MD2030 overheating and empty strainer. Surely there must be a simple fix!

[Robatbradwell]

I have an intermittent overheating problem on my Legend 33 with a Volvo Penta MD 2030. It will run just fine for ever at all speeds but when cutting the engine and sailing for a few hours it overheats shortly after start up and, of course, just when you don’t want it to! The raw cooling water stops flowing out of the exhaust.

I have checked the impellor, looked for blockages at the heat exchanger, all the usual stuff. I did find 4 broken impellor blades blocking the heat exchanger but have now removed them and still have the overheating problem.

I now think that my problem must be an air leak or faulty anti siphon loop valve (if that is what it is!!). The strainer is always empty when I check it and on start up from cold it takes ages for the water to start appearing out of the exhaust. The manual says this should not be more than 30 seconds but it must be more like 3 minutes.

I can temporarily fix the problem by shutting off the inlet sea cock (on top of the sail drive) and then filling the strainer up with bottled water, closing the lid tightly before opening the sea cock again. Water then stays in the system and flows through the exhaust just fine.

None of the pipes seem to be leaking and I have checked the strainer for air tightness.

My strainer is above the waterline and I have what looks like an anti siphon loop. I have checked the loop valve bend and I can blow air into it but cannot suck. It seems to me that this would let air in to the system. Might this be faulty and it should only let air out? Surely then it wont be anti siphon but letting air in can’t help keeping the system primed!

Surely there must be something simple that I am missing!

Any help much appreciated.

 

[oldsaltoz]

It sounds like air getting into the system for sure, problem is going to be finding the leak,

First check the filter lid seal and any loops siphons in the system.

You could run a temporary bypass hose direct to the pump to eliminate the stainer leak theory, if this fixes the problem you know what area the leak is in.

Last resorts could be pump seals or hoses between inlet valve and pump.

Good luck.

 

[penfold]

Your anti-syphon is working as it is supposed to; you don't make it clear where it is, but the anti-syphon valve should be mounted between the saltwater outlet and the exhaust water injection elbow. It sounds like the gasket on the strainer could bad, but that's a side issue. I would suspect that either the saltwater pump has a problem(bad impeller, running the wrong way, worn housing), or there's a blockage or restriction in/around the seacock. Is there an internal or external strainer on the seacock?

 

[Robatbradwell]

Oldsaltoz, i have checked the pipes and strainer lid and all seem good but i will check again. A bypass of the strainer may fix the problem but it would be difficault to monitor water loss if i cant see into the strainer!

Penfold, I dont understand why one would want to allow air in via an anti-syphon loop! The set up is raw water supply pipe up to strainer, strainer down to pump, pump up to anti-sypon loop at same height as strainer, anti-syphon loop down to heat exchanger inlet, heat exchanger outlet to exhaust inlet elbow. I have changed the impellor twice and am sure it is fine. When the sustem is primed the water runs out well and is not too hot.

 

[colvic987]

you mentioned you have changed the impellor twice, is the cover back on with a new gasket, i changed mine a couple of years ago and had a problem with the cover letting air in, this was sorted by putting grease on both sides of the the paper gasket then fitting it.

If this is not the problem and you say the strainer is fine, then i would be looking at the places where the pipes are jubilleed up, as you could have a split or loose pipe which could be letting air in.

 

[colvic987]

I have an intermittent overheating problem on my Legend 33 with a Volvo Penta MD 2030. It will run just fine for ever at all speeds but when cutting the engine and sailing for a few hours it overheats shortly after start up and, of course, just when you don’t want it to! The raw cooling water stops flowing out of the exhaust.

I have checked the impellor, looked for blockages at the heat exchanger, all the usual stuff. I did find 4 broken impellor blades blocking the heat exchanger but have now removed them and still have the overheating problem.

I now think that my problem must be an air leak or faulty anti siphon loop valve (if that is what it is!!). The strainer is always empty when I check it and on start up from cold it takes ages for the water to start appearing out of the exhaust. The manual says this should not be more than 30 seconds but it must be more like 3 minutes.

I can temporarily fix the problem by shutting off the inlet sea cock (on top of the sail drive) and then filling the strainer up with bottled water, closing the lid tightly before opening the sea cock again. Water then stays in the system and flows through the exhaust just fine.

