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TJ Engine Replacement Project

wct097

NPD Club President 2021-2022
Staff member
Super Moderator
VIP
110K is just barely broken in. 300K on mine right now. M1 10-40 and Motorcraft FL1A filters.
This is incorrect. You're living on borrowed time. Oil changes and maintenance history don't mean squat for the common 4.0 problem of breaking piston skirts. I've seen it at 150k and always below 300k. Personally seen it on four engines, two of which I personally maintained using M1 oil.

4.0 going over 250k without breaking pistons is likely a rarity and possibly more related to fuel quality and flat terrain than oil.
 

DieselSJ

Staff member
VIP
This is incorrect. You're living on borrowed time. Oil changes and maintenance history don't mean squat for the common 4.0 problem of breaking piston skirts. I've seen it at 150k and always below 300k. Personally seen it on four engines, two of which I personally maintained using M1 oil.

4.0 going over 250k without breaking pistons is likely a rarity and possibly more related to fuel quality and flat terrain than oil.
Mine wasn't treated nicely. Twice it went from Vegas to Reno with barely touching pavement. It did a lot of miles in support of the race team.
 

wct097

NPD Club President 2021-2022
Staff member
Super Moderator
VIP
Mine wasn't treated nicely. Twice it went from Vegas to Reno with barely touching pavement. It did a lot of miles in support of the race team.
Going to go with luck then. Maybe highway miles at speed on flat terrain are better because it reduces pinging / piston slap / leading cause for 4.0 failure.
 

DieselSJ

Staff member
VIP
Going to go with luck then. Maybe highway miles at speed on flat terrain are better because it reduces pinging / piston slap / leading cause for 4.0 failure.
Thought I lost a skirt last week when it started knocking pretty bad. Actually turned out that the dizzy shaft got so sloppy that the rotor was hitting the terminals inside the cap.
 

John

Transplant
VIP
This is incorrect. You're living on borrowed time. Oil changes and maintenance history don't mean squat for the common 4.0 problem of breaking piston skirts. I've seen it at 150k and always below 300k. Personally seen it on four engines, two of which I personally maintained using M1 oil.

4.0 going over 250k without breaking pistons is likely a rarity and possibly more related to fuel quality and flat terrain than oil.
I had one go at 60k miles.
 
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