6BTA5.9M 250 hp By-pass Aftercooler coolant ?

[Doug Kirby]

Hi,
I have a 40′ displacement vessel with one Cummins 6BTA5.9M, serial No 21022041, CPL 953 rated at 250 hp at 2600 rpm, my normal cruising speed is 7.8 knots at 1700 rpm which represents 99.99% of operation, anything above 1700 rpm burns a lot more fuel for very little change in speed for example 2600 rpm is 8.9 knots. The Aftercooler is coolant cooled, I think they are referred to as tombstone design.

At 1700 rpm the charge air temperature from the turbocharger into the aftercooler is 59 degrees C (124 F) and the coolant temperature is 85 degrees (185 F) so it seems that my aftercooler is heating the charge air which I believe will not be good for economical performance and so it seems that would be a good idea to avoid this.

It looks like the charge air temperature exceeds 85 C (185 F) and so the aftercooler has an effect at higher revs where I virtually never operate except if it was an emergency when that extra knot may be needed.

So I am wondering about by-passing or blocking off the coolant flow to the aftercooler to prevent this heating of the charge air, do you guys have any advice or experience with this please ?

Thanks Doug

Topic

[Tony Athens]

Doug, I think your “thinking” may be leaving out a couple of things…………

Did you measure air temp just after the turbo and inside the manifold under the aftercooler? Not sure what one you are referring to with your 124F temp? But there must be a delta of some sorts.

I do not agree that a cooler air temp fed to the engine under these circumstances will improve the BSFC ( which is “efficiency”….

Realistically , in all test cell data I have ever looked at, the higher the temp you can keep an engine, the better the BSFC.. But then again there are other concerns with higher temps.. Take away heat and you take away potential power, and more so in a turbocharged engine.

The best thing you can do with your 30+ yrs old “953”s as to there longevity and safety is to follow the other posts recommendations…

My 2 cents

[donald roth]

This is an interesting question, one that I have thought about alot.
My current 6BT @ 180 hp does not utilize an aftercooler and I have noted that EGT takes quite a jump above 1700 rpms.
My 99.99% normal cruise is 8K at 1600, so not a big issue, but I think I’d need a smaller prop to run any harder.
I have quite some experience with the 953 motor, and coolant temp numbers can be improved fairly easily by upsizing raw water pump and piping, and changing to 160* thermostat.
I ran raw water through the aftercooler too, but it’s not designed for that, and so must be religiously flushed!
Also the coolant flow route to the turbo can be improved on, by move from head to back of block. (Somewhere in the Tips section)
Anything you can do to reduce ambient temps in the engine room will help too, or duct in outside air to the intake.

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Tony Athens

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