How to maintain
and repair
a boat engine.
         Contact me.

This page updated: March 2013

General section
Maintenance section
Diagnosis section
Repair section


Sailnet - Tom Wood's "Drive Train Vibration"
"Drive Train Tune-Up" article by Harry Swieca in issue 2002 #1 of DIY Boat Owner magazine
"Diesel Engine Electrics" article by Don Casey in Mar 2002 issue of Blue Water Sailing magazine
BoatDiesel - Tony Athens' "Engine Life"
BoatDiesel - Ian Hodgkinson's "How to Beat the Detroit Overheat Blues" (acid flush of cooling system)
Sound Marine's "Some Common Questions" (about diesel engines)
New to Diesel Engines ?

The Boat Doctor


David Pascoe's "Diesel Maintenance Or Lack Thereof"
Engine maintenance article "The Three Hour Oil Change" by Don Casey in 10/2000 issue of Blue Water Sailing magazine.
Don Casey's "Changing Engine Oil"

Mostly from "Good Boatkeeping" by Zora and David Aiken (on Amazon - paid link):

From David Pascoe's "Diesel Maintenance Or Lack Thereof":

Changing oil:

There could be oil and dipsticks for:

Possible fuel filter locations:
Your boat may have more fuel filters than you suspect; don't overlook:
If your engine has a cartridge-type fuel filter, you may be able to buy an adapter (such as from ABC Precision Machining) to make it take a spin-on filter (better).

Possible oil filter locations:
Your boat may have more oil filters than you suspect; don't overlook:

Possible air filter locations:
Your boat may have more air filters and screens than you suspect; don't overlook:

Valve clearances:
Adjusting the valve clearances (maybe every 2 years or so) can improve performance ?

From John Dunsmoor:
> I'm thinking of measuring/adjusting my valve clearances.
> Simple procedure specified in manual, but I have to
> rotate the engine to different crankshaft positions.
> There is nowhere to put a big wrench on the flywheel
> or anything. Won't cranking the engine with valve-cover
> open spew oil everywhere ? How can I do this ?

Should not spew oil, not just bumping the starter. Oil is pumped through the rocker arm shaft, then drains back into the crankcase. So there is no real squirting per se. Not to say that you can't get a mess going if you have the valve cover off. I have actually adjusted the valve on an engine while it is hot and running. With solid lifters you can do a pretty good job just listening to the clicking of the lifters. You do not want to overtighten, you will burn a valve if they do not close all the way. And with a diesel, it is running so slow, a little loose is not much of a problem either.

From Gary Elder:
Throw decompression lever [or loosen all injectors], so you can rotate the engine by hand.


Troubleshooting via exhaust:

BoatDiesel - Tony Athens' "What is white smoke?"

Smoke at startup is normal; cold engine can't burn fuel completely.

Engine won't turn over,
mostly from "When Your Engine Won't Crank" article by Harry Swieca in 6/2000 issue of Sail magazine, some from "Servicing the Starter Motor" by Roger Hellyar-Brook:
  1. Shift lever in neutral ? Neutral safety switch bad ? Try moving gearshift lever back and forth.
  2. Breakers and battery switch set correctly ? Ignition switch correct ?
  3. Battery voltage okay ?
  4. Inspect battery terminals; clean and tighten.
  5. Check all big wire connections, especially ground connection. Look for any loose wires of any size.
  6. Check large fuse in starting ciruit.
  7. Label, remove, clean and re-attach wires on starter solenoid.
  8. Check voltages at starter solenoid:
    • Large red wire should have battery voltage,
    • Trip-wire S terminal (connected to ignition) should have zero or battery voltage depending on ignition switch position.
  9. Check voltage at starter solenoid while cranking.
  10. Turn battery switch off and tap sides of solenoid and side and end of starter motor lightly with hammer. Then try to crank engine.
  11. Turn battery switch on, and repeat tapping while someone else turns ignition key on and off rapidly. Then try to crank engine.
  12. Make sure engine will turn over physically: put a wrench on the crankshaft end and see it you can rotate it.
  13. If engine won't rotate at all, remove injectors, crank engine, and see if water comes out of any cylinders.
  14. Remove the starter, check to see if teeth look mangled, and oil its gearing (where it engages the flywheel) a little.

Starter solenoid does two things: acts as relay (activated by low current from ignition switch) to send high current from battery into starter, and pushes gear up starter's shaft to engage flywheel.

