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Sea Savvy - Is there a doctor in your engine room?

There should be.

Is there a doctor in your engine room? There should be.

Getting up close and personal with a hunk of metal may not be something that really turns you on, but it can make a big difference when it’s time for you to turn the hunk on. It’ll also help keep it purring on cue, like a well-paid porno star.

The hunk I’m talking about is the one in your engine space, and it has a lot of zones that crave attention. When Mel and I are under way, I disappear at least every couple of hours to go down into the dark place for a few minutes of intimacy.

A few years back, we’d spent the summer in New England and had just completed another trip from east to west on Long Island Sound. It was early afternoon, and we’d timed our approach to Hell Gate to coincide with slack tide. Hell Gate is where the waters of Long Island Sound rush into or out of New York’s East River, mixing with the currents from the Harlem River. This small area is like a very deep bowl, with rocky shores and an uneven bottom. At full flow it can become a maelstrom of conflicting currents, whirlpools and standing waves. It’s not a place we like to be except when the tide’s barely running, if at all.

As we entered the final approach, I went down to the engine room for an extra check, as I always do if I’m heading into tight quarters, where it’s even more critical that equipment work well. I’d checked about a half-hour before, but, ever paranoid, I did it again. This time something wasn’t right. I lingered, trying to narrow it down. It was a noise; something didn’t sound right.

I slowly walked around the engine, listening, sniffing and looking. The unusual noise seemed to be coming from the alternator. I bent over it; it smelled hot. I touched it briefly, knowing I could get a bad burn but taking the chance. It was much hotter than usual. What to do? There are a number of potential causes of alternator overheating — for example, it could be putting out excessively high amps, or there may be wiring problems. Either situation can indicate serious trouble.

I checked my digital gauges to be sure the amperage output was OK. It was, but I was still hearing a noise. I wondered if I was wrong about the alternator. I grabbed a long screwdriver, carefully placed the tip of the blade against the alternator, and pressed the hard plastic handle against my ear. Indeed, the noise was coming from the alternator. It was a pronounced gravelly sound, occasionally sharply uneven. There’s always a bit of a gravelly sound coming from an alternator (at least mine), but this was louder than normal. To me, it indicated deteriorating bearings.

When bearings degrade sufficiently, the component turning on them either stops turning or self-destructs. On most engines, you have to shut down if the alternator stops turning. This is because the belt that’s driving the alternator is also driving the engine’s freshwater cooling pump. That belt will quickly disintegrate if one of the pulleys stops turning freely.

One “fix” is to replace the alternator. For me, this is a 45-minute job — longer if I have to remove a pulley from the shaft. Many can’t do it at all because they don’t carry a spare.

Another fix is to rig a smaller belt that encircles just the engine’s drive pulley and the water pump. This also takes time, and you have to have an emergency belt on board. In either case, your engine can’t be running. You can’t drift in Hell Gate, and there’s no place to anchor. By this time, we were reaching the point at which we had to decide whether to abort or head on.

If I had x-ray vision I’d be flying around in a Speedoinstead of running slow boats, and I certainly wouldn’t have spent all that money over the years on depth finders. I couldn’t see inside that alternator, but I could see into the future and knew we’d be in deep trouble if the bearings ground out in the middle of Hell Gate. We wanted to get through because we needed to get down the New Jersey coast to Annapolis, Md., for a boat show — I had numerous talks scheduled — and in a couple of days weather was going to be closing in. Much of a delay, and we’d miss our weather window. I knew what was happening to the alternator, but I didn’t know the stage of the problem, which meant I didn’t know how much running time was left in the unit.

I pulled out my gun. No, it’s not what you’re thinking; I didn’t want to shoot the thing. (Well, I did, but I was afraid I’d miss and sink the boat.) I pulled out my infrared heat-sensing gun and began taking readings at both ends of the alternator. It was hotter than usual, but not by much. I knew this because I’d made a habit of taking readings during normal operation.

As we continued on, the readings remained fairly stable. We made the decision to go through with the slack tide rather than turn back, anchor, replace the alternator, and wait for the next day. (I’d never go through Hell Gate at night.) When we reached our anchorage in the evening and shut down the engine, I replaced the alternator. A big problem had become just a small one. We reached Annapolis on time — and safely.

The ability to feel, smell and listen can help you to understand what’s going on with your engine and to anticipate problems. In many instances, this intimacy can be more valuable than the gauges at the steering station, although these, too, should be monitored closely. People often ask, “What exactly are you looking for?” The answer: anything that’s different or unusual.

