silly engine question

[briggsy]

Hi,
Im new to the world of marine engines.
I am considering to buy 2 second-hand ford 1.8 diesel engines.
Can I use the existing water pump to pump the seawater around the jacket to cool the engine.
I realise its more conventional to use a heat exchanger. I can understand this might be better for the prelonging the life of the engine but is there any real danger ?
I have seen this sea water system working in Thailand. I could afford to replace a £200 engine every couple of years. Why is it better to pay £1200 for each marinisation kit.
Please excuse my ignorance.

Thanks

 

[David2452]

Check out the Lancing marine site, will prove useful. You will be far better off using heat exchanger especially if you have the manifolds cooled as part of the closed system, sea water will corrode them and they will cost more than the engine to replace.


David

 

[burgundyben]

I think if your on a budget then its fine to do this, agreed it wont help the engine last a long time.

One thing to consider though, you might find it does not get up to temperature, water round here is between about 4 and 20 degrees through the year, engines are designed for closed loop cooling where on return from radiator or heat exchanger the water is still maybe 60 degrees, so engine may struggle to reach optimum temp which might be noisier and smokier etc, maybe also suffer from rings getting sticky.

 

[aztec]

raw water cooling for the budget reasons you have suggested is a good way to go.

Ben is right, there's two main problems.

the optimal engine temp and if you wanted one, a calorifier.

the water pump fitted is a centrifugal pump and as such will not prime (if it's above the waterline).. the right way to go is to make a fitting to replace this. this is where the water inlet needs to be from the "jabsco" type pump, this is driven from the v-belt. the engine temp can be controlled by the size of the inlet, but that's a bit trial and error.

you will have to make the exhaust too, it will need a water injection system unless you run a dry exhaust (i wouldn't), you could get an engineering/fabrication firm to make one.

i'm using two transit engines with this cooling ststem, and luckily enough the transit has a port above the connection to the downpipe that will take a stainless pipe to inject the used cooling water.

hope this helps, PM me if you need more info.

regards. steve.

 

[andyball]

The raw water circuit on my boat uses a centrifugal pump that won't prime on it's own.

If the strainer is above the pump ( like mine) ...I close the seacock, fill the strainer with water from a bucket - this fills the pipe down to the seacock & the one to the centrifugal pump. Top the strainer right up, put the cap back on, open the seacock - primed pump. There's an anti-syphon valve in the pump outlet line.


It was like this from the builders - it's no prob at all - you just remember to close the seacock before cleaning the strainer & open it again afterwards. Even if you forget - water for priming is not hard to come by on a boat.

 

[Talbot]

The thermostat will be interrupting the flow in order to try to maintain a working temperature. It is recommended that you use a thermostat that opens at a lower temp anyway, as this will reduce the amount of salt crystalisation.

 

[oldharry]

Several things to think about here:

Firstly, cooling the engine with raw seawater is perfectly Ok - unless it has an alloy cylinder head - which the Ford does not.

BUT: with any seawater cooled engine the average operating temperature should not exceed 60C. If it runs regualrly hotter than that, salt deposition takes place in the waterways, and a rock hard crystalline deposit builds up which is virtually impossible to remove, eventually blocking it.
It is not usually possible to use the existing cooling pump, for 2 reasons. 1, they often have alloy cast bodies which will rapidly dissolve in the presence of seawater and the steel of the block by electrolytic corrosion. 2. they cannot lift the seawater up to the engine unless the whole engine is below the waterline. Normally a Jabsco or similar type pump is arranged on a bracket near the front pulley, driven by a longer alternator belt, or more commonly a double pulley on the crankshaft allows the pump to be driven by its own belt The original pump is replaced by a plate, and the water inlet/outlets are arranged to suit.

The next problem is the exhaust manfold, which can get red hot in a boat, with a considerable fire risk. On the road the vehicle designer will have ensured adequate air flow over the manifold to stop it overheating. Similarly the exhaust pipe needs to be well insulated to prevent excess heat setting fire to the boat.

Normal practice is therefore to either use a combined heat exchanger and manifold, or a water cooled manifold. Almost always the hot water from the engine discharges into the exhaust pipe just after the manifold to cool the exhaust gases and exhaust pipe down avoiding the need for hefty insulation.