None of the pipes seem to be leaking and I have checked the strainer for air tightness.

My strainer is above the waterline and I have what looks like an anti siphon loop. I have checked the loop valve bend and I can blow air into it but cannot suck. It seems to me that this would let air in to the system. Might this be faulty and it should only let air out? Surely then it wont be anti siphon but letting air in can’t help keeping the system primed!

Surely there must be something simple that I am missing!

Any help much appreciated.

The anti syphon Should only let air in, thats how it works, you have a automatic valve version, as long as the valve is letting the air in when you blow on it, it moves and doesnt allow air out then its ok.


When the system is full of water the pressure of the water closes the valve when the engine stops the valve allows air into the valve breaking the syphon effect and stopping your engine filling with water and flooding the boat.

The other type allows a consistent flow of water out of the valve whilst the engine is on, and sucks air in when it stops.

 

[gavin_lacey]

From the fact that the system runs properly when you prime it, it is clear that the water loss over time is problem. Do you have the black volvo strainer? The seal on this strainer is created by an inner plate that seals on a rubber gasket on top of the white sieve. When you unscrew the top you should have to pull quite hard on the inner plate to break the airlock. If you do this without closing the seacock you will have to re-prime the system in the manner you describe as you will when you dismantle the pump. If the inner plate is not sealing or is missing then the water level will drop. Although the system will self prime in theory, as you have found it can take a long time during which time damage can occur.

 

[ianat182]

My guess is that the inlet seacock is blocked with the usual barnacles, baby mussels and weed, perhaps even a plastic bag. Try detaching the pipe leading from the strainer to the inlet seacock and rod it through using some curtain wire; even this may not clear it if there is a strainer on the outside of the hull as they grow inside the grid,if you haven't scrubbed off in recent months this would be my first check.
I bought a pump from Lidls for £2.99 as a cheap solution to clear cockpit drains and raw water pipes, used it once so far this season.

ianat182

 

[Bosun Higgs]

I had the symptoms you describe on a Yanmar 2GM, and the problem was that the raw water pump was worn. Not always easy to see since the wear is on backplate as well as face plate and the little brass hump that bends the vanes. But as a result the raw water circuit used to empty out when the engine was stopped and took ages to re-prime itself. The short term get around was to open the raw water filter and re-prime the pump from a container of water then immediately start the engine.

The long term cure was a new pump, though I had the old one re-furbed as a spare.

 

[Tranona]

Two most likely culprits have been identified. First is poor seal on the strainer - either the screw top, the hose connections or a crack in the top. By pass the filter by connecting the intake hose direct to the pump. If it picks up water quickly then replace the strainer, hoses and clips. If not then it is almost certainly a worn water pump face plate. Replace with a Speedseal (which is a sensible thing anyway) or a standard face plate if you don't mind dealing with 6 tiny screws and a paper gasket every time you change the impeller.

 

[MINGUS]

we had similar case and found that the problem was situated in the exhaust riser. It was rusted inside. After cleaning the inside we noticed that the side was leak.
Double trouble, so we replaced it and the engine works properly.

 

[Robatbradwell]

Colvic987, cheers, i shall follow your advice. I had a new gasket but fitted the old one as it seemed to fit better and was in good condition, but i should have replaced it and i do have some gasket sealer to add. I will also check the srainer and pipes again.
The mechanics of the anti-syphon loop were getting fuddled in my small brain but i think that i now understand that it can let air in to the exhast side as it is down hill and this water will such in the air as opposed to syphoing through from the sea cock, and it wont allow air back to the supply side cos the strainer is possitioned at the same height, thus no suction from water falling back, as long as there is not a frigging air leak!!!

Gavin, it is a see through plastic strainer with a screw lid and rubber O ring seal. It seems to be in good order and airtight but i will check it yet again. A worn pump is interesting but the engine is a 2004 and has only done 300 hrs. I will inspect it carefully and try to test your theory by blowing through the inlet whilst holding my thumb over the outlet.

Ian, the seacock is not blocked. I have alredy checked this out. My problem is intermittant and due to air in the system. So thanks for nothing but i still love you.

