Engine cooling water flow?

[pwilletts]

anyone care to estimate what the rate of cooling water flow is in a 6hp diesel engine.at normal rpm ..gph and psi??

[tkeithlu]

Let's see. It's an impeller pump, so pressure is going to be dependent on constrictions in the discharge, such as the bib to the mushroom, and vary inversely with flow, so we can't compute that one without seeing the system. Guesstimating from my larger propulsion and genset engines, I'm going to say 5 GPM or less. Put a bucket under it and find out. Why? Careful...If you are thinking about using it as an emergency bilge pump, that's a issue that sparks very strong feelings, with some people who know far more about it than I do saying never do it.

[sailorchic34]

Conservatively 3 gpm at 15 feet. Actual probably ballpark, a tad less then 2 gpm at 10 feet. Head required would be a function of pressure drop through the heat exchanger and is not know.

[GordMay]

According to Jabsco:
“On average, petrol engines and fast-running diesel engines with direct cooling require a raw water flow of about 36-39 litres (8 - 8.5 gallons) per minute for each 75kW (100 bhp) of engine power. Engines with indirect cooling require more flow: about 65-70 litres (14.5 - 15.5 gallons) per minute for each 75kW (100bhp) of engine power.”
➥ https://www.jabscoshop.com/advice-an...ling-pumps.htm
➥ Engine Cooling > Misc Pump Wizard Articles > Xylem Flow Control - Let's Solve Water.

[bauer965]

I agree with something along the realm of 2-3 gpm on an engine that small since 40hp range engines are about 5gpm. Depending on configuration, since an engine that small likely has a smalle exchanger, any flow much higher could produce excessive flow rates in areas, which could contribute to erosion.

[exMaggieDrum]

Originally Posted by GordMay

According to Jabsco:
“On average, petrol engines and fast-running diesel engines with direct cooling require a raw water flow of about 36-39 litres (8 - 8.5 gallons) per minute for each 75kW (100 bhp) of engine power. Engines with indirect cooling require more flow: about 65-70 litres (14.5 - 15.5 gallons) per minute for each 75kW (100bhp) of engine power.”
➥ https://www.jabscoshop.com/advice-an...ling-pumps.htm
➥ Engine Cooling > Misc Pump Wizard Articles > Xylem Flow Control - Let's Solve Water.

That sounds pretty definitive. Since the OP states he has a 6hp engine he should need, at a minimum, 6/100x8.5= 0.5 gal/min if direct cooled. And 6/100x15.5=.93 gal/min if indirect cooled. I was imagining that a small engine like that would not need, nor spit out, very much at all. I would be surprised if it put out 5gpm. 1gpm seems pretty low so not sure if the studies scale down well to that small a motor. I suspect not.

[bauer965]

As a marine engineer, I can tell you not all design is based on directly proportional relationships. There are always minimums and maximums, and other constraints, that in conjunction with all the system components, drive the sizing of each component. Most systems whose performance falls near the extremes of the range, typically do not follow the prescribed rules of thumb.

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