Volvo Penta Saildrive cooling issue

[RJO]

I have a Hunter Horizon 26 with a 2001 Volvo Penta 10hp sail drive. Having experienced overheating issues, particularly at moderate and high rpm, I have replaced the water pump and impeller and have also bought a new exhaust elbow to replace an old one which was heavily carbonised and cracked. However, the problem persists and I am advised that this may relate to a lack of water circulation caused by barnacle growth inside the sail drive. Certainly, some water comes out of the exhaust alongside a lot of steam.
One suggestion that I have had from the local sailing community is to supplement the water intake via the sail drive by either adding a new sea cock and connecting to the cooling system via a T piece, or taking a supply from the existing toilet sea cock.

Any thoughts or advice would be gratefully received.

 

[Spirit (of Glenans)]

Yes, if you can fit an independent seacock your problem will probably be solved, but first you can try to cure the blockage; - at the bottom of the saildrive you will find a hole, just under the leading edge. If you get a piece of rebar, (8mm, I think, from memory), a few inches longer then the saildrive leg, poke it up as far as it will go and swirl it around a bit, you will break up a lot of the undesired aquatic life. I have found that this procedure generally worked for me , but a couple of years ago I experienced some mystery overheating which I eventually realised was being caused by a blockage in the supply, even though I thought I had cleaned out the inlet port. As the boat was in the water I tried unsuccessfully to rod it from inside, by taking off the hose and put on a short piece of hose to prevent water ingress. I eventually got it unblocked by blowing down the hose, ( more pressure could be applied with a dinghy pump).

 

[RJO]

Yes, if you can fit an independent seacock your problem will probably be solved, but first you can try to cure the blockage; - at the bottom of the saildrive you will find a hole, just under the leading edge. If you get a piece of rebar, (8mm, I think, from memory), a few inches longer then the saildrive leg, poke it up as far as it will go and swirl it around a bit, you will break up a lot of the undesired aquatic life. I have found that this procedure generally worked for me , but a couple of years ago I experienced some mystery overheating which I eventually realised was being caused by a blockage in the supply, even though I thought I had cleaned out the inlet port. As the boat was in the water I tried unsuccessfully to rod it from inside, by taking off the hose and put on a short piece of hose to prevent water ingress. I eventually got it unblocked by blowing down the hose, ( more pressure could be applied with a dinghy pump).

Many thanks for your advice on this. I did try a wire coat hanger to clean out the sail drive but it didn't have much effect. I'll try again with the rebar.

 

[TrampBg]

Most Volvo Penta 20XX series engines are with direct cooling (some are equipped with indirect cooling- heat exchanger). Are you sure that water passages of the block and engine head are free? You can try to put shore length of hose from the intake port of the raw water pump in a bucket with water and if the flow from the exhaust elbow is OK then to continue with checking the water passage of the sail drive. Unfortunately for some reason, barnacles like the dreaded old style sail drive valve (with the blue plastic handle) and it is very difficult to remove them while the boat is in the water but is not impossible. Good luck!

P.S.
Sorry for my English.

 

[RJO]

Most Volvo Penta 20XX series engines are with direct cooling (some are equipped with indirect cooling- heat exchanger). Are you sure that water passages of the block and engine head are free? You can try to put shore length of hose from the intake port of the raw water pump in a bucket with water and if the flow from the exhaust elbow is OK then to continue with checking the water passage of the sail drive. Unfortunately for some reason, barnacles like the dreaded old style sail drive valve (with the blue plastic handle) and it is very difficult to remove them while the boat is in the water but is not impossible. Good luck!

P.S.
Sorry for my English.

That's fine - many thanks. I did wonder whether it would help to flush the system with furnox or something similar?

 

[penfold]

Rydlyme is the preferred unction for fettling clag out of the cooling passages, which appears to be a form of buffered hydrochloric acid.

 

[Rustyknight]

If you look at this link, part number 25 may be the culprit.

