10 hour drive after picking up JT

[mr_bots]

What RPM do these JTs run at with cruise at 80ish MPH?

~2k RPM, maybe a tad over that with 3.73s, will be a little higher with 4.10s.

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[ShadowsPapa]

I've built more than a few dozen engines over the years, if anyone wants, can provide the info supplied by the manufacturers of rings (Federal Mogul and others), bearings, etc.
but pretty much ignore what the after-market cam companies talk these days. It's rubbish, not necessary.

Bottom line is to take the vehicle out on an open road, full throttle acceleration up to about 50-55 mph in as high a gear as possible - you want to load the engine but not lug it. It's easier in a stick - because you control the load on the engine.
Slow back down, do the same acceleration in a high gear but not lugging - up to about 55-60 - repeat about 10 times.

Rings are broken in.
You want to FLEX the rings and you want high pressure on the top side of the ring, lower pressure or vacuum on the bottom side.
The rings are made so they twist, a torsional force is applied, as they work. This forces the bottom edge of the ring out to the cylinder, literally twisting the ring and forcing it out as combustion gases get behind the ring from the high cylinder pressures, forcing it out hard.
This is why they don't want lazy driving, slow sustained speed or high sustained speed - you end up GLAZING the cylinder walls.
I can dig up some pictures as well, I suspect.

In summary - they want high cylinder pressures, such as an engine being pushed but not lugged, get up to speed, do this several times
They want the rings forced out.
Engine braking actually does the opposite as you pull a strong vacuum in the cylinder and flex the other way. High vacuum like downshifting and using engine braking won't accomplish forcing rings out - it lets them float.

Again, can pull from engine books and the manufacturers' info if there's a demand for more info. I've got some books on performance engine building as well.
No, break-in procedures are the same today as they were in the 70s. Technology has changed but the parts you are breaking in really haven't. Even the machine shop I last used said pretty much the same thing. Break it in like they talked 40 years ago and it'll be just fine.
The real "break-in" as far as rings and bearings is pretty much done. It's the high points that get worn down. There will be further "wear-in" over time, typically happens up to 10,000 miles - so you may see mileage improve over that time period as well as the bearings even out further. But once you get it - the bit about ring break-in is all done with. IF it's not done in the first few miles, it's not going to help doing it now. Cylinder glazing results.

 

[TrailHiker]

The JT is a Jeep, not a freeway speed runner. While it can do 80mph, it’s sweet spot seems to be between 55-65mps. Go faster and you are wasting gas due to the extra drag of the high cab and square shape. At 65mph, my JT Sport S(8-seed auto) was hitting around 2-2.5K, depending on the gear selected, and I got 22-24 mpg in hilly mountain highway driving.
Cheers

 

[SleepyJeep]

FWIW, I can't give you any scientific or technical reasoning, but I drove from MD to OH after my truck only had 200 miles on it with the truck bed full of stuff normally and I have 7k miles on it now, got my first oil change done and no issues. Just drive like you would any other car, but I didn't go past 80mph, and it should be fine. I did get a lot of thumbs up and waves and every time you stop be prepared to have a conversation about the truck with random strangers .

 

[rafaelsmith]

FWIW, I can't give you any scientific or technical reasoning, but I drove from MD to OH after my truck only had 200 miles on it with the truck bed full of stuff normally and I have 7k miles on it now, got my first oil change done and no issues. Just drive like you would any other car, but I didn't go past 80mph, and it should be fine. I did get a lot of thumbs up and waves and every time you stop be prepared to have a conversation about the truck with random strangers .

Well my last 3 vehicles have been Wranglers.....I don't know what +80 MPH is =P

My 2dr JK feels like its gonna fall apart at around 65. I don't see myself going faster than 70-75 in the JT.

 

[TrailHiker]

The JT seems to run smooth at 70-75, I did get up to 70 on a flat bit, just to see. The issue is going to be a hit in your mpg when you go over 65-70 mph.
Cheers

 

[rafaelsmith]

The JT seems to run smooth at 70-75, I did get up to 70 on a flat bit, just to see. The issue is going to be a hit in your mpg when you go over 65-70 mph.
Cheers

I bought the wrong vehicle to be worried about MPG. I only care about smooth and reasonable. And at my age...frequent stops to get fuel is almost a necessity =P

 

[NaughtyGeek]

From the user manual:

 

[Frogwopp]

I have a rubi with 35's. As much as I try to keep 70-75, I find myself at 80. No steering issues, running just over 2k rpm, very smooth.

