My dads old truck got 12 mpg at the best. Has had everything except the frame replaced. Transmission rebuilt 3 times, motor rebuilt once, replaced once and new heads and turbo, injection pump new guts in the front end. ENOUGH SAID!!!!!!

 

From what I understand, it can be a concern with all diesels, but in the mid 90's they started adding the SCA's in at the factory. The other diesels probably have thicker cylinder walls so it would take longer for it to happen. Newer diesels run much lower compression as well(18.5:1 VS 22.5:1) so that probably helps too.

A good rule of thumb for the IDI's is the weakest of the 7.3 blocks will cavitate around 150k miles. If it shows no signs of coolant loss into the motor, I would get the SCA's in there ASAP and you should be good for a long time. The SCA's cant reverse cavitation but they can stop it from happening if it hasn't already.

I had to replace most of my cooling system shortly after getting my truck. I refilled the whole system with Fleet Guard, a brand of antifreeze that has the SCA's already in it. I use a test strip in the fall and in the spring to check the SCA level and so far haven't needed to add any more additives. The strips are cheap, $1.50 each so I figure it's cheap insurance to make sure my truck will last a long time.

 

Agreed on checkin on the cavitation.

I think the IDI's are excellent engines. They arent the most powerful, but they last forever if taken care of, and 162k miles is very low.

About fuel mileage, to the guy that got 12mpg, I dont know how. My pawpaw had a 93 7.3 turbo IDI and he got about 23 mpg highway, dont know how, but he did. Seems like they either get really bad or really good.

 

Both my IDI's get around 18mpg, the 86 does it more consistently though since it doesn't have a turbo. When you have a turbo, you really like to hear it spool which involves a heavier foot.