Skip to main content

How to Evaluate an Engine

Engine Intelligence

Buying a boat? Add these steps to your engine survey to make sure there are no ugly surprises later.

So you’ve found your next ultimate boat—you know, the one you’ll never sell. Just like the last one.

You’ve made an offer, and it’s been accepted. Now comes all the not-so-exciting folderol that will ensure your dreamboat really is a dreamboat and not a nightmare. At the top of the list, of course, is a hull survey. Prudent boaters don’t scrimp here, and the not-so-prudent are usually saved from themselves by financing institutions and insurance companies that demand one before they get involved. Besides, we all have at least one tale of a survey that turned up something truly scary and saved the buyer grief and greenbacks. 

But what about the engines? How do you determine their health and well being, which, when you consider the cost of repairing or replacing them, should make them one of your primary concerns? There are few guidelines on what makes a good engine survey, so many boaters simply turn the job over to the hull surveyor who then typically turns it over to a mechanic. He performs a series of tests and inspections, and based on these findings, presents you with a report declaring his opinion on your soon-to-be motor’s state of health. Because there is some variation (to put it mildly) in the extent of such testing and the validity of such opinions, you should feel comfortable that the process is sufficiently deliberate to find any potential problems. In my experience, the bare minimum for a good survey is a thorough visual examination looking for things like leaks, corrosion, and degraded drive belts, a compression test, and spectrographic analysis of the lube oil. 

Check out FLIR’s video of this engine starting up here

A thermal image of an engine running

But being the bare minimum, you should consider all this only a first step. Not to cast aspersions, but after all, it’s quite easy to tidy up an engine with some cleaner and touch-up paint, and an oil analysis will look pretty good if it was conducted right after an oil change. So what additional steps should you, the prudent purchaser, take to protect yourself?

One takes place before a mechanic even steps aboard: Ask to see the boat’s maintenance records, which will give you a picture of how well this owner cared for his engines and alert you to any repairs that were suggested but haven’t yet been made. If your seller demurs on forking over the paperwork, whether because the dog ate it or he does all his own maintenance himself (but doesn’t bother to keep any receipts), the phrase caveat emptor—buyer beware— should quickly come to mind.

Assuming you do get the records and everything looks good, you can move on to the actual “engine survey.” I’ve always followed two inviolable rules here: One, the owner should be present for it (and for the hull survey as well) if at all possible, although a trusted captain often serves as an adequate proxy. Two, the mechanic/technician must actually be on the boat when she’s underway—preferably during the sea trial. Note the term “underway;” running the engines while the boat is tied to the dock does not qualify. The motors must be up to operating temperature for a valid test, and the only way to get them there is to put them under sustained load. Yes, this is going to cost you more money but it is not at all uncommon for engines to pass a dockside muster with flying colors only to produce disconcerting knocks and squeaks when the pedal’s to the metal. A good mechanic can learn volumes about an engine just by the sounds it makes and how it behaves under load. Here’s an example:

I once attended a sea trial of a boat whose engines appeared flawless—not a scratch or smudge. Everything went swimmingly underway until the mechanic donned ear protection and announced he was going to venture into the engine room with his infrared temperature probe while we were at speed (a sure sign we’d hired the right guy). Once inside he aimed the laser at each exhaust port, noting the temperature reading, and quickly determined that two ports were significantly colder than the others. As it developed, despite absolutely no indication of sub-par performance during the trial, those cylinders had faulty injectors that would have otherwise gone undetected. The owner was duly informed and agreed to have them replaced and, of course, pick up the tab. The client bought the boat and everyone was happy.

The fact that most surveys go off without a hitch should not lead you to complacency. The potential consequences of skipping what can sometimes seem like a formality, financial and otherwise, are too grave to take anything for granted. Especially a pair of pricey engines.

Want to learn even more? The diesel engine is the beating heart of your boat. Arguably, a good running engine is your most important single piece of safety gear. Diesel engines are economical, long-lived and reliable, yet there are a number of ways in which they can fail. This seeming contradiction brings us to the distinction that has shaped the Online Marine Diesel Maintenance & Troubleshooting course.Sign up today and use the coupon code: POWERMOTOR for 15% off.

This article originally appeared in the May 2014 issue of Power & Motoryacht magazine.