 

[eaglerugby04]

Like others said good luck staying at a low speed. I know my acceleration was low for my drive from Tri-City to the south side of charlotte, but I was hitting a controlled 70 for a lot of the drive back due to the flow of the traffic. Use cruse control and the engine RPMs will stay low. I am also used to being slightly softer on my acceleration just from years of a Prius letting me know I was defeating the purpose of the car if I accelerated to quickly.

 

[ShadowsPapa]

Like others said good luck staying at a low speed. I know my acceleration was low for my drive from Tri-City to the south side of charlotte, but I was hitting a controlled 70 for a lot of the drive back due to the flow of the traffic. Use cruse control and the engine RPMs will stay low. I am also used to being slightly softer on my acceleration just from years of a Prius letting me know I was defeating the purpose of the car if I accelerated to quickly.

That's rare - Prius drivers around here treat I235 like it was the Indy raceway. I've been passed and zipped around and see more Prius drivers weaving in and out than many other cars - unless it's a minivan. Those things are treated like race vans around here. Some guy pulls up with a 20 year old miniivan and is like a highschool kid in 1957 with his papa's Chevy.

Anyway, I don't let other drivers dictate MY speed. If I have a need to stay under the other traffic doing 75 and the speed limit is 65 or 70, xxxx 'em. As long as I'm in the proper lane for my speed. I'm not talking doing 50 in a 70 - I'm talking clowns doing 80 in a 70 and getting ticked at those doing 65 or 70 in a 70.
They can have their blood pressure problem.
I'm normally the ones the cops look out for on the high end of things, but at times I need to do the limit or under, let 'em blow a gasket. It's why doctors prescribe so many blood pressure meds these days. They could start for work a few minutes early - there, situation solved.

And as stated before - the RPM on these is SOOOO low at highway speeds, let it get to 7th or 8th, you'll be in the low RPM area, may need to punch it now and then to get above going too low RPM.

 

[eaglerugby04]

That's rare - Prius drivers around here treat I235 like it was the Indy raceway. I've been passed and zipped around and see more Prius drivers weaving in and out than many other cars - unless it's a minivan. Those things are treated like race vans around here. Some guy pulls up with a 20 year old miniivan and is like a highschool kid in 1957 with his papa's Chevy.

Anyway, I don't let other drivers dictate MY speed. If I have a need to stay under the other traffic doing 75 and the speed limit is 65 or 70, xxxx 'em. As long as I'm in the proper lane for my speed. I'm not talking doing 50 in a 70 - I'm talking clowns doing 80 in a 70 and getting ticked at those doing 65 or 70 in a 70.
They can have their blood pressure problem.
I'm normally the ones the cops look out for on the high end of things, but at times I need to do the limit or under, let 'em blow a gasket. It's why doctors prescribe so many blood pressure meds these days. They could start for work a few minutes early - there, situation solved.

And as stated before - the RPM on these is SOOOO low at highway speeds, let it get to 7th or 8th, you'll be in the low RPM area, may need to punch it now and then to get above going too low RPM.

Lol. They can accelerate when needed and I will pass on the freeway, but the little game on the screen is sure to let you know you are in PWR mode and burning a lot of gas. I have been called an "aggressive prius driver " before by a co-worker. Mini-vans are supprisingly fast with the truck engines they have and the smooth long wheelbases. Though when they are being driven like a racecar is is always men, at least what I have seen locally is a lot of the stay at home moms are scared of those things. They can't park them and stop at every wind in the drop off line at school.

I don't know what it is like there, but we have highways that are 55 and 60 and if you are not going 10 over somebody is riding your ass in the right lane. The cops don't even care because they are busting one of the 20 people every minute passing you going over 75 in the left lane.

 

[JP1]

Drove mine from Spirit Lake, IA to Fort Lauderdale, FL without issues.
Here was my break-in, follow this closely.
Drove from Spirit Lake to Madison, WI where the odometer read 410 miles. There I threw on the 37" tires and threw the 33s in @steffen707 's minivan.
Drove the remaining 1700 miles like I stole it.

 

[ShadowsPapa]

Drove mine from Spirit Lake, IA to Fort Lauderdale, FL without issues.
Here was my break-in, follow this closely.
Drove from Spirit Lake to Madison, WI where the odometer read 410 miles. There I threw on the 37" tires and threw the 33s in @steffen707 's minivan.
Drove the remaining 1700 miles like I stole it.

How did you fit the tires in that minivan with all the plywood in it?
Man, you should have stopped over here and sold me your 33's.

 

[JP1]

How did you fit the tires in that minivan with all the plywood in it?
Man, you should have stopped over here and sold me your 33's.

Sorry Bill, you didn't exist here on June 22, 2019.
and ya, we struggled with plywood as we put the JEEP crate in there also.

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