ISM cummins or 60 series detroit?
I currently have a 2 trucks. My old truck is a 1999 freightliner century with an ISM cummins@370hp. I have no problem getting over 8mpg and often 9mpg in my operation. Tanker work, 80,000lbs 50% and 30,000lbs 50%. I just picked up a 2003 freightliner columbia with a series 60 detroit@ 430hp. I'm frustrated with this truck because I cant get better than 6.5mpg with it. I'm wondering if I should just get rid of this truck. The only difference in these two trucks are the rears and transmissions. The 99 has 2:79 with a 10 spd direct and the 03 has 3:73 with a 10 speed overdrive. They both run about 59-60 at 1400RPM and are driven exactly the same way. I'm going to do some trouble shooting on this detroit. Check charge air cooler, run overhead, and dyno it. My biggest question would be can I ever get this detroit to get the same or better mpg as my ISM Cummins. My ISM has close to a million miles and still gets great fuel economy and doesn't use oil and has never had a mechanical issue. This ISM is a really nice motor, nothing like the older M11. Just wondering if the detroit will ever live up to the ISM in my operation.
Is this a good question?