It’s a fairly safe assumption that when something is different, something is wrong — or getting ready to go wrong. But to know when something is different, you must first know what’s normal. To do this, use all of your senses, including common sense.


It’s easy enough to stick your head into the engine space and sniff. You’re probably already familiar with the general smell of your well-running engine and the spaces around it. Variations in smell can indicate many problems. For me, sniffing is a key tool to a well-running boat. If a new smell leaves you puzzled, other steps may need to be taken, such as listening and feeling. I’ll talk about these later.

Often an unusual smell is that of paint heating up. An overheating smell can mean some component of the engine is getting too hot; there are a few I suspect first. Overheating of the exhaust water injection elbow can mean the raw water pump is putting out a substantially decreased flow, possibly caused by the impeller blades tearing or a clogged sea strainer. If you also smell the exhaust hose heating up (usually the smell of rubber burning) the situation is critical. The engine, of course, should be shut down immediately.

The heat exchanger tank for the antifreeze/water coolant mixture can overheat for the same reason, although there are other causes, such as a failing freshwater pump. If the freshwater pump is beginning to fail it also may be overheating, because the failure often is caused by bearings going bad. If this is the case the mystery likely will be solved quickly, since bad bearings can cause shaft wobble, which will soon destroy the water seal, causing the pump to start slinging coolant around the engine space. A failing freshwater pump also can result in the smell of rubber burning from the belt because it is meeting high resistance as it tries to turn the water pump pulley against the deteriorating bearings. If a freshwater pump problem has progressed to the point that the seal is leaking, the smell of antifreeze also will be present. It may be so strong that it masks other smells.

An alternator overheating, as was the case above, may mean the bearings are beginning to go bad, which means the alternator soon will fail. It also could indicate an alternator belt that’s too loose or too tight. If it’s too loose, you’ll probably also smell burning rubber as the belt slips. You also may smell the belt if the bearings are near the point of seizing and the belt is meeting higher resistance as it tries to turn the alternator’s pulley.

The smell of an overheating alternator may be that of hot paint or, more likely, hot metal and bearing grease. (Alternators usually aren’t painted.) The grease used on the bearings must be able to withstand unusually high temperatures without running out or burning. But even high-temperature grease may begin to degrade and smell if the bearings are wearing out. You’ll find your alternator can grow quite hot during even normal operations, and that the more amps it’s putting out — as when you first start your engine and it’s bulk-charging your batteries — the hotter it’ll be. It’s the extra-high temperatures you’re checking for, and you should be able to detect them if you sniff regularly, including during times of high output.

If the engine itself is running hotter than normal, rather than an external component such as an alternator, it usually will have a different smell that’s a combination of many things. If you have to deliberately run your engine at unusually high rpm for some reason, such as outrunning a storm, it is especially important to check it, for two reasons. The high rpm probably will be causing it to heat up more than usual, and you can then become familiar with this generalized smell. Also, if there’s a lurking problem previously unnoticed, such as a deteriorating raw water pump impeller or deteriorating bearings in the alternator or a myriad of other possibilities, the symptoms may manifest themselves during this high-rpm run, even though they aren’t yet noticeable at normal speed.

If you sense your engine is running hotter than usual under normal running conditions, check out as many possibilities as it is practical and safe to do. Causes can include some of the failures discussed earlier, as well as other problems, including low oil or restricted water flow to one or more of the heat exchangers or scaling in the tubes within the heat exchangers. Remember, some engines have as many as four heat exchangers. They cool the freshwater/antifreeze block coolant, the lube oil, the transmission oil and turbocharged air. General overheating also can be caused by debris on the propeller. (I’ll talk about this in more detail later.) More serious internal causes, such as main bearings, could require professional assistance.

A jungle of smells

Many other gremlins have special smells. Hot used lube oil, if it leaks out, is usually very noticeable by odor. The source could be a leaking oil line, a pressurized oil pan caused by bad rings, or various other things. Hot transmission fluid also has a distinctive smell when it leaks. The leakage could be caused by a breach in a high-pressure transmission fluid line, a seal failure or a valve problem within the transmission. If you detect either of these odors, you’ll probably have to shut down the engine quickly.

Smells when the engine isn’t running also can point to problems. One of the most frequent, once again, is the smell of antifreeze. Usually it’s in the bilge. This may mean a leaking seal in the freshwater pump (indicating imminent failure), a leak in one of the hoses or a leak in the freshwater heat exchanger seal, usually at an end cap. It also could mean the coolant expanded and escaped from the pressure cap on the header tank when you stopped the engine.