Bosun, i shall check the pump for wear but if there was wear wouldnt this just make the pump perform poorly. I dont understand how wear on the front and back plate would allow air in!

Tarona, good advice, i shall try to issolate this problem by bypassing the strainer and check the pick up time. A speedseal face plate is a good idea so will do that. I shall try to get this from Keepart. But i am guessing that it is a leak on the gasket as opposed to wear on the face of the plate!

Cheers, you are all Legends!

 

[Robatbradwell]

Mingus, if i had a leak in the exhast would it allow water to drain away from the strainer side when i have an anti-syphon loop that is possitioned above the exhaust? I am struggling to get my head around this one!
But i must say that when i took the rubber pipe off the CI exhast inlet there did seem to be a bit of crud, possible corrosion, down in the inlet.

 

[penfold]

Oldsaltoz, i have checked the pipes and strainer lid and all seem good but i will check again. A bypass of the strainer may fix the problem but it would be difficault to monitor water loss if i cant see into the strainer!

Penfold, I dont understand why one would want to allow air in via an anti-syphon loop! The set up is raw water supply pipe up to strainer, strainer down to pump, pump up to anti-sypon loop at same height as strainer, anti-syphon loop down to heat exchanger inlet, heat exchanger outlet to exhaust inlet elbow. I have changed the impellor twice and am sure it is fine. When the sustem is primed the water runs out well and is not too hot.

Your anti-syphon is in the wrong place, but I'm fairly sure that isn't causing the problem. It should be mounted as shown in this diagram between intercooler outlet and exhaust water injection elbow, so it's at about the waterline when heeled(assuming it's offset to one side). It's purpose is as suggested by its name, it stops water syphoning into the exhaust, filling it up and banjoing the engine. It lets in air when the engine stops, breaking the potential syphon.

Where is the water pump relative to the water line? If it is above the waterline, it will have to work quite hard and needs to be in good nick. Where is the strainer relative to the intercooler? Some engine makers recommend mounting level with the waterline, but if the water pump is close to or above that the strainer should ideally(IMO) be mounted with its bottom level with the top of the intercooler(with the caveat that the anti-syphon should be level with it or slightly above) in order to maintain the prime. Sometimes internal layouts don't allow this, but this would minimise the chance of your problem repeating.

 

[Robatbradwell]

Yes, Penfold, according to that diagram my AS loop is on the wrong side of the intercooler (assuming this is what i thought was the heat exchanger!). My punp is low so must about same as waterline or below and the strainer is possitioned as you say it should be with the bottom of it level with the top of the intercooler. The AS loop is just a little bit above the strainer.
When back on the boat this weekend i shall hunt down the problem armed with all this helpfull information. I now have my money on it being the impellor cover gasket!

 

[neil_s]

You might find that your pump is a bit worn, as several have suggested. On my DV20, this means that a new impeller is required at more frequent intervals to ensure that the pump will self-prime. If it takes such a long time to prime the system through, remember that your pump is running dry, too. Wear will be accelerated. Could you reduce the length of the water inlet piping - and perhaps reduce its diameter to help the pump a bit?

neil

 

[penfold]

Intercooler=heat exchanger. Two words for the same thing. Something else to do/check; inspect the strainer body and lid where the o-ring seats for moulding flash(fiddly bits of extra plastic which are left after the bit was made) or other imperfections. If there is any flash trim it off with a sharp knife or chisel. Also smear the o-ring with vaseline or silicone grease to ensure a good seal. Maybe even get a new o-ring as they do go hard and stop working so well even when they look ok.

 

[Robatbradwell]

Thanks neil and Penfold.

I have noted that on later model of my boat they have moved the srtainer to the front under the galley steps and thus closer to the sea cock on the saildrive. This will greatly shorten the inlet hose to the strainer and make it much easier to get to, so i shall try to do this as well as everything else you have suggested. Cheers.

 

[Marsupial]

Clearly the shaft on your water pump is worn, and the seals (they look like oil seals) are now running in a little furrow of wear in the steel shaft and are letting air in. The new impellor has improved the pump but its easier to pump air than it is water so it pumps air through the seals.

The remedy is to buy a pump overhaul kit OR a new pump.

 

[Robatbradwell]

Good point but do u think that likely on a 2004 engine with 300 hours?