"On The Spot Engine Check"
A preliminary engine inspection can help you decide if that boat you’re thinking of buying should make the first cut. Here’s what to look for.

by Frank Lanier
Chesapeake Bay Magazine 2003

     Boat shopping is an exciting, maddening exercise that can test the tolerance of the most patient human. Much of the maddening part has to do with trying to discern a boat’s flaws before you buy. Obviously a reputable marine surveyor can and should be consulted, however, who can afford the expense of having every promising prospect hauled and surveyed?

     If you want to narrow the list down to an affordable few, consider doing your own “pre-survey” of the boats and one of their most important (and expensive) pieces of equipment—the engine. A well-prepared approach lets even the average Joe make an informed decision. In this case, we’ll be talking about how to pre-survey a diesel engine.


The Once Over

     First, tell the seller up front of your plans to evaluate the engine, and ask him not to warm it up before you arrive (we’ll discuss why in a bit). Just to be on the safe side, nonchalantly check the manifold to see if it’s warm when you get there. How an engine looks can offer valuable clues about its overall condition. That’s not to say that shiny, seemingly new engines are trouble free, but if it’s a real mess on the outside, chances are the owner hasn’t exactly been a stickler for regularly scheduled maintenance. Take a few moments to step back and view the engine and associated systems as a whole, noting any obvious problems such as leaks, excessive rust, broken components, etc. The engine itself should be reasonably accessible so you can perform routine maintenance with minimal contortions. Take special note of any hard-to-reach components, since those are most likely to have been neglected.

     Ask to see the maintenance log. Its very existence bodes well for the engine’s care. Check that entries are current and that required maintenance items are up to date. Also check engine hours and the date of last rebuild, if any. Manufacturers usually schedule rebuilds; they’re normally carried out every 1,500 hours, something to consider if the engine has high hours. This is also a good time to ask about work orders or receipts the owner may have saved—not only to identify recurrent problems but also to see what major work has already been done.

     Bring along litmus paper and, if you have one, a hydrometer—to check the coolant pH level and antifreeze properties of closed systems before starting the engine. Coolant should be clear, possibly with the familiar greenish-yellow tinge common to most antifreeze. Lack of antifreeze or coolant conditioner should make you concerned, as should coolant with a rusty color or an unusual amount of solids.

     Check and record all fluid levels—engine oil, coolant, transmission and reduction gear oil, and steering fluid reservoirs. Keep in mind that a slightly low engine oil level might be okay, but higher than normal levels could be a sign of trouble, especially when the oil is milky—an indication that water, antifreeze or transmission fluid is present, which might indicate mean anything from blown gaskets to a cracked block.

     Rub a little engine oil between your fingers. If it feels abrasive or has a burnt odor, be concerned about bearing wear. It could also simply mean the oil hasn’t been changed regularly. Taking oil samples to a lab for testing is more scientific, but it’s normally most useful in tracking issues over the engine’s lifetime, rather than for spot-checking. Still, a one-shot oil analysis can show unusual wear and the presence of water, antifreeze or diesel fuel. Think of it as a blood test for the engine—it may not predict a heart attack, but it can indicate high cholesterol.

     As for transmissions and reduction gears, dark and sluggish fluid or oil with a burned smell may indicate drive cone problems and a costly rebuild in the near future. After running the engine in gear a bit, use the dipstick to get a transmission fluid sample. Put it on a piece of paper, inspect it under a bright light or in direct sunlight for metallic specks—a sign of significant transmission wear. Inserting a long, thin magnet (the kind mechanics use to retrieve dropped bolts) through the dipstick opening and “sweeping” the bottom of the gearbox may produce interesting results as well.

     Most well-designed engine installations provide a drip or sump tray to prevent oil and other engine fluids from reaching the bilge. These should be relatively clean and dry; excessive water can cause corrosion problems, especially if the bottom of the engine is constantly immersed. If there isn’t a catchment, check for clean absorbent pads beneath the engine, another subtle hint about the owner’s maintenance philosophy and overall attention to detail.

Inspect engine beds and mounts closely for cracks, broken bolts or looseness. Worn, failing or undersized engine mounts can cause a multitude of problems, such as shaft misalignment—a situation leading to excessive vibration, possible shaft damage and premature failure of other components like cutless bearings, stuffing boxes, transmissions or even the hull itself. If the engine mounts are the vertical stud type mounted in a solid rubber base, check that each are centered properly while the boat is at rest. If cocked or leaning to one side, the mount is stressed and the drive train system needs alignment.