Coolant will expand when you stop the engine because there is no longer cool raw water being pumped through the heat exchanger and the block remains hot and often gets a little hotter for a few minutes. Normally, the expanding freshwater coolant is trapped in its collection tank, which usually is made of plastic. If the engine was running too hot when it was shut down, the antifreeze/freshwater coolant may overfill the collection tank and run into the bilge. Sometimes, one or more of the tubes inside the heat exchanger develops a pinhole leak, allowing seawater to mix with the freshwater/antifreeze coolant while the engine is running. This results in an overflow, eventually into the bilge, which will give off the smell of antifreeze.

Perhaps one of the most frequently encountered smells is that of diesel fuel. Usually this indicates a slow seepage around a high-pressure pipe union, perhaps at an injector or the injector pump. Usually this is easy to fix with a wrench; sometimes it can indicate a much more serious problem, such as a high-pressure line beginning to fail. If one of these begins to crack it can very quickly spray a mist of diesel fuel, under high pressure, out into the engine space. This can ignite with calamitous results if it touches something hot enough, such as an exhaust manifold. A spark from a circuit panel or other source also can ignite it.

While diesel engines normally smell “dieselly” to some extent, sniffing for something unusual can pay off big time. Of course, the smell of gasoline with a gas engine indicates extreme danger. Other smells may indicate immediate danger. Exhaust smell is obviously high on that list. If you smell exhaust, you probably need to evacuate everyone from below deck immediately and proceed with extreme caution. Don’t take chances. Even checking to find the cause is risky. Remember, too, that some dangerous emissions, such as carbon monoxide, don’t smell, even though they kill. The best protection against emissions is an adequate number of high-quality and properly maintained and stationed detectors. These do the sniffing for you and hopefully give you adequate warning in advance.

Another smell that may indicate immediate danger is that of burning or overheating electrical insulation. The odor usually is very noticeable and, typically, fairly easily traced to its source. This can mean a terminal connection is about to burn through, causing loss of power in some component, or it could mean you’re about to have a fire or electric arcing.

Problems such as these can be caused by many things, including low voltage or unusually high consumption. They also can be caused simply by old connections or old wires that have gradually corroded over the years from heating and cooling repeatedly in a moist, salt air environment. They gradually reach a point at which the conductivity is impaired enough to cause overheating and eventually a burnout.

Touching and feeling

A laying-on of hands can detect many developing problems, but this can, of course, also be particularly hazardous if not done carefully. Some parts of the engine can be exceedingly hot, and some parts move rapidly. Most of the feeling I do is to detect heat and vibration.

If you know the feel of a component at normal running temperature, you often can determine well in advance, even before it produces a different smell, that something is going wrong. A heat exchanger is a good example. Depending upon your system’s plumbing, these normally are hotter at the end where the engine’s cooling freshwater/antifreeze mix enters and cooler where it exits after having lost some of its heat to the raw water coursing through the tubes. A decreasing difference in temperature under otherwise similar circumstances (same temperature sea water, same rpm, same loading, etc.) normally indicates the onset of a problem such as a deteriorating raw water pump impeller or scaling buildup in the exchanger.

On many engine installations, you can touch, without getting burned, the pipe where raw water, having done its job in the one or more heat exchangers, is injected into the exhaust line to exit the boat and cool the exhaust in the process. This is usually at or near the top of a loop of exhaust pipe just downstream of the exhaust exit from the exhaust manifold. I’m speaking of touching only the upper part of the injection pipe. Touching the exhaust pipe itself can cause serious burns if it’s not adequately protected or cooled. Usually the injection pipe will cool quickly after you start the engine and cool seawater is pumped through, then slowly warm up as the engine warms. The upper section of the injection pipe should remain relatively cool. Its temperature will vary with that of the water outside the hull and rpm, but you’ll be able to tell if it’s becoming too warm. This could indicate that your through-hull intake or sea strainer is becoming clogged, the raw water pump impeller is deteriorating, or perhaps the raw water is having to remove extra heat via the heat exchangers because of some other problem in the engine.