If no click when ignition switch is turned, ignition switch circuit is bad or solenoid is stuck or failed. If one solid click but no cranking, solenoid probably is okay, but current is weak or starter is bad or engine is seized.

If rapid clicking when ignition switch is turned, there is insufficient voltage at the starter (low battery or bad connection).

From The Marine Doctor's Forum:
If your starter does not work, follow these steps:
  1. Check the terminal of the starter motor. If there is 12 volts, the starter is faulty.

  2. Check the small terminal of the starter solenoid/relay. 12 volts indicates the following possibilities:
    • A faulty starter solenoid/relay.
    • Starter relay not grounded.
    • A faulty lead wire from the solenoid/relay to the starter.

  3. Test the neutral safety switch (output side). 12 volts here indicates:
    • A faulty lead wire from the neutral safety switch.

  4. Check the input side of the neutral safety switch. 12 volts here indicates:
    • Gearshift not in neutral.
    • Neutral safety switch not adjusted properly.
    • A faulty neutral safety switch.

  5. Check the S (Starter) terminal on the ignition switch. 12 volts here indicates:
    • Faulty wire in the harness.

  6. Test the B (Battery) terminal on the ignition switch. 12 volts here indicates:
    • Faulty ignition switch.
    NO voltage here indicates:
    • An open circuit from the Battery.
    Less than 12 volts indicates:
    • A poor connection or a short or your battery is low or dead.

My experience with my starter motor 2/2011:

Hard to start:

Summarized from "Keeping It Cool" by Don Casey in 1/2001 issue of Blue Water Sailing magazine:

From Thomas Theisen on SailNet's Gulfstar mailing list:
... We could run at about 1700 RPMs but anything over that and we would overheat. We cleaned the heat exchanger several times and replaced and checked the thermostat. Finally, we went through the hoses, every rubber hose between the seacock and the exhaust manifold. We found that several had cracks and wear that were actually slowing the water flow. We replaced every rubber hose and this has solved our problem.

From Brian Armstrong on SailNet's Gulfstar mailing list:
... had overheating problems. My solution was to put about a pint of "lime-away" in the fresh water cooling system and run the engine for an hour or so. The temperature gage came right down to normal after about fifteen minutes. After a very thorough flushing the cooling system was as good as new. I have not had any temperature problems for the last two years.

Running too cold:

Sluggish / loss of power / stalling:

Engine quits while running:

RPM surges up and down:

Won't go over certain RPM (but no black smoke / overloading):

Too loud:

Excessive vibration:

"What's Making Your Engine Vibrate?" article by Harry Swieca in 9/2001 issue of Sail magazine

Rising oil level:

Bad-looking oil:

Water in oil:
To fix:
  1. Look for water in cylinders. If so:
    1. Remove fuel injectors.
    2. Pump/sponge water out of cylinders.
    3. Turn engine over briefly (by hand if possible).
    4. Repeat previous two steps until no more water.
    5. Pour diesel into the cylinders.
    6. Turn engine over briefly (by hand if possible).
  2. Fix the leak.
  3. Change oil:
    1. Change oil and filter.
    2. Run engine for 15 minutes.
    3. Repeat previous two steps until oil is okay.
  4. Run engine up to normal temperature and then run it for 30 minutes there.

Fuel leak into oil system:

Don't run engine with much diesel in the oil; it thins the oil a lot and can damage the bearings.

Loss of oil pressure:

Oil leak from bell housing between engine and transmission: probably means oil leak from the main bearing seal where the drive shaft comes out of the engine. Not supposed to be any oil inside the bell housing (on a Perkins diesel).

Black gunk in primary fuel filter (summarized from "Feeding the Beast" by Don Casey in Nov/Dec 2000 issue of Blue Water Sailing magazine):
  1. If it smells like varnish, you have old "flat" fuel: discard the fuel.
  2. If a couple of drops of bleach turn it white, you have algae: treat the fuel and then clean everything.
  3. If it dissolves in WD-40, you have tar: use the fuel until nearly empty before refueling.

From article by Steve D'Antonio in 11/2001 issue of Cruising World magazine:
Diagnosing fuel contamination:

From "Oil Test" article by Larry Blais in issue 2003 #3 of DIY Boat Owner magazine:
Reading results of engine oil analysis:
Also can test coolant, hydraulic fluid, transmission fluid.

