I have a 1987 F250 6.9 IDI automatic. While driving on any highways, so 55mph and above, the truck rides at 2500-3000 rpm. Is this normal? I feel like it should be lower but for an older diesel, I am not sure. If this is not normal, what could be causing this or what can I do to lower the RPMs?

-Tyler

 

she's got the old school 3 speed c6 auto.that's what it was like in olden times before locking torque converters and overdrives.

it's normal.for lower cruising rpms you could swap in an E40D auto or zf5 stick shift.....or slow down.....way down lol.happy Halloween.

 

With my ' 87 F250 6.9 4 speed creeper and 3.54 gears she's turning 2500 at 65 m.p.h.

 

Sounds right since both the C6 and 4 speed are both 1:1 in high gear.