PS Advisor: 04/01/03

Constricted Diesel Exhaust
I have been a subscriber since I was based in Washington DC from 1993 to 1998. Since returning to Melbourne I have kept up the subscription—with a US mail address. Your articles are still helpful here, particularly explanations and advice on what works and what is useful and practical.

On return to Melbourne I bought a Swanson 36. This is a modified fin-keeler sloop designed for our notorious Bass Strait—remember the Sydney-Hobart. It was launched in 1984. The engine is a Yanmar 3QM30(H), the raw water-cooled model. I do not believe it has ever been opened.

The engine has been overheating. There is a salt buildup in the cooling passages.  When I change the anodes I can get at some of it and remove it physically, but obviously there is more inside. It has been suggested that I remove the exhaust manifold and clean it out, but the installation is too tight and would require engine removal and I don't want to do this.

Is there any way to get rid of this salt buildup with solvents or some type of flushing? (I can't see how I could get hot water in quantity to the boat, but I can get a stream of fresh water to the engine with a hose in a bucket and engine raw water intake from the bucket.)

As a related supplementary question, the hot water is only luke warm and this is almost certainly the same problen of salt buildup. The exchanger is sealed and encased in insulation so I can't dismantle it. I could however remove it from the boat.  If whatever you recommend for cleaning the cooling system isn't 100% successful, would a hot-water flush be better for the hot water exchanger?

-Greg Scott
Melbourne Australia

As usual, if a diesel engine question is any trickier than can be answered by "give it clean fuel, fresh air, constant cooling water, and on-time oil changes," we referred it to Mike Muessel of Oldport Marine in Newport, RI. Here's his response:

"The 3QM30 is a robust and long-lasting engine. We used them in our commercial launches for many years and were able to get 12,000 and more hours out of them between overhauls.

"The engine was made in two-forms, salt and freshwater cooled. Both were excellent, but as you have found, the raw water-cooled engines were subject to salt and rust build-up after many years of use. Yanmar built the raw water-cooled ones with a lower-temperature thermostat to reduce salt buildup, and that prevents them from being efficient domestic hot water suppliers.

"Your engine can probably be fixed, but unfortunately it involves that dreaded job of removal in order to replace the exhaust manifold, which is undoubtedly plugged with a mixture of salt and rust. The good news is the manifolds are still available, and it's high time to replace the mounts, change the exhaust elbow, check the external oil lines for corrosion, service the throttle/shutdown assembly, and paint the engine. Bite the bullet and do the job right the first time.

"There are new salt-removal products on the market, but I doubt they will dissolve the rust that is built up in your cooling passages. That mission can be accomplished with a dilute mixture of muriatic acid. Read and heed the caution label, wear full protection, including hands, eyes, nasal passages, and body, and don't spill it on anything you don’t want ruined!"

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Don't Thin Lube Oil
I have a 1982 Ford-Lehman 4D220 engine with 3,600 hours of use. The oil pressure, which used to be, more or less, at 40psi., has steadily declined, over the years, to 25psi. +/-. I changed the sender and gauge, but saw no improvement. Although, the engine runs fine, some friends have told me to run it up to temperature, siphon off half the oil, replace it w/ diesel, run it for 5-10 minutes, and immediately drain the lot. This, supposedly, will clean out all surfaces, strainers, orifices, etc., and most certainly get my oil pressure back up. Although it sounds like a good idea, I'm a believer in the old axiom "if it ain’t broke, don't fix it."

I would very much appreciate your comments on this, as I'm presently preparing to replace my front shaft seal.

-Frank Vital
Via e-mail

Blast, that didn't fit our "Diesel 101" expertise framework, either, so we went back to Mike Muessel:

"You have mostly answered your own question, and I agree with your answer of 'if it ain't broke, don't fix it'. Your engine is far from broken, and flushing it with a dilute mixture of diesel fuel and oil won't gain you anything.

"Oil pressure in an engine is a measure of the resistance of the oil being pumped through the small spaces between the crankshaft, the camshaft, and the rocker shaft, and their respective bearings. These spaces get larger as the engine wears, and thus more oil flows through them, but at a lower pressure—and that's not necessarily all that bad.

"'Cleaning' the inside of the engine will not decrease these spaces, but it may very well have just the opposite effect when all the particles that were once solidly attached to the inside of your engine are sent through these very critical passages in an ineffective lubricant mixture.

"Your modern detergent lube oil has been working very hard over the years to carry those small particles and contaminants to the oil filter, where they were efficiently removed. The ones that have not been sent to the filter are solidly stuck to the inside of the engine, where they will happily stay until you decide to overhaul the engine. At the rate you are racking up the hours, and given the Ford's track record, that should be in about in the year of 2043. If you still have the boat then, let me know how you made out."

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In-Mast vs. In-Boom
I'm a new subscriber and as such have not seen all the articles you've done.Have you ever done a comparison of in-mast vs. in-boom mainsail roller furling systems, showing pros and cons of each, including performance differences, if any? I see that you did an article in Oct. 2001 on in-boom furling systems, but I saw no comparisons between the two systems. I would be interested to know if one stood out over the other in terms of handling, performance, etc.

-Ron Oxford
Via E-mail

We haven't done a direct comparison of in-boom vs. in-mast furling systems, but we think the in-boom systems are preferable, especially for regular-sized cruising boats. They're easier to install, easier to manage, and less expensive (although mechanically they're not really simpler than in-mast systems). In-mast systems require an awful sacrifice of mainsail shape—you end up with a battenless, hollow roach—whereas with an in-boom system you can have a pretty normal sail. Before buying either system, try sailing a boat with simple, carefully installed slab-reefing.

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