles around the water intakes, we are hoping that perhaps these were the cause, as it was late in the season and we never had any problems at all earlier in the year.

Apart from the strainer seals, I know this may not be much help.

[/ QUOTE ]
I do remember a couple of years back some form of barnacle or mussel (Zebra?) being a problem in some UK waters as they grew like buggery and could even block intakes.

 

[davedpc]

If all else fails i would do a compression test,if its a head gasket it will overheat especially at w.o.t