Volvo Penta Exploded view / schematic Cooling Syst, Induction and Exhaust Manifold. Seawater-cooled Engine. 2001, 2001B, 2001AG, 2001BG, 2002, 2002B, 2002AG, 2002BG, 2003, 2003B - MarinePartsEurope.com

All the water from the water pump passes through it, and most goes straight to the exhaust elbow. Water gets into the cooling block through a single hole in the underside of the pipe..... from memory it's about 4 or 5 mm diameter. Over time, this hole can be reduced by scale, meaning the block can overheat, causing a lot of steam from the exhaust.

This pipe can be removed by undoing the clamps, and by using a punch to remove it from the block, and either replaced by a new one, or cleaned up and reinstalled..... as long as it hasn't been damaged during removal. On refitting, the hole must be facing down.

Apologies for what might read as poorly explained. If you have a workshop manual it should have a better diagram and explanation.....

 

[Daydream believer]

To test the sail drive flow disconnect the hose, open the valve & see how much water flows through. You might also find the blockage is actually at the seacock so some work with a length of stiff wire whilst the water is gushing in may be worth a try. Check the filter is clean first of course.
Then get a large tub plus some buckets of water. Put the hose in that & top the tub up from buckets. see if the flow changes. You can compare flow rates, tub/saildrive
If you are happy that there is no difference between tub supply & saildrive supply I would look at the pump. Is the impeller OK? The cover plate may be worn & you could be loosing suction . See if it can be reversed. If so scrape the paint off & reverse it. That may well solve the issue. You can buy a new plate, or make your own . I can tell you how.
Of course you may still have to follow all the earlier posts about cleaning ports etc but my points are easily done & are outside the engine & easily undertaken first.

 

[Tranona]

Unlikely to be shortage of water coming up the saildrive. There is plenty of capacity, even if partially blocked - the same drive (and water supply) is used on much larger engines. Easy way to check is to shut the valve, remove the hose and open the valve. You should get a jet of water coming in.

The 2001 is well known for marginal cooling, particularly under high loads made worse by scaling over time as post#7 describes. You may also consider using Rydlyme to descale the water passages
Biodegradable Marine Descaler & Cleaners - RYDLYME Marine Readily available in many chandlers
It is possible to add an independent seacock, sometimes with a T and a valve so you ahve a choice, but it really is an unnecessary complication.

 

[TrampBg]

Agree with the above. Water passage of the saildrive 120S is pretty wide - roughly half the width of the lower part (but the valve is only about 1/2 inch).
It is also worth checking the thermostat- on raw water cooled engines it may corrode in closed position thus restricting the water flow to the coolant pipe (with one entry hole of about 5mm and multiple distribution holes with smaller diameter).
Checking the raw water pump's cover and eventually reversing it is good advice.

 

[Rustyknight]

As it's close to 15 years ago since I did the job my memory is a little hazy. On reflection, I think the hole I mentioned is closer to 3mm or 3.5mm than the 4 to 5mm I mentioned earlier, which is why it's liable to get scale building up and blocking it.

To remove the pipe is fairly straightfoward. One end has a flange on it, so it can only be driven out one way. The very act of driving it out may be enough to scrape the scale off. I did think of drilling the hole slightly bigger, as I had read of a few other 2001 owners with the problem doing, but I was happy with just fitting a new pipe... as was the engine.

 

[RJO]

Rydlyme is the preferred unction for fettling clag out of the cooling passages, which appears to be a form of buffered hydrochloric acid.

Serious stuff then and more suited to the job than furnox central heating cleaner. I'll purchase some and see how I get on - many thanks for the advice.

 

[RJO]

If you look at this link, part number 25 may be the culprit.

Volvo Penta Exploded view / schematic Cooling Syst, Induction and Exhaust Manifold. Seawater-cooled Engine. 2001, 2001B, 2001AG, 2001BG, 2002, 2002B, 2002AG, 2002BG, 2003, 2003B - MarinePartsEurope.com

All the water from the water pump passes through it, and most goes straight to the exhaust elbow. Water gets into the cooling block through a single hole in the underside of the pipe..... from memory it's about 4 or 5 mm diameter. Over time, this hole can be reduced by scale, meaning the block can overheat, causing a lot of steam from the exhaust.

This pipe can be removed by undoing the clamps, and by using a punch to remove it from the block, and either replaced by a new one, or cleaned up and reinstalled..... as long as it hasn't been damaged during removal. On refitting, the hole must be facing down.

