Join Date: Feb 2010
Location: Narragansett Bay
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Re: Additives for 120 HP Lehman Engine?
Yup, blue smoke means burning oil. I'd want to determine why. Could also be the rings are not shearing the oil off the cylinder walls very well. A compression check would be in order.
As for fuel additives, the only mandatory (IMO) additive is a bio-cide. Some marine fuel suppliers, such as Valvtect, already include it, so no need to add more. If your source does not, you want to add it yourself. Bacteria actually grows in moisture in diesel fuel, then die and create sludge at the bottom of your tank. If this is a new to you boat, you would do yourself a favor to clean the tank at some point.
Other optional witchcraft are the variety of fuel stabilizers out there. Although, diesel is inherently more stable than gasoline. There are also additives that will absorb/combine with small amounts of water in the fuel and burn it. Be sure the additive you choose is not made of ethanol, which is the most common water absorber. I use the additive from USA Fuel. I don't need added biocide, nor use a stabilizer.
Since this boat is new to you, I'd consider a really good once over on a few things.
First, be sure the raw water side of the cooling system has been descaled. Any scale will reduce proper cooling. Excessive heat can over expand and warp things and make them work improperly. If you're unfamiliar with how, you need to set up a recirculating process with a descaler, just ask. Check the exhaust elbow and replace if necessary. These are a wear item in the cooling system. Is your boat fresh water (ie coolant) cooled, with a heat exchanger? If so, drain out all the coolant, add a cleaning flush and clean that out well, then replace with fresh coolant. Test or replace the thermostat.
Can we assume all your filters are new: fuel, oil, air? They should be.
Consider running a good engine flush in your oil for 20 or 30 mins, at the dock, then change your oil. I like using engine flush from Amsoil. If its very old, with unknown service, I'd consider draining it out, then adding oil and another flush and doing it twice, before draining and putting in the proper service oil. Sludge is doing bad stuff in there, however, ironically, if the smoke due to worn valve stem seals, the sludge might possibly be slowing down the leak. Doesn't matter, it's doing other bad stuff. Clean her up and deal with whatever is leaking. Proper clean oil passages also help cool.
If the hoses and belts are in good shape, they certainly have nothing to do with this problem. Assuming you get her in good running order and are keep the motor, I like replacing these, just so I know when that was done last. They can both ruin a nice sail, if they let go.
Last thought is whether you nailed the color. Grey can be deceiving. Grey/black is unburned diesel fuel and a whole other series of investigations........
Best with your new motor. If she's starting and running properly, you'll get it settled down.
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In the harsh marine environment, something is always in need of repair. Margaritas fix everything.