Diesel & raw water cooling, what to look for

[Monterey]

I'm looking at picking up a project boat that is powered by a caterpillar diesel. It was originally cooled with a heat exchanger, but 2 years ago (but not too many hours ago) it went to raw salt water cooling due to a problem with the h/e. How much damage should I expect to find in that engine? Are engines ever designed for raw water cooling and if so, what is different about them vs. a fresh water/coolant engine?

Many thanks. I'm new to combustion-powered boats.

[kapnD]

Monterey, This will really be a major project if you intend to rebuild the engine. Two years exposure to salt water has most likely done irreperable damage to the block, heads, heat exchangers, aftercooler, oil coolers, everything in the cooling circuit. Its just a matter of time until it goes kerblooey! Dont let the "low hours" sales pitch lull you. If you put in a bid for this, assume that you will have to buy a new powerplant, even if it still runs. Yes, some engines are raw water cooled, but usually trailer boats that have a means of fresh water flushing at the end of the day. Modern diesels like to run at a design temperature, much better controlled through the use of heat exchangers.

[FAST FRED]

AN additional problem is that salt will fall out of solution at over 145F.

The Sea water in a Heat exchanger is always kept well under this temp so it won't plug up.

Your engine probably runs at 180F or more , so may be partally plugged with salt to add to the immense corrosion sea water cooling causes.

Plan on NEW EVERYTHING , or stay clear!

FAST FRED

[woodboat]

Salt as in "ocean" or some form of brackish? In the Chesapeake bay we have engines with twenty years that are still fine. If true salt then what has already been posted I agree.

[Monterey]

Thanks for your replies. To clarify, the engine is not modern by any standards. It's a 'very old' 4 cylinder naturally aspirated Caterpillar. It has been run in San Francisco Bay, and off the coast here, but if I buy it she will be kept in brackish water.

Now from a theorhetical design perspective, are there engines designed for SWC? If so, do they have internal differences (such as thicker castings, or different materials)?

I'm going down this saturday to re-examine the boat, and get the engine started, what should I be looking for, or listening for, to give me a sense of engine health?

Thanks again.

[D'ARTOIS]

Monterey,

In general, and to save the inside cooling channels of the particular engine one
uses normally inter-cooling systems. For a few reasons, direct cooling (raw water) is not advised. 1. Corrosion, 2. Temperature . There are some minor other reasons but protecting your engine against the corrosive salt water is an important issue. Secondly, with raw water cooling your engine will not reach it's designed operating temperature - 80/85 o Celsius.
About possible damage on the present engine: I do not think that there might be
already a considerbla amount of damage, although I had not seen the engine.
Take the waterpump off and look for yourself. Cat's engines are mostly of cast iron instead of a cast alloy of AlMg, so it might be ok.

[FAST FRED]

The only engine I can think of that was designed for sea water is the old Volvo MD series.

There were seperate cylinder & head engines , popular on small boats decades ago.

They had individual decompression levers and THEORETICALLY could be hand started.

But you had better have a really strong hand!!

Their secret to salt water ops was a cooling system with a 140deg thermostat.

Lousey for engine efficency , but cheap to build & maintain.

Poor construction and lousey parts selection doomed these engines,

The valve springs would snap if even a spot of rust got on them , and in a tower with the engine at only 140F there was LOADS of rust!
The Valve would drop into the running cylinder at repair HUGE cost .

Volvo's "solution" was not to purchase valve springs from the folks that made them for chevvy 6 cylinders (so rusty you could only wonder how they ever opened).

Volvos solution was to pretend there was NO problem , BUT they decided to simply dip the lousey springs in a plastic "tool grip" style solution, and change the part number!

Needless to say we never purchased engines from Volvo again.

FAST FRED

[kapnD]

In retrospect, I'd have to say that all modern diesels are designed to run on salt water...eventually! Heat exchangers, pumps, aftercoolers etc. are the achilles heel of the industry. If engines were designed to tolerate salty coolant, diesel mechanics would be sitting alongside the maytag repairman.

[kismet]

Hllo all
I am new to this site today, I have a 22 ft Falcon 22spc power cruiser, it has been retro fitted with a GMC V8 TURBO DIESEL made by Penninsular Its an old engine but gives me 38+ knots wiith a volvo duoprop stern drive.
Questions are these good engines if looked after

I do not see any salt water strainer or seacock are they pure fresh water cooled?

had loads of problems with the starter motor which is mounted under the exhaust manifold major grief to get at, can these be moved to on top.


Thats it chaps many thanks
Bruce