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Does cooler air temps, say 55-65 degrees, condense the fuel on a diesel to put more fuel in to the cylinders verses hot temps say 85-95 degrees to make the engines perform better in rpm & hp? And how much rpm difference would it make if they are right now turning 2800rpm under load with clean under gear & new bottom paint, but going to be another 2000# added in persons, gear & fuel added? I'm hoping to bring the rpm down to 2650rpm by the extra weight and summertime temps and allow for dirty bottoms so they will still spin up to rack and not load the engines so close that they fall under 2600 @ wot when everything is loaded. Cummins 6bta/250hp 89 model CPL1247

R,
DQ

While Bruce is answering that, I was told at the boat show that the older Cummins 6bt's will burn out their injector pumps with the new low-sulphur fuels as a result of its lower lubrication. An additive is a must. True? He suggested an additive called Cetane 8 at every fillup. Your opinion would be greatly appreciated. Walter

Walter,

I use a brand called Lucas Upper Cylinder Lubricant additive that is added to mine when refueling.

DQ

Dug,
The atmospheric pressure, temperature and humidity all affect the density of the air.

On a hot day, or at high altitude, or on a moist day, the air is less dense.

A reduction in air density reduces the amount of oxygen available for combustion and therefore reduces the engine horsepower and torque.

Fuel quantity is not an issue.

Density/altitude also affects take off distances for airplanes.

I doubt you'll notice anything in your setup between the two temps in performance.

I also doubt another ton of weight will drop the rpm down 150 rpm.

When I was on UV's 31 from the Ticfaw to Venice to Pt Eads we had it loaded to the gills with coolers, gear and guys. Well over a ton and he lost no performance. Scuppers were under though.

That's one nice thing about the 31 and its dead rise. It takes a lot to drag it down.