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Cummins ISC Engine

Discussion in 'Truck Talk' started by guest, Jan 13, 2000.

  1. guest

    guest Guest

    Am thinking of going with a Cummins ISC 300 on my next truck (D-Unit, FL70 frame). Heck, the 15,000 oil drain interval alone makes it an easy choice over my CAT 3126-B (8,000 drain recommendation).

    You Cummins owners/drivers out there, any words of advice, horror stories, things to look out for, spec-ing advice, etc.?

    I know there were some major problems with fuel lines and fuel pumps in '98, but have been told (and you all know how that goes) that those problems have all been fixed. What say ye???

    Thanks for your time and advice...

    Rams Fan
  2. guest

    guest Guest

    Cummins ISC Engine -- Comments Please

    I have a isc 285. they replaced some lines on the back of the fuel pump the day after i got it. Said it was a recall. Only other problem I have had on engine was a leaking fuel line on # 1 cylinder, and the elec. lift pump started leaking. got both fixed under warrenty and all has been ok since then. There is 114500 mi. on it and I get just over 10 mpg.
  3. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    i just to have a truck with the 5.9 cummings now i have a 250 cat and much hapier with it thx.
  4. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    Have you considered converting a class 8 tractor? I have a 96 volvo, recomended pm is 22k, i do it at 15 to 18k. You spend less monet and gat a motor that will last well over a million miles and get ALOT more room and comfort. My fuel milage is running 8.5 to 9, and i can carry 26k if needed, this has gotten me out of "dead areas" hauling ltl for LEA sister co. more than once. If you need more info contact me Doodle LEA unit4862.. See my truck in cool trucks on this website
  5. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    What is your cruise RPM, axle ratio and tire size? 10 MPG seems pretty good!

    I've heard and read 1650 RPM is the best mix for power and economy in the ISC (optimal cruise RPM). You agree? Recommendation is to lug it down to 1350 to 1300 RPM before grabbing a gear when pulling a grade for best economy (max torque @ 1300). Your thoughts on the ISC's torque curve and shift points?

    Do you feel you'd get better or worse milage with the higher HP 300 or 315 model?


    Rams Fan
  6. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    I have a c series 225 HP engine,have 360000 miles on it and have gone thru 2 fuel pumps,one totally replaced under warranty (they claim it costs $4700) and that one also went out after 100,000 miles so they gave the pump under warranty but did charge about $900 for labor.other then that they seem to be ok.I get 11.5 mpg at about 62-3 mph.
  7. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please


    Anything over 11 MPG shows you are a very good/smart driver!

    Thanks for the reply.
  8. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    axle ratio is 3.21. tires are 22.5. Your rpm suggestions are right about where I run it. Pulls hills real nice. I have been all over Caliifornia and the rest of the western states and had no trouble on the hills.
  9. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    FYI...The ISC 300 and 315 are the is advertised HP the other peak HP. Some dealers use the higher # for advertising purposes. I'd recommend a Super 10 or trans with a .74 OD and a 3.90 rear end. Great for cruising and good mileage.
  10. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please


    Thanks! I was debating between the 3.90 and the 3.70. Considering the torque curve on the engine, the fact that as a D-Unit my average freight weight is usually only about 5-6,000 lbs (rarely over 10k) and that I'm empty/deadhead about 33% of the time, I figured to improve my overall MPG even further with the 3.70 rear-end. I am hoping, however, that the taller ratio can be supported under load by the an ISC at 300 HP (which, I believe it can).

    Your thoughts?

    Mr. M
  11. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    I have a 99 kw with a 300 and 10 speed eaton-fuller and I
    havent seen a cat yet that can run up mountains with me.
  12. guest

    guest Guest

    RE: Cummins ISC Engine -- Comments Please

    We're driving a 99 FL 70 w/ 300 HP ISC coupled to 10 spd Eaton Auto shift. Do P.M.'s every 10-11k. Get 10 - 11.5 MPG. Unsure of axle ratio. Using 22.5 lo-pros. Truck now has over 130 k miles with not a single problem with drivetrain. Never need to downshift until over 8k lbs and in excess of 7-8% grade, then only one gear. We can run 70 MPH on any interstate hill east of the Miss. in top gear up to 10k load. With engine brake, you never touch the service brakes, either. Would highly recommend this engine.
  13. rrockfordd

    rrockfordd New Recruit

    10 year old thread and i want to revive it in hopes somebody will find it beneficial.

