Mariners considering the purchase of a boat with Detroit 71 or 92 series engines often inquire as to the life expectancy between rebuilds. Answers vary widely from 2,000 – 5,000 hours, but many captains find themselves rebuilding at 1,000 hours. At $40,000 per engine for a complete rebuild, that yields an operating cost of $80/hr. before any fuel or maintenance...ouch! So why are so many engines meeting an early grave? Following is a summary and analysis of some of the answers found on yachting forums.
“You have to run ‘em or they die.” You’ll often here this from experienced captains and mechanics alike. While there’s no hard data, anecdotal evidence shows many charter captains report getting 3,500 – 5,000 hours from a turbo-charged 92 series engine, whereas pleasure captains that use them much less frequently are rebuilding at 1,000 hours. I’ve experienced this with my own Viking 48 (twin 8V92 TIB’s), that did a flawless run from New Orleans to Annapolis (2,000 Nautical Miles), and then cracked a liner a year later when I was refurbishing the interior and hadn’t run her much that year. I believe the reason for this disparity in longevity is driven by five factors:
First, no matter how diligent we believe ourselves to be, frequent use of the boat compels the us to be more attentive to maintenance. It’s just human nature. Whether you’re making a run from Boston to Florida, or back and forth to the canyons every day, you develop a checklist and pay careful attention to every detail of maintenance. You’re checking fluid levels every day, monitoring fuel usage, watching oil burn. You sweat the details because your livelihood depends on it. When you only take the boat out once a month, you tend to get lax. You know you topped off the coolant not too long ago, so no need to check it this time. Just walk to the helm and fire her up! You rely on your memory, our memories betray us.
Secondly, frequent use makes the captain attune to the idiosyncrasies of the vessel’s performance. You know how it sounds. You know how fast the temperature should climb as it warms up. You know under what conditions it should smoke. When anything doesn’t seem quite right, you check it out. Infrequent users forget these details quickly with time. Chances are, all you have at the helm are tach, temp, oil pressure, and transmission pressure gauges. By the time any of your alarms go off (and you figure out what's wrong and respond to the alarm), you've already blown a sleeve seal or spun a bearing and you're doing a rebuild. A pilot who runs the boat every day can smell that something’s not quite right, even before the gauges reveal it.
The third element is the marine environment itself. Corrosive salt in the air finds its way into open valves and intake ports when the engine is sitting. The thin film of oil on the cylinder walls will last for a few weeks, but after that rust begins to eat away at the precision surface of the sleeve, reducing compression. Run the boat once every few weeks, and a different port will be exposed to the salt air, evenly disbursing the wear across all your cylinders. Meanwhile the charter captain is running his block heaters every night to keep the engine warm and ready to fire at 6:00am for the next day of fishing. While the pleasure craft is sitting on the hard for the winter, the charter boat has relocated to warmer climes, and continues its relentless pursuit of billfish, all the while keeping those cylinder sleeves clean and dry.
The fourth horseman of the Detroit Diesel apocalypse is Shallow Water. Charter captains tend to do most of their running in open seas and areas they know well. Pleasure captains tool around the bays, harbors, and the ICW, which are often poorly marked and subject to shifting shoals. In the Chesapeake Bay we like to say “It’s not a matter of if you’ll run aground, but when.” Wandering into shallow water results in silt or sand being ingested by the engine intakes, and soon results in overheating. This is especially a problem when the inexperienced pilot tries to back off the shoal and finds the dreaded reverse gear, pumping billows of silt forward to sea strainers. Like any wet-sleeve diesel, Detroit 92’s are highly susceptible to overheating, and the damage may not make itself known until months after the event. 92’s can blow sleeve liners above 195 degrees, mixing coolant with the oil and quickly destroying bearings. 71’s tend to crack heads above 200. Most alarm switches are 210 – the equivalent of a “wing off” light on your Beechcraft Bonanza.
