Caterpllar C9 6L versus Cummins QSB5.9

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driver0606

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Hello,

Similar boats. One is 2010 with Caterpillar C9 6L 575 hp engines with 600 hours, the other 2013bwith Cummins QSB 5.9 480 hp with 400 hours but has not run for the last 2 years.

I do not intend to run the engines too hard and do not need the extra horse power. There seems to be more Caterpillar agents in my area.

Which would you choose and why, please?
 
The engine guru on here Latestarter1 says the QSB is the best marine engine. I had Cats (7.4 dTI’s) in my Azimut, and was very happy with them. Properly maintained, either engine will serve you well.
 
Service history @ this age .
Are they both common rails? Thinking the none CR one ( if there is one ) might throw less hissy fits , expensive injector hissy fits .

Look at the anodic protection .Yes according the each manufacturer they will claim a all singing and dancing system , but how easy is that tune to follow by none franchised techs or competent DIY ers in the field ?

On the same vein ^^^ I understand CATs of that generation consider the CAC s @ 7 years a throwaway part .
Dissimilar metals / air drying anodes / anodes not checked - etc = water gets sucked in or dribbles into the cylinders = kaboom ? .This should surface in the service history check .

Finally what are they in ?
Power / weight ratio stuff. Motors “on the edge “.Toss in seasonal fouling = elevated EGT s not good .
Had one indeed got load and EGT instrumentation ? If so the motors might have been used sympathetically?,
ER work around access - the position of the tanks .= lateral tanks tend to cramp outboard access = stuff neglected.


Its a multifaceted, multifactorial answer that cannot be given on a straight “ is A better than B “ without more info I am afraid .

eg if the prop pitch has been arsed around with .Or one of the boats never reaches rated rpm at WOT .

So for me a simple sea trial will swing it because I doubt very much both boats will reach rated rpm .
Buy the one that does ,Walk away if neither.

The one that’s been stud for 2 yrs with the same anodes + fluids could be a crock of 8hit .
Rusty exhaust valves and gummed valve guides , gummed turbo bearings = never get near WOT rates rpm .
 
Last edited:
Bouba said:
I agree with Porto, it’s not just the engines. What are the fuel tanks made of?
Click to expand...
No it’s more where they located over the material and how they are insulated from flexing .

Don‘ t get hung up on the materials per se .
This boat RHS HT 58 sports cruiser “ Kubang “ lost August having its SSteel day tank removed , sent away to Genoa for a busted weld that started to leak .
I saw it on the jetty the day it came out .
A few days previously we could smell that some one on the fuel jetty has spilt some smell and see the rainbow sheen on the water .Prob with that diagnosis is we are 500 M + away .
Turned out this guys bilge pump responding to the ER filling up .
That boat has 3 tanks .Two huge and a smaller day tank the size of a large suitcase.Fortunately it fitted through the normal ER hatch .How ever with the best precautions diesel got into the teak everywhere in a Sod’s law way .

They just re welded it up , it was a seem pin hole .

1C10FEE3-D99D-41DC-9F45-B26ADAFA7BBD.jpeg
SSteel is more brittle and less flexible .Aside the welds I bet Uri Geller couldn’t snap a AL spoon between his fingers like SS :)
 
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