I am considering the purchase of a 1991 montero sport for my son. it has 177,000 miles but runs and sounds fantastic. whats your opinion?

I would not see why you couldn't take this vehicle to 250k miles if it is in good condition and the timing belt has been replaced. Compression numbers should be within 10-20 psi of each other, with any glaring differences indicating cause for concern. Exact compression numbers should be in the Haynes manual for this vehicle, which I would suggest buying just to give you an idea of what specs should be on it so you can compare them to the vehicle. If it were me, I'd look for something lower mileage of the same vintage, just because you likely may be looking at repairs before the loan is settled.

I agree that the first thing you should do is insure that the timing belt has been changed. better yet have it changed to be on the safe side. These vehicles are tough. They havent been given their due by Mitsubishi as they out perform there competition. When buying a car of this age do your due dillegence. Your son will get may miless of great perforemance.

I wouldn't worry to much about mileage on these as if it has been looked after they will run forever I don't know a lot about this motor so that's about all I can say sorry.