The final factor Detroit longevity is, as with any mechanical system, pro-active, diligent, and competent maintenance. Fortunately, there are still many highly skilled marine mechanics around who know the old Detroits, but it is an aging population and their numbers are shrinking every month. But no matter how competent or ethical your mechanic is, he will never be as committed to the longevity of your engines as you are. It’s just human nature…we focus our attention on the things that have the potential to cause us pain. Pleasure captains who rely on their mechanics to be on top of all maintenance issues will find themselves doing 1200 hour rebuilds. Charter captains know they have to be experts on their powerplants to ensure longevity, and they typically operate in a community of other captains who share knowledge, experience, and best practices. This gives their engines a significant leg up for survival over those in a pleasure craft whose mechanic only sees the engine at scheduled oil changes and when something goes wrong.
So how does the occasional pleasure cruiser stretch the life of his Detroit mains? Here are five suggestions that will definitely help:
#1. Create Operations Checklists. Just as a 737 pilot has a pre-flight checklist that gets completed before every take-off, you should have written pre- and post-voyage checklists on a clipboard that you complete every time you run the boat. Work with your mechanic to make up the list. Have one of your crew members read the list and check off items as you work through them. It gives them something valuable to do and frees your hands.
#2 Upgrade your charts. Don’t buy a 5 year old chartplotter on eBay and assume that the chip in the guy left in the chart port will be good enough. You need up-to-the day accuracy on your charts to prevent grounding. New charts can be expensive, but worth every penny if they prevent you from running aground. If you’re running the ICW, download ActiveCaptain and use review the local knowledge features on your route each day to alert yourself to new hazards. Here’s another important tip: When you approach a marina you’ve never been to before, hail the area for another local captain who is heading in. Following someone who knows the water may cost you 15-20 minutes, but save you a tow or worse. Shallow water kills engines.
#3. Upgrade Your Alarm System. Several companies now make improved alarm systems and sensor modules that will give you better visibility into what’s brewing in your engine. Timbolier Industries is currently bringing to market a retrofit ECM that adds up to 20 sensors to a 92 or 71 series Detroit engine, and allows you to set both upper and lower yellow and red alarm thresholds that adjust to engine speed if needed. You can even set automatic shutdowns in case you’re far from the helm. Essential additions to your sensor array are:
It’s best if the ECM converts all this data to NMEA2000 so you can display it on screens as virtual gauges in addition to driving the alarm module. A unique feature of the Timbolier system is the ability to chart current sensor readings against a baseline. This takes the guesswork out of knowing what's "normal", and allows you to see degrading performance in any subsystem.
#4 Install a low-wattage block heater with a thermostat to keep your engines warm at all times. This will prevent condensation from forming in the open cylinders, and greatly extend the life of your liners and rings. If you already have block heaters, make sure a thermostat is installed! Boiling your coolant by leaving it on all weekend can destroy the nearby sleeves.
#5. Put your TV in the Attic and spend some evenings reading the boatdiesel blogs for a few weeks. You’ll quickly see there are some real experts posting there. Do a search on their handles and pull up all their posts and read your way through them. Their combined hundreds of years of experience will get you up to speed and help you avoid the “school of hard knocks.”
#6. Build a Maintenance Schedule. Every fluid, filter, impeller, and zinc in your engine has a useful life. Find out what they are and build your own maintenance routine. Ask your mechanic or the boatdiesel forum to review it for you. How old is the coolant in your engine? 10 years? It’s only designed to last for three. Assume the prior owner did nothing unless you see receipts. Download an equipment maintenance app for your phone and log everything in. There are several out there for boats, or cross-purpose one made for cars.
#7. Don’t Be Afraid to Over-React. If something doesn’t seem right with an engine, shut it down and head back to port. You’ll hear mechanics tell you how bullet-proof Detroits are – don’t believe it. Detroits have a reputation for getting you home even when damaged, which is great, but it doesn’t reduce the cost of a rebuild. Don’t be afraid to disappoint your guests. There’s always next weekend. Take the money you saved on a rebuild and buy them a lobster dinner. They’ll forget all about the short boat ride.
John T. Cox
Timbolier Industries, Inc.