Dealing with a rusty raw water cooled engine

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seaangler23

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My boat runs an old petter which is likely 40yrs old, still runs great but having some issues with water flow through the engine which is raw water cooled.
The engine had no anodes in it, they don't make them any more and I have no idea how long it had gone without.
I am planning to make some but as with everything it's on the to do list.
I pulled the plate off the top of the water cooled exhaust manifold and it's not pretty. Is there somewhere who will clean it up and is there any type if coating suitable to cote the water ways? I could get at some of it with my needle gun but afraid of cracking it.
I know engine blocks can be acid dipped but no idea if this is even to far gone for that. Unfortunately spares are few and far between for it so have to make do.
 
Soak it in brick cleaner HCA will clean all the rust and once clean pressure test it for leaks. If it leaks it could be welded or sealed with penetrating epoxy to seal any porosity.

My exhaust manifold is fabricated stainless steel and yours could also be fabricated by a good engineering workshop.
 
Il try the brick cleaner thanks, if I can il try find one that's been used in fresh water and get the manifold and blocks off it but il need to make so with what I have for just now.
 
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That is certainly not a pretty sight

Hydrochloric acid may well clean it up but Id be afraid of overdoing it and ending up with a load of leaks

BTW not all brick cleaners are hydrochloric acid based. you will have to consult the labelling or the safety documentation to be sure.

I think if the engine was originally fitted with anodes I would move making some new ones up the list of priorities. Remember though any old zinc will not do. Get some bar of the correct specification or you will be wasting your time and effort.
 
Cheers, I've been avoiding it but I think a full strip down of the blocks will be needed over winter, the original anodes were part of a gasket on the lower water manifold , not straight forward to remake or replace, so looking at braising on threaded lugs and using Volvo type ones that thread in. We Have avoided opening the engine up as I was aware of the potential problems and as the damage was done I was just going to run it until something let go,
 
Not too sure about putting in a load of acid. Personally I would get as much rust out as possible - using mechanical means including those flexible "curtain wire" type drain unblockers and see if that does the trick.
If it works then perhaps stabilise the rust with KU rust and hammerite ( hammerite haters please dont shout) and fit anodes
If it does not work then try the acid but make sure it gets a good rinse out.
 
I have a Centaur with the original VP MD2B, I believe it had suffered for some time with a worsening reduced water flow problem.

A previous owner had removed the thermostat, it had a new water pump fitted that helped but the volume of water was still not what you would expect, and pushing against a tide the engine would start to over heat at higher revs.

Over the winter I went for a kill of cure apporach, I filled a bucket with sulphamic acid http://www.ebay.co.uk/itm/Sulphamic-Acid-99-5-Pure-5Kg-/141696033149 and connected the raw water intake and exhaust to the bucket.

I let it run for an hour, before flushing for another hour.

It worked for me, I have fitted a new thermostat and for the time being at least I have no cooling issues.

But I guess it could just as easily killed it.
 
GaryCottam said:
I have a Centaur with the original VP MD2B, I believe it had suffered for some time with a worsening reduced water flow problem.

A previous owner had removed the thermostat, it had a new water pump fitted that helped but the volume of water was still not what you would expect, and pushing against a tide the engine would start to over heat at higher revs.

Over the winter I went for a kill of cure apporach, I filled a bucket with sulphamic acid http://www.ebay.co.uk/itm/Sulphamic-Acid-99-5-Pure-5Kg-/141696033149 and connected the raw water intake and exhaust to the bucket.

I let it run for an hour, before flushing for another hour.

It worked for me, I have fitted a new thermostat and for the time being at least I have no cooling issues.

But I guess it could just as easily killed it.
Click to expand...

One of the the troubles with those old two cylinder engines it that the smallish passages in the exhaust manifold that carry the cooling water to the heads become blocked. One is longer than the other and is likely to be more severely restricted. This can lead to a situation where one cylinder is overheating while the other is being over cooled to produce the correct average by the thermostat and displayed by the temperature gauge.

If I were you I would at least feel the two blocks and cylinder heads to make sure one half of the engine is not much hotter that the other. Preferably get a contact or infra red thermometer so that you can check more accurately.
 
also these petter av engines have a tiny pump and the water flow isnt great when they are working properly. the exhaust can get rusty from the manifold and this restricts flow too. they dont pump water out of the exhaust like modern engines
 
Il be taking the exhaust manifold off and trying it, I think it will be the cure or kill approach as I'm for the do it once and do it properly train of thought so I can have confidence in it. I'm checking canal boat forums for some bits, my thinking is they have been run in fresh water so likely to be in a lot better condition, but again it's a long shot.
She seems to pump water ok but sure it's worsening, I removed the thermostat as it looks like it has been causing more issues as its jammed shut.
I keep an infra red thermometer on board and keep track of the temps on each cylinder, they keep about the same
Just going to do what I can for the season then attack it and hope she holds together!
 
Last edited:
Eventually pulled the manifold off and the head of the engine, there is a lot if crustyness. The manifold actually is ment to have clearance of around 5mm down each side of the exhaust casting and the water jacket, how it didn't overheat I don't know. After a few attempts of power washing, needle gunning and attacking it with a flat screwdriver a lot of debris and rust was removed, there won't be much more I can do with tools so I'm going to try dipping it in brick cleaner then going to look at the possibility of coating the water ways with some sort of paint, il need to research this as I don't want something that will come off and block up the waterways.
 
I would stop there. You have got the thick of the crud off, attacking it with any acid isn't going to make any significant difference and could easily turn it into a collander.

A good poke in all the other waterways would help though. Maybe use a chemical treatment on bits you can't reach with poky implements.
 
To be honest I think the abuse I have put it through if it was going to break, it would of by now, acid won't eat through more than the surface of what's there and from what I can see it is a thick casting with areas under the exhaust casing I can't get to so il give it a try. It's down to kill or cure it as I'd rather be happy it was as clean and treated the best it can be rather than leaving something half done which will bite me later
 
So I have had a go with hca, I used jewsons brick and mortar cleaner which is 15% hca they do a brick and patio cleaner which is 10%.
I tried it for a few short periods then went and left it over night , I retuned to some nasty looking foam overflowing the tub, it has done a great job, cleaned up what I has done and got stuff out I couldn't reach. One word of warning is wear a mask, I was using a face mask, chemical gloves but when I opened the shed in the morning I got a tingly tounge off the fumes


 
I'd like to coat the waterways in some sort of protection, but something that won't come off, especially with this being the last part to see cooling water once or starts I don't want something that will burn off and cause a blockage in the injection elbow
 
I would be reluctant to put any form of coating on. It is virtually impossible to apply any coating that is 100% impervious to water, with the result that corrosion gets underneath and the coating flakes off. For example, my keel had five coats of West epoxy followed by four of Coppercoat but rust was coming through within a year. In your situation I would make sure you fit anodes, modifying others if they are not available for your engine.
 
Your probably right I just hate going to this effort to leave it exposed but it's lasted 40 years this way so must have life left yet, now how to tackle the heads and water jackets....
 
It would be well worth trying to fit a corrosion protection anode in the waterways of your motor. The lime scale is a different problem that the HCL has addressed (I used Fernox DS3, which contains Sulphamic acid, with good results on my Bukh DV20).
DV20's left without anodes tend to get corrosion at the bottom of the cylinder liners and thus leak around the O ring seal that stops the water leaking into the sump
 
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