From Al Herrle on SailNet's Gulfstar mailing list:
I have a Perkins 6-354 with compression at 320 psi, 420, 415, 270, 380, and 400 for cylinders one thru six respectively. The mechanic suggests that a valve job be conducted at a cost of approximately $1500. If that fails to address the compression problem, they further recommend removing the block and repairing as necessary. They suggested that the cost of this venture could exceed $15,000.
From Roland Storbeck on SailNet's Gulfstar mailing list:
The compression problem is going to be either the valves or blow-by at the rings. Try this: squirt a little lube oil into each cylinder (I find that 80 weight gear oil works the best). Repeat the compression test. The oil will substantially help seal the rings, so if your compression improves a lot then your problem is the expensive rebuild. If the compression only improves a little, then you're looking at the valve job.

On underside of coolant filler cap, slimy white paste or very dark coolant: exhaust gasses are getting into the cooling system.


Jim Kerr's "Fuel Injector Cleaning"

Injection pump service / injector service:
Blue Ridge Diesel Injection
Foley Marine (a pain to work with)
Fred Holmes Fuel Injection (Canada)
J & H Diesel Service
Jobbersinc (best pump price I found)
Real Diesel (888-349-9461)
US Diesel

When sending injectors out to be serviced, do not send washers with injectors. My injectors came back without the washers, and I had a difficult time getting new washers.

From Gordon Endler, and consensus of others:
[When replacing fuel injection pump on my Perkins 6.354, I asked if getting the timing wrong could damage the engine, injectors, fuel lines or injector pump.]

If your pump timing is out it will not damage your engine. Depending on how far it is out, it will either not start at all, or if just out the engine will have no power and be hard to start. Might smoke as well, but you can not damage the engine; it is only if you get the valve timing out that you can damage the engine.

Fuel line thread sealants: Rectorseal #5; Whitlam TU-555 Thread Sealing Compound.

Gunk/growth in fuel tank:
Summarized from Steve Wolfe in 4/2005 issue of Sail magazine:
Algae doesn't grow in diesel; bacteria, fungi and yeast can grow in the water in the tank and tolerate diesel. Some eat the hydrocarbons in diesel and produce sludge. Others eat the sulfur in the fuel. Keeping water out of the tank will prevent most growth. Magnets don't work to destroy growth; if they did, every sewage plant in the world would use them.

From TTollef552 on the Morgan mailing list:
I had a similar problem in the Bahamas far from tank cleaning services. What I did was remove the tank access lid, use the dinghy hand-pump to draw the fuel off the tank bottom where the microbes exist and into a bucket. When the bucket was full, I would pump the fuel back into the tank through clean rags and shop towels. We did this pumping for three hours on each 35 gallon fuel tank. Then I would change out the Racor filter element. The engine mounted spin-on filter did not need change-out every time as the Racor primary blocked most of the grit. I would recommend a supply of a dozen fuel filter elements of each type on board until the contamination problem cleans up. And lots of toweling in your engine supply stores.

An amazing number of black grit (dead critters ?) were captured by the improvised rag filters. This method worked, cleaning up the fuel adequately; the filter blockage went from every three hours to twenty-five hours. Filter changes were necessary all the way home. Now the interval is back to a hundred hours after tank cleaning by fuel extraction, filtration, tank scouring under fuel pressure and scraping behind the fuel baffles. The latter scouring behind the baffles was very important; fuel cleaning services usually avoid this time-consuming effort. You should also change out the fuel tank access lid gasket (hardware store item) before you close up the tank.

Water in fuel tank:
From John / Truelove on the IRBS live-aboard mailing list:
I suggest that if you have water in your fuel tank, the best solution is to remove it. Using alcohol [additive] in the fuel may damage your injection pump and injectors. Properly designed tanks will have a "low spot" in the bottom and an ullage opening (for a sounding rod) in the access plate. If so, you can use a handy-billy pump like the ones used for oil changing to withdraw the water. Otherwise, pull the access plate, pump the fuel off the top and then pump the water out. You can use water-finder paste to find where the interface is. This latter method should be done every few years anyway; while you're at it, you'll find yourself looking at all those "hidden" things like fuel hoses which really ought to be looked at more often. When you're done, the tank should be completely wiped out and dried. You may be surprised at what you'll find in there.

When you're finished, you'll rest easy with the knowledge that you won't get caught changing fuel filters while in a bad spot on a stormy night. That peace of mind, IMHO, is worth even many days work.

