Fuel Economy

"In light of the fuel prices,

"In light of the fuel prices, could someone please advised me if running my twin 120 Lehman at 13,500 RPM or some where below 18,000 harm my engines, and is the fuel savings worht the low RPM. Always appreciate your response! Thank you."

"To start with, you should be

"To start with, you should be talking about 13 HUNDRED RPM not 13 THOUSAND RPM. A lehman will self destruct long before you get it up to 13,000 revs.

Anything above about 1500 RPM will create enough heat to keep the carbon at a minimum and your engine life will probably not suffer. Below that RPM range and you may see that the temperature does not come up to 180 degrees (give or take a few) When a diesel doesn't come up to temperature it doesn't burn the fuel as completely and efficiently. Some of that unburned fuel deposits itself on the rings and pistons, eventually causing additional wear and blowby.

One can run at slower RPM's if you bring it up to speed 2000 RPM or so for 15 minutes every so often. Some advise as often as 2 hours of slow running, some say after every 4-6 hours of slower running. The higher speed will bring the temp up and let it burn off the deposits. The time at that speed is important to allow it to completely burn, so don't just run it up for 5 minutes and think you're doing all you need to do.

Economy wise you will see a marked decrease in fuel use at 1500 versus 2000. I run my engine at 1750 which is a comfortable sound and speed for my boat. I burn 2.1 GPH in my 120 Lehman at that speed.

K"