     While inspecting the rear mounts, grasp the propeller shaft and give it a strong tug horizontally and vertically to detect any looseness or wear in the transmission or stern gland. Inspect belts for cracks, fraying or delamination, and wiring and electrical components for corrosion, charred or broken insulation, looseness or any other signs of damage. Check cooling and exhaust systems for worn or cracked hoses while verifying that all are double clamped with stainless steel clamps at both ends. Damaged or failing hoses, as well as leaking or new freeze plugs, may mean the engine has overheated at some point in the past.

     Raw water-cooled or open systems are prone to sediment buildup, especially those run in saltwater. Internal engine passages may be completely clogged (which leads to engine damage) even though the flow of cooling water at the exhaust appears normal. Taking the engine apart is the only way to fully determine the cooling system’s condition, but you can get a feel for it by looking at some of the more accessible parts. Most thermostats are easily reached and simple to remove; ask to have it pulled so you can look it over. Some buildup is normal, but serious clogging is a sign of real trouble.

     Engine risers are also prone to clogging in raw-water-cooled systems, so if it hasn’t been pulled and inspected in the last four years, plan on doing it immediately if you decide to buy the vessel. Leaks in general are the engine’s way of telling you something is wrong, and it’s a sure bet if you see them on the outside, they’re leaking internally as well.


Engine Trials

     Although sea trials are normally conducted after some type of formal agreement is reached with the seller, most will at least start the engine and let you observe it at idle and with the transmission placed in forward and reverse while docked or moored. Engine trials lasting a couple of hours allow more time for less obvious problems to show up,but even a 10 minute demonstration can provide valuable information. After the owner or his representative fires up ol’ Betsy, observe the following:

1.      How hard was the engine to start? Did it crank without hesitation or was the owner forced to employ threats, curses and enough starter fluid to kill a moose? Although diesel engines have no ignition system, some do have glow plugs to assist in cold weather starting. Are these operational and were they used? Weak batteries may be to blame, so don’t leap to conclusions. Remember that a pre-warmed engine could be a clue that the owner was trying to recharge weak batteries. Note any battery chargers nearby or even still attached to the batteries.

2.      Examine the engine overall, while looking for those fuel, oil, coolant or water leaks that magically appear once the engine is running (probably because the conscientious owner wipes them up prior to each showing), as well as exhaust leaks, loose components and excessive vibration. Verify adequate water discharge at the exhaust outlet if it’s a wet system.

3.      Listen to the engine. Does it run smoothly at idle and under load, or does it idle unevenly and stall out when the transmission is placed in gear? Have the owner rev it up to about 2000 rpm (unloaded) four or five times to check the smoothness of the throttles and how the engine responds. Rough running can be caused by anything from clogged fuel filters to compression problems, while engines idling at more than 800 rpm may have been set high to mask idling problems.

4.      Verify function of the instrument gauges at all operating stations, noting any abnormalities in oil pressure, operating temperature, the charging system or inconsistencies between the gauges themselves. During longer engine trials, try measuring the engine’s surface temperature at various places using an infrared heat measuring gun or other such device. Compare results with the temperature gauge and engine manual specifications.

5.      Read the smoke signals. A well-maintained engine may smoke when initially cranked or while idling, but not under load. White smoke during startup of a cold engine is normal, but it should clear up after the engine warms. If it continues, it normally means unburned fuel. Common causes of white smoke are cold ambient air, water or air in the fuel, water in the cylinders, a faulty injector or injection pump, incorrect engine timing or poor compression.

Black smoke upon startup is common as well, but its presence after the engine is at load indicates incomplete combustion. Possible causes include air intake or exhaust restrictions, compression problems, lousy fuel, faulty or worn injectors or the engine not reaching its normal operating temperature (for example, a stuck thermostat).

Blue smoke means the engine is burning oil, which is also not uncommon at startup. Continued smoking may indicate trouble with valve guides and stems, worn piston rings, failing turbo-supercharger oil seals or excessive oil level in the engine.


The Final Analysis

     So what does it all mean? If the engine passes everything above with flying colors, is it good to go for another ten years? The answer is a resounding . . . maybe. While the practiced ear and diagnostic skills of a knowledgeable marine mechanic are essential to determine an engine’s condition, even the most glowing survey report doesn’t guarantee that you won’t be paying for an engine rebuild or replacement later on. That said, a careful preliminary inspection followed by a professional survey is still the best offense a buyer has against unexpected engine woes.