You’re thinking, Well great, all I’ve got to do is burn the skin off my hands and I’ll have a happier engine. But if you get an infrared heat-sensing gun, you can get a fairly accurate measurement while staying safely back and just pointing and pulling the trigger. I do this regularly with my RayTech, and I keep notes on the computer. Heat-sensing guns require a little skill to use properly. For example, you’ll need to shoot the same spots and from the same distance away, for comparison purposes. If your gun uses a laser spot to pinpoint the target, you’ll find it easier to use.

Feeling for vibration also tells tales. For example, you should know what your hull feels like where the struts are bolted on. Pull up the hatch and lay your hands on the hull in that location. There probably will always be some vibration. But if your prop has debris on it or becomes even slightly bent, or if the shaft or engine is out of alignment, there will be additional vibration.

If you can safely do so without getting yourself mangled in the shaft coupling, regularly check the stuffing box for unusual vibration. It will probably be wobbling a little under normal conditions, the less the better. If you have damaged a prop or picked up a piece of trash, you will feel the difference. I also lay the back of my fingernail on the shaft to better detect any “jumping around.” (This also can be dangerous. Keep clear of the coupling and other moving or hot parts.)


Once I was swamped with business and chores, so I broke one of my cardinal rules and hired a “certified” mechanic to do some engine-room work. While he was sitting on other parts of the engine and breaking them, he installed a new raw water pump. Several weeks later I heard a slight but insistent tapping around the port side of the engine. I looked and listened but couldn’t find a thing wrong. The tapping grew worse, with a little screeching drifting into the melody. When I reached an area where I could shut the engine down and crawl into the cracks and crevices around it, I found that the “certified” mechanic had put the lock washers under the bolt heads holding the pump to its mounting bracket rather than under the nuts. The nuts had begun backing off, and the pump was slowly disintegrating a very expensive Lovejoy coupling. In a few more hours I probably would have had more than $1,000 in damage.

Usually, whenever we go into the engine space all we hear is a deafening roar. But subtle changes in this roar or underlying noises may be giving off clues. As with other sensory diagnostic techniques, it helps to know what’s “normal” so you can know what is abnormal.

I have a regular program of listening. As a rule, it’s advisable to wear noise dampeners over your ears when you go into the engine room. Too much noise can cause hearing loss. I have the dampeners and wear them, but there are times I remove them for short periods to listen better. It’s a tradeoff I don’t like, but one I personally choose to make for safety reasons.

I’ve found that, because of the engine’s roar during regular running and because of startup stresses as components begin to move, it’s very helpful to be at the engine and listening when it’s being started and shut down. Therefore, our usual procedure is to have Mel, my wife, at the helm to start and stop the engine while I’m standing prayerfully beside the beast, hoping I won’t hear anything weird. This ritual has saved us many thousands of dollars over the years.

I talked earlier about using a long screwdriver with hard plastic handle as an aid to listening. Some experienced mechanics do this. Obviously it can be a dangerous practice for many reasons. You have to get close to the moving parts, and you’re probably going to be leaning into them. And if the tip of the screwdriver fouls with a moving part it could cause serious injuries. If you’re going to use a listening tool it’s better and safer to listen with a mechanic’s stethoscope, which looks very much like a doctor’s stethoscope. You can get one from a specialty-tool shop. It has a long probe that is connected to earpieces with a long, flexible tube.

Whatever tool you use, when you touch the probe to the part you want to hear you’ll be amazed at the previously unnoticed sounds coming from the component. I regularly listen to such spots as the head over each cylinder, the side of the block around each cylinder, each end of the alternator, the freshwater pump, the injection pump, the transmission and many other areas.

It’s critical to remember that many of the procedures we’ve discussed can be dangerous. I don’t “recommend” that you do any of this. I pass on my personal experiences because knowledge of options and solutions, coupled with training and experience, is good to have at sea. This is because you may have to choose between two or more courses of action, none of which is “safe” in the abstract, to achieve the greatest probability of safety.

Being on a boat on the water sometimes means you’re on your own in unexpected circumstances, which can seriously threaten your well-being. It may be up to you to weigh the risks and determine which you want to take and which are wise to avoid. For example, if you hear a worrisome noise and you’re a few minutes out from your marina and a good mechanic, it may make more sense to get the boat in and let them take care of it. But if you hear that noise offshore and there’s a storm coming up and you must negotiate a difficult inlet in order to reach safety, you may decide the safest course is to immediately ferret out the noise on your own.

Have fun out here, but use your senses.

Tom Neale is technical editor for Soundings and lives aboard a Gulfstar 53 motorsailer. You can buy his book, “All in the Same Boat,” at