Tips for Repowering Your Boat

Should you put a new engine in your old boat?

February 1, 2003

Own and operate any boat long enough and you’ll face this costly choice. Your engine will need major repairs, or it will need to be rebuilt or replaced altogether. If you choose to replace your old engine with a new one, know this: There’s a lot more to repowering a boat with a stern drive or an inboard than just swapping engines.

Before you start, find out if the job is worth the money. Rarely does the market value of a boat increase enough to justify the cost of repowering. It’s often smarter to simply repair your old engine or install a rebuilt engine instead of a new one, then sell or trade in your boat, moving up to a new model.

How much will your old boat be worth with new power? To find out, log on to for an estimate. Also, if you own an older, larger model, hire a marine surveyor to evaluate your boat’s worth. It may suffer from other problems that would make repowering pointless. Of course, if you plan to own the boat for another dozen years or so, the cost of repowering may be significantly less than buying a new boat.


Your next task is to find out why the engine failed. Marinized engines rarely wear out, especially during the first 10 years of operation. Usually it’s problems with components or poor maintenance that cause engine failure, not wear and tear. Unless the cause of the failure is determined, you may be wasting your money-especially if you’re buying the block and intend to use the same alternator, starter, pumps, wiring harness, and so on. Each component should be tested before reuse. If your boat is an I/O, you may want to consider a new outdrive or, at the very least, having your existing outdrive rebuilt. There could also be problems associated with the airflow in the engine compartment. Or you may need to check out the drive train, including running gear and alignment.

Once you decide that new engines are the best way to go, complete this checklist before completing the job.

1. Get a list of half a dozen similar repowering jobs recently performed by the yard, including customer names and phone numbers.


2. Call these people to determine their satisfaction level.If you’re converting from older, heavy diesel engines to new, lighter diesel engines or to gas, your boat’s center of gravity will change, which could cause handling problems.

3. Contact the boat’s manufacturer to see if it has any data on similar changes or have the plan reviewed by a naval architect.

4. If you’re increasing horsepower, you may need structural changes to increase airflow in addition to new shafts and struts. Again, get expert opinions and have the yard include any such requirements in its quotes.


5. Will a larger engine or engines leave room for access once installed? Make sure to map this out before you start.

6. Can your existing electrical and gauge systems handle the requirements for the new engine? You may want to consider replacing the gauges with an engine monitoring system to take advantage of the new engine’s technology.

7. Will your existing controls be compatible with your new engines? It may be necessary to install new controls.


8. If you’re converting from gas to diesel, you’ll face additional costs of fuel tank modifications for return lines and valves. Galvanized steel fuel intakes shouldn’t be used with diesel fuel.


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