Originally Posted By: Thebimmerfan
Regarding truck engines - have you ever driven a truck? They use to run mostly long highway trips, sometimes between countries and continents. A truck can make 10 000kms in one week, noone would change the oil weekly, because no neeed for it, oil just won't be stressed enough. For a truck 1500rpm is the upper zone or revolutions, they use to run at about 500rpm, no spirited driving there, no stop and go city driving, oil in this case doesn't see much punishment. No comparison possible between the oil in a sporty driven, dailydriver often revved up to 7000rpm and more and the one in a truck used mostly for long trips in ridiculously low rpm range.
Yes, we own three of them:
1. Has a Cummins ISB 6.7L engine
2. Has a Mercedes, not sure of the specs off the top of my head
3. Has a CAT C7 7.2L engine
All are around 250HP, they are straight-frames with 35,000lb GWVR's. They are backed with Eaton 6spd manuals. Cruise speed is around 2,200RPM IIRC, which puts them at the speed limiter (105KM/h). The RPM limit for the CAT is 2,500RPM, and will see it regularly.
OCI is 25,000Km on conventional 15w-40.
Because they are only 250HP, they are often loaded to max weight and subsequently under very high load. Use in stop-and-go in Toronto is brutal, and they can be stuck in traffic on the DVP or 401 for hours at a time in bumper-to-bumper.
As Shannow has pointed out, bearing size is much, MUCH larger, so speed is higher.
For the CAT, bore diameter is 4.25", stroke is 5". So swept area per revolution is significantly higher than your typical gasser, and these are relatively small, lighter duty diesels. Larger, OTR engines like the C13, these dimensions are even larger. The C13 has 5.12" bores and a stroke of 6.18", peak power is achieved at 2,100RPM.
The primary driver for the allowable OCI's on these engines is sump size; the volume of oil is massively higher than your typical gasser, which allows for extended drain intervals via tolerance for a higher volume of contaminants to be diluted, and this is often coupled with advanced filtration not found in the passenger car realm as well.
The C7 holds 18 litres of oil, the ISB 15L. The C13 holds 30L. This is the reason they are able to run extended OCI's.