Apologies for what might read as poorly explained. If you have a workshop manual it should have a better diagram and explanation.....

Many thanks - this is helpful. The pipe has been removed for inspection and scale deposits removed. As you say, the hole was quite small and has been drilled out to 6.5mm. We shall see if this has any effect.

 

[RJO]

To test the sail drive flow disconnect the hose, open the valve & see how much water flows through. You might also find the blockage is actually at the seacock so some work with a length of stiff wire whilst the water is gushing in may be worth a try. Check the filter is clean first of course.
Then get a large tub plus some buckets of water. Put the hose in that & top the tub up from buckets. see if the flow changes. You can compare flow rates, tub/saildrive
If you are happy that there is no difference between tub supply & saildrive supply I would look at the pump. Is the impeller OK? The cover plate may be worn & you could be loosing suction . See if it can be reversed. If so scrape the paint off & reverse it. That may well solve the issue. You can buy a new plate, or make your own . I can tell you how.
Of course you may still have to follow all the earlier posts about cleaning ports etc but my points are easily done & are outside the engine & easily undertaken first.

Thanks for taking the time to provide this advice - much appreciated. The access to the seacock is far from easy but, given the other things tried, I think that this is a good plan. I'll need to hold my nerve though with water gushing (or trickling?)in!

 

[Tranona]

The cock can be stiff, so operate it a few times before taking the hose off so you can be sure to be able to shut it off quickly when the water shoots in. No different really from taking a transducer out for cleaning.

 

[Spirit (of Glenans)]

Thanks for taking the time to provide this advice - much appreciated. The access to the seacock is far from easy but, given the other things tried, I think that this is a good plan. I'll need to hold my nerve though with water gushing (or trickling?)in!

Attach a short length of spare hose to bring it above the waterline.

 

[Spirit (of Glenans)]

To test the sail drive flow disconnect the hose, open the valve & see how much water flows through. You might also find the blockage is actually at the seacock so some work with a length of stiff wire whilst the water is gushing in may be worth a try. Check the filter is clean first of course.
Then get a large tub plus some buckets of water. Put the hose in that & top the tub up from buckets. see if the flow changes. You can compare flow rates, tub/saildrive
If you are happy that there is no difference between tub supply & saildrive supply I would look at the pump. Is the impeller OK? The cover plate may be worn & you could be loosing suction . See if it can be reversed. If so scrape the paint off & reverse it. That may well solve the issue. You can buy a plate, or make your own . I can tell you how.
Of course you may still have to follow all the earlier posts about cleaning ports etc but my points are easily done & are outside the engine & easily undertaken first.

To prevent the water gushing in attach a short length of spare hose to bring it above the waterline.

 

[Daydream believer]

To prevent the water gushing in attach a short length of spare hose to bring it above the waterline.

You may not need a spare hose . You would just disconnect the hose from the other end. That probably goes up to the filter & will be long enough & you could hold your thumb over it. . But still not such a good idea.
Then it will not gush in & you will have issues trying to get the hose below the water line properly to do the test
One actually wants it to gush in for a second or two to clear any obstruction. The few cupfulls one gets is nothing really. If one is worried then having a wooden bung, of a suitable size. handy , is all one needs to do. But turning off the stopcock will stop the water. If it does not do so fully then it will highlight that the stopcock needs attention at sometime in the future.

 

[RJO]

To prevent the water gushing in attach a short length of spare hose to bring it above the waterline.

Many thanks for this. You mention 'filter' - where do I find this?

 

[Daydream believer]

Normally the water comes from the saildrive up to a plastic bowl just about waterline level. This has a large lid about 80mm diameter which one unscrews. When removed there is a mesh disc. This is a filter that collects debris sucked in to the water intake. From here the hose goes to the raw water pump.
If one follows the hose from the saildrive upwards you should find the filter unit attached to a bulkhead somwhere. There are lots of different patterns.
It may be that you do not have one , in which case your raw water pump is drawing in weed etc & the impeller could become clogged or it could be passing the debris into the engine. I cannot imagine that . However, I do not know much about your installation so I may be totally wrong. Others may comment & correct me, so wait for further comment first.
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