No that we are back from our 7k cross country trip, I decided to change the engine oil. Just wondering is there a maximum number of highway miles you should drive on an oil change? If so what is the number?

1,000 miles per gallon. I have a 7 gallon system so I go 7,000 miles between changes. I have a Detroit Diesel serviced by Detroit Diesel and that's the plan they have me follow. Oil is cheep is the way I look at it.

Cummins schedule A maintenance states every 12,000 miles. So I think you are safe. With oil analysis some people are stating they have gone up to 25,000 miles between oil changes.

Cheers
Meric

Most of you know i'm a recovering lube engineer. Some observations:

• Running with the engine at operating temps is the ideal condition for oil

• Most engine wear occurs on a cold start. Any engine should not be warmed up at idle. Wait until it's firing smoothly; if necessary wait until the air is pumped up, then go.

• Sitting unused is unkind to any engine, but especially diesels. I run mine 15 miles at least monthly. Just running at idle does more harm than good. The run heats the oil to boil off water and to renew the oil film on engine parts

• The oil change intervals on most of our engines was created before low-sulfur or ULSD. Sulfur is the nastiest of the constituents of diesel (although it also provides lubrication). Sitting idle, condensation enters the crankcase, and that water combines with sulfur to form acidic residue.

Bottom line: The recommended change intervals should probably be extended, but the engine builders aren't going to do the expensive tests on superceded engines. An additional reason intervals can be safely extended is the more robust additive of contemporary oils.

• Nevertheless, "Oil's cheaper than metal!"