From Mike Toledano on Cruising World message board:
My experience has been that rebuilds on old diesels are pretty much a waste of money and time - unless you do all the labor yourself (and know what you're doing). The cost and trouble of getting the old engine out and putting it back in again, plus the labor and parts on the rebuild, in my experience, are usually a very large percentage (70% ?) of the cost of a new engine.

From "Installing a New Auxiliary" article by Don Casey in 4/2001 issue of Sail magazine:
One gallon of diesel fuel will produce around 16 HP for 1 hour. So the average load on a diesel engine can be estimated by multiplying fuel consumption (in gallons per hour) by 16.

David Pascoe's "Drive System Alignment"
"Do It Yourself Engine Alignment" article by Don Casey in 6/2001 issue of Blue Water Sailing magazine.
Jack Harden's "Get In Line"

From "Do It Yourself Engine Alignment" article by Don Casey in 6/2001 issue of Blue Water Sailing magazine:
My idea: after checking and fixing alignment, I would run engine a bit and then check alignment again. Repeat until no fixing is needed.

Replacing engine mounts:

From Lew Hodgett on The Live-Aboard List:
After having gone thru several engine mount change-outs because my Yanmar YSM12 could snap 3/4-16 engine mount studs like they were old pretzels, I found the Aqua-Drive and installed it.

The Aqua-drive is basically a CV joint that allows the engine to bounce around freely on soft rubber mounts and definitely does not require, even want, engine-shaft alignment.

After installation, the noise level dropped at least 25 dB, screws quit backing out of things because the vibration was reduced, and it quit snapping engine mount studs.

Without question, the boat I'm building will have one.

IMHO, it is the best money you will ever spend.

From Roger Rippy on The Live-Aboard List:
Having never tackled motor-mount replacement before, I was a little apprehensive. But looking back on the project, it was a piece of cake!

First thing I did was borrow a small hydraulic lift kit that contained several different types of expansion lifts that attached to a hydraulic hand pump by a 3-foot hose. This really made it easy. I then sprung for all 4 motor-mounts ($400). I figured if one was bad, they probably were all on their last legs.

I then carefully measured the clearances and adjustments on the existing mounts, since the motor was fairly well aligned. I disconnected the shaft coupler, took off the top lock nuts from the old mounts, and jacked up one mount at a time and replaced it with a new one. I set the lower adjustment nut to the clearance of the old one on each of the mounts. The hydraulic lifts helped because there is not a lot of working room around an auxiliary on a Bristol 31.1 !

After replacing the mounts, I reconnected the shaft coupler and used a pry bar to get the alignment close and then I proceeded to align the couplers using a feeler gauge and a little patience. I am glad that this project is over!

Replacing head gasket, from Gary Elder:
One of the biggest risks is breaking a head bolt or a head stud (I don't know which you have). If that happens, removing the 'remains' can be a bit intimidating. I've had it happen to me, and I had to drill out the broken portion of the bolts - with a hand-held electric drill, without damaging the female threads in the block.

Another consideration is cleanliness. All the crud that can fall into the cylinders when you remove the head and gasket must be removed before you install the new gasket and head. Sometimes small pieces of 'carbon', or even gasket material, will fall between the piston and cylinder wall, above the top ring - ya gotta remove that crud before the head goes back on. Don't let any seawater get into the cylinders either.

Also, you will need a torque wrench, probably in the range of 75 - 150 ft lbs. They can be rented from the better equipment rental companies. You will need to find out what the actual torque specs are, and the tightening sequence for YOUR engine.

When removing the head and/or valves, don't mix components; keep the valves, rocker arms and push-rods sorted out in matching sets. That way, you won't have to adjust the valve clearances (much) after reassembling them.

Removing gaskets, in general, from NAPA Auto bulletin:

Dealing with a seized engine (seized because of rust/disuse):
From Arild Jensen on The Live-Aboard List:
... Remove the injectors, pour penetrating oil into the cylinders and let it seep in. Refill every few days as necessary.

[Try] to slowly force the crank over by applying a four-foot bar bolted to the flywheel.

Repeated applications of penetrating oil and continual movement may eventually free up the pistons without damage.

The worst thing you can do is try and rush it, or try and run the engine as soon as you free up the pistons. If you can free the pistons, continue to turn over the engine by hand, while adding lubricating oil. This will help minimize the amount of scoring to the cylinder walls. It will also minimize the possibility of breaking the rings while they are still in the piston grooves.