    -2001 Kenworth T300 26 ft box

    -cummins ISC 260.

    -eaton fuller 6 speed with .78(?) O.D.

    Rear end:
    -4.33 rear end.

    Fuel additive:

    Tires (new):
    -bridgestone M720 (drive)

    -low profile box (u.s. mail)

    @ 62-65mph (no cruise control.. yet) i get 12.55 mpg minimum. with new air filter installed today i expect to get close to 13mpg at those speeds. well see in a few days..

    250 miles empty and 250 miles with about 3k lbs. (i dont think weight has much effect on mpg unless its a lot of stop and go driving. I stop about 6-7 times a day. no traffic.)

    aerodynamics to come:

    -custom fitted side skirts
    -boat-tail (2nd quarter 2011)
    -cab side skirt (where cab meets box body)
    -Custom low front bumper
    -custom made bucket light covers

    upgrades/improvements to come:

    -Aero turbine 4040XL muffler to replace stack
    -long overdue valve and timing adjustment (oops!)
    -espar hydronic 5 coolant heater (anyone in boston want to install this?)
    -OPS1 filter (anyone in boston want to install this also? =)
    - different rear-end gears
    -and yes, this includes topping off tire pressure (im lazy)
    Last edited: Nov 11, 2010
  14. sewmun

    sewmun Rookie Expediter

    I have a FL70 w/a 225 hp engine & a tall box & get 11 on the road.Mine also has the 6 speed direct gear,it came w/a 4.11 gear & I changed it to 3.42.

    I have cruise but usually take it off iwhen I'm in the hills .
  15. rrockfordd

    rrockfordd New Recruit

    11 mpg is pretty darn good, im assuming you also do a bit of off highway driving because i would expect you to get better mpg.

    i changed the air filter and i added cruise control. with cruise set to 63 mph i got 12.90 mpg even with vermonts mountains and 4 additional rest area stops today.

    i cant wait to get my valves adjusted and slap on that aero turbing 4040xl muffler next week to see what i get for mpg
  16. greg334

    greg334 New Recruit

    If you got 12.9, leave it alone.

    The overhead may mess the mileage up.

    Timing adjustment?
  17. rrockfordd

    rrockfordd New Recruit

    valve adjustment and engine timing.

    what do you mean by this: "The overhead may mess the mileage up."?
  18. greg334

    greg334 New Recruit

    Just what I said.

    Having an overhead done can have a negative affect on your mileage, somewhat messing with the equilibrium of the engine. However the change in the exhaust may help but not enough to justify the cost.

    The Turbo is the restriction on the engine more than the rest of the exhaust system and getting one that breaths a bit better may help more.

    Getting 12 plus is a good thing, messing with a good thing can be a bad thing.


    You should have a CAPS FI and if so, don't mess with the timing unless there was some work done to the system, the computer will take care of that.

    Progressive shifting seemed to help me more than anything else which falls into the driver's habits category. Also learning where the volumetric efficiency sits with my drive train helped out a lot - which is 62 mph.
  19. rrockfordd

    rrockfordd New Recruit

    my confusion was with the term "overhead". i didnt know what it meant, but i understand now.

    as far as the timing goes, i dont know much about engines, but the woman at cummins service center said the valves and timing will be done. im guessing this means that over time the timing of the engine gets out of tune and this will adjust it back to where it should be (factory).

    i have greasy soot (diesel apparently) trailing across the box body. i have no visible black smoke on start up and no visible black smoke while i drive at any rpm or quick acceleration. i am assuming the valves are off timing and that is why the engine is not getting a complete burn.
  20. greg334

    greg334 New Recruit

    Well np, the issue with the soot is caused by a number of things.

    I would first look at driver habits. "lugging" the engine under load (meaning low below 1100) will cause it and you won't see it.

    The main thing is your mileage. If it is good, then things are alright with the timing and overhead. If the mileage drops, then an overhead will be needed.

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