When I bought the last group of trucks for my business, I got the Peterbilt dealer to go over the overheads and to put them all on the dyno. They did this in part because I wanted to make sure as used trucks that they were up to spec's. The other reason was to get the 1 yr 100,000 mile warranty from Detroit. The trucks had just over 500,000 miles on them. All had some blow by. One of the four had some issues when they ran the overhead and they had to spend about $1800.00 to get it right. One when it was dyno'd was lacking horsepower and they had to take care of that. So it is fair to ask the owner to have it checked but they may tell you to pay for it. Some of my trucks with 700,000 miles on them have a lot of blow by but I am still running them. One of them under 200,000 has visible blow by. Blow by itself is not a big deal unless it is enough to be dumping oil all over the place. Look good under the truck at he places that are not easy to steam clean and see if there is alot of oily debis and that will tell you if you should have it checked out. We used to have some older detroit engines that leaked about a gallon of oil a day thru the blow by and that was considered average!!
Wick
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