If you do find actual water in one or more cylinders, first try and suck up the water with a thin plastic tube, then use something like WD-40 which does displace water. Fill those cylinders completely. Don't let air in to sit and allow more rusting.

Patience and perserverance could well save you a bundle of $$$ and an engine.

From Mark Mech on The Live-Aboard List:
If you can free it up with Kroil or some other penetrating oil, turn it over a few times, then fill each cylinder and suck out the oil to remove some of the debris.

Once you start and run the engine you will need to run it for a while to see if the rings re-seat.

If the compression is still weak after couple hours of run time, you can try this next step.

This sounds radical, but it works on engines with poor compression due to rings.

You mix some Bon Ami with water and slowly pour it down the air intake or carburetor while reving the engine. It is slightly abrasive and will polish the rings and cylinders together without scoring anything. Repeat the process several times and check the compression again.

Jesse Brett's "Replace Diesel Engine"

From SC Seaside on SailNet's Gulfstar mailing list:
I've been a mechanic for 40+ years and any first-rate mechanic should be able to tell you whether your problem is a valve job or a complete rebuild. A previous writer suggested using a heavy gear oil to test your compression and this usually produces a pretty good result. Expect to smoke up the yard/marina a lot when your fire the engine back up. As previously stated, if the compression improves dramatically with the oil in the cylinder, you need a ring job.

I have a Ford 120 in my Gulfstar 43 MS and we rebuilt her bottom to top without removing the engine from the boat.

We removed the head and had it reworked at a local machine shop. This included replacing all valve springs, valve guides, milling the head, and grinding and reseating the valves. Total cost, $750.
New injectors, $420.

I purchased a new crankshaft, main and rod bearings, new compression and wiper rings, and honed all cylinders. Total cost $680. We re-used all pistons, pins, and connecting rods.
Water pump $65.
Gasget set, $125.
Misc clamps and hoses, $25.

Of course we did all the labor, which is the main cost associated with this undertaking, but she now purrs like a kitten and at a fraction of the cost of a new engine or having to pay outrageous labor charges. Not to mention ripping out the cockpit floor.

If you've got as much room around your engine as I have around mine, I would suggest you entertain bids from local diesel mechanics to rebuild her where she sits, if that's what is needed. Be sure and put plenty of absorbent in your bilge and change it regularly, seal off the engine room as much as possible to prevent smelling up your cabin and vent, vent, vent. We did the project over the winter and even with the cold outside, it got pretty steamy in the confines of the engine room at times.

From BMW Touring on SailNet's Gulfstar mailing list:
We have a Gulfstar 50 MkII. I had the Perkins removed by means of a cable lowered into the engine room which is attached to the engine lifting lugs using a lifting bar.

This is done via the round access plate put there for that purpose just forward of the steering pedestal.

The engine/transmission are unhooked from everything, then lifted and slid forward into the companionway using timbers placed under the mounts and a come-along. The engine is removed from the boat straight up by a crane and that's it.

Personally, after having gone through all of this - I think an in-boat rebuild is the way to go.

From Arild Jensen on The Live-Aboard List:
Re: hoisting engine: A word of caution.

Slinging any load from the boom which is supported by a halyard to the masthead will create an effect similar to having that same weight suspended from the mast top.

This will cause a lot of heeling.

Because you have removed the engine from the hull you no longer have that ballast effect to assist with righting moment. Therefore the heeling amount will greatly increase.

My recommendation would be to use a gin pole crane or else a tractor with a bucket or similar to lift the engine from boat to shore.

The last thing you need is a stability issue dropping the engine overboard at the last moment.

How much can it cost to have the yard guy help with the tractor for half an hour?

From Mike on World-Cruising mailing list:
Re: Repowering a Cruising Sailboat:

One caution for replacing an Atomic 4, it is important to keep the same prop rotation direction. Many boats have the prop shaft at an angle to counteract prop steer; if you reverse the rotation with a new engine and transmission the boat may not want to steer properly under power.

Jury-rigging coolant system, from "Bypassing a Raw-Water Pump" article by Patrick Childress in 11/2001 issue of Sail magazine:

From Brett in Benner Bay:
If leak from fresh water (antifreeze) coolant system into oil system, drain both systems and refill both with oil (lightest possible is best in coolant system). Engine will run a bit hot, but leak will now be harmless.

Search my site