I am looking at buying a 1997 F250 7.3 auto with 130k miles. I need this truck to last for at least the next 5 years. How high of mileage is too high, I've heard that diesels last longer due to the low revs they turn but, I need it to last for a while. Thanks.

 

Diesels might last longer because of the lower revs, but primarily, their longevity is attributed to the closer manufacuring tolerances when manufactured, plus the strength of the components. The Powerstroke engine is engineered for 300K miles, more if maintained properly. I wouldn't bat an eye at 130K miles.

 

If the above engine has been well maintained and properly operated it could very well have and additional 150,000 miles, or more, left in it. If it has been improperly maintained and/or improperly operated it could EASILY be SHOT right now. Just because it's a diesel does not mean it will always last a long time. Diesels do produce their power at a lower average RPM, but they also operate at higher cylinder pressures and bearing loads. Cold starts and prolonged ideling are harder on a diesel than on a gasoline engine. Diesels also normally produce more soot as a by-product of combustion and thus through normal blowby, contaminate the crankcase oil more than a gasoline engine, so diesels normaly are more critical to regular oil and filter changes than a gasoline engine. Diesels also require a higher detergent oil to keep them internaly clean than gasoline engines. Diesels are excellent for long, continuous steady temperature operation. They are very poorly suited for large numbers of cold starts and short (say, under 10-minute) trips. These operational traits can have a MAJOR effect on a diesel's life expectancy.
About the best test to see where a diesel engine stands as far as condition is a fully warmed and full load blowby test. This usually requires a chassis dynomometer and measuring instruments. The other, and less important test would be oil pressure. It should have at LEAST 30-psi at 1000 RPM with the oil HOT. What it has at higher RPM is much less important than at 1000 RPM. Quick starting and a smooth idle are also good indications of healthy injectors. The most expensive area of any engine to fix is the "blow by" area, which means pistons and rings and cylinders. That is why blow by is the most crucial used engine criteria.

BobJonesSpecial

 

I wouldn't say the manufacturing tolerances are any better or worse than Ford's gasoline engines. They manufacture the gasoline engines very carefully also. The diesel does however have stronger individual components, but these components have much higher loads due to higher compression and higher cylinder pressures. The diesel's longer life is usually due to lower average RPM.
The large commercial diesels found in over-the-road semi's have some extreme quality features that are not found in a pickup truck diesel.

BobJonesSpecial