I have never had a Cummins rebuilt, but I had a Detroit 60 rebuilt inframe for $7300 and I had a 425 Cat that I was shopping around and couldnt find anyone to do it for less than $11000. I sold that truck to the junk man. I would say the Cummins would be closer to the $7300 but probably not cheaper, parts for the Detroit usually are less expensive.

Probably around $10,000 would be a good estimate. I would use Cummins brand parts instead of after-market, for the pistons and liners especially.

I know a guy who rebuilt a Cummins 500 about a year or two ago and I believe he paid about $8,400. But it depends on what you do. I would count on $10,000. If you are going to rebuild the engine, I would replace everything, such as the turbo.

What about a reconditioned engine? We have one of them in one of our trucks and it's better than a new engine.

A reconditioned engine would probably have you down for a shorter time period than doing an in-frame.

I owned a 350 BC 2 for 18 years and inframed it once and had to put a cam in it earlier this year. I've since sold the truck, But it was running very good.

What I would advise is to have someone who knows this engine check it out. You may just need the engine tuned up, Or you might have a bad injector, fuel pump, etc.

If you've lost power suddenly it might be something simple.

If you're due for an oil change get it analyzed if you can. If you change it yourself look at it close and smell it for diesel contamination or signs of coolant.
Always watch it at the dip stick too, by feel and smell for diesel contamination. Or say, it used to use a gallon of oil a week and all of a sudden it's not. It may be diesel getting into the oil from a bad injector or ?