You will need to find some way round these excessive heat problems in your boat. If you can afford to 'replace the engine every couple of years' then you can well afford to set it up properly in the first place. If you blow the engine, the marinising parts can always be transferred to the new unit - particularly heat exhanger manifolds which are no more diffficult to fit than the standard car type.

Do the job properly to start with - you will regret it otherwise! You also do not want to risk a bad installation that will let you down. The law of the sea always ensures this happens at the worst possible and most embarrassing moment. Dont ask me why, but it is infallible! And more seriously could not only cost you your boat, but yur life!

 

[briggsy]

Harry . The main problem is that I can't afford the £2K+ cooling system for the engines. Maybe its not a lot to you and if I was planning to use nice shiny powerful engines to keep for years I would splash out. My proposed engines could be replaced every few years and cost about £50 and a free car. Why spend thousnds trying to protect them. Obviously the engines wil require a bit more inspection on a regular basis. If they look like their rusting too much, chuck i'm out and get another £50. I'll probably only do about 50 hours a year and can't see why my engine would disintgarete immediatley on touching a bit of salt. The salinity around here is dropping anyways
I now understand the problem with the pumps and I will have to pay up for the jabsco pumps. This is a 1 off purchase I will be able to use these probably forever. The exhaust I agree is the biggest concern I plan to modify the cast iron manifold to take water injection. Having not done it I don't know exactly I plan to talk to a engineering fabricator about it. However it appears that quite a few people are using home built systems. I posted the question to get advice. To assess feasability.
I plan to get my boat surveyed prior to its return to the water which should pick up any potential problems.

 

[oldharry]

Thats fair enough : I agree - you need not pay thousands for the conversions. All you need to do for a 'cheap and cheerful' conversion is to take the thermostat out altogether. The engine will then run over cooled, but that should not be too much of a problem on low useage. It would be worth doing something about a cooled manifold of some sort - which as long as you are using the same basic block can be switched from one to the next - the overheat hazard is a real problem with the manifold. As far as water cooling the exhaust is concerned, get an adapter made up which bolts on to the manifold outlet, with say a half inch pipe injecting into it, angled away from the manifold end about 45 degrees, then leading on to the exhaust pipe, which can be rubber diesel hose of suitable diameter. That then becomes a 'fit and forget' item, onto which you bolt replacment engines as you need them. The cooling water from the engine feeds into the exhaust, and hey presto! Its a good idea to angle the exhaust pipe down and away from the manifold, so that the water cannot run back into the valves: water in the pistons will mean instant terminal breakdown and new engine. ( if water gets in and the engine tries to compress it you bend or break the con rods - or even send the piston through the side of the engine!). Many ex truck engines run happily like this for years, and I had a BMC diesel set up this way which did just fine.

At 50 hours a year, you will find this sort of set up will last quite a few years before rust becomes a problem. Just dont be tempted to use an engine with an ally head! You would be hauling it out again within months because of corrosion!

I agree the cost of 'proper' marinisation is frightening, but try round the boat jumbles. The W\Sussex last weekend, I noticed someone selling heat exchangers etc for around 50 - 100 squids depending on engine.

A possible cheapo alternative pump would be to see if you can arrange a 12v electric pump of some sort? You need a minimum 1/2 inch bore and a reasonably good delivery rate - a good squirt, not just a dribble. But carry a spare! Electric pumps have a nasty habit of packing up at the wrong moment! The pump MUST be self priming - which is why the original circulating pumps are no good, and of course it must be seawater proof.

Compromise is never a very good idea at sea, because the sea does not compromise, and the stakes are rather high. But with a modicum of care, what you suggest sounds fine - as long as you can get round the fire risk probem of the exhaust manifold safely.

 

[muchy_]

A friend of mine had this setup in his Seamaster 28. He had that boat for 34 years with no problems at all. He sold it about 4 years ago and it is still going strong.

 

[briggsy]

Thanks Harry lots of info there to think on.
Like you say I may be able to get a heat exchanger cheap at a boat jumble.

 

[briggsy]

Thanks for that Harry.
Munchy , What did your friend do to cool the exhaust manifold ? Or did he just join a pipe at the end to cool the exhaust ?