Break-in oil

Just finished rebuilding and reinstalling my 6-258 4.2L cj engine and am not sure what type of oil to use to run it at first. I've heard regular oil isn't ideal. What should I use?

 

That is probably the most important post/ request I've seen here in some time. A question that could make or break your rebuild.

This is my input. I had a Jasper remaned in my XJ. I had a planned trip of about 300 miles, most at highway speeds. I contacted Jasper. They told me the best break in is at highway speeds with the oil that your engine rebuild recommends. And of coarse, I ran it with the oil they used. The oil they used. 5 W 30. Straight up....5 W 30. Ran that XJ with the same full synthetic for 12 of the 14 years I owned her. And never an issue. Just my input.

I've never run a motor that I rebuilt. Did rebuild a 327 years ago. But never ran it.

If any one has any first hand experience. I would definitely explore their ideas. We have some of the most experienced knowledgeable members on the Web here. Just my 2 cents. Best of luck Matt. Keep us posted.

 

Hey Matt, so I have rebuilt many motors and have broken in even more. Lucas make a great 15w-40 break in oil high in zddp. I won't get into what is in oil that makes its great as it could be a book of it's own. Shell triple t4 is a great oil as well. I could go into depth on breaking in an engine and why motor manufactures such as ford and others are now saying to run 15w-40 high in zddp all through the engines life. Long story short a flat tappet motor is the only style that really needs broken in anymore for cam reasons. Use one of the break in oils listed above and run the engine at 1800-2400 rpm for 20 minutes then drive the vehicle like normal on the high way and in town for 500 miles before changing the oil and filter. I personally run 15w-40 in my jeep all year long. Hope this helps

 

For the 1st 500 miles you should not run a synthetic. It is so slick that it won't let the rings seat effectively. Like Chris says I would run SAE 30. Also for the first 500 miles you should vary your speed/rpms so that the rings do not seat unevenly which happens if you run the same RPMs for extended periods of time i.e. you drive 50 miles to and from work on the highway and after 5 days your 500 miles are complete and is not the best break in method. By varying your RPMs the pistons rock differently at each rpm speed causing a well rounded wear pattern on the cylinder wall (seating the rings) giving a good consistent seal between the piston and cylinder wall. This is basically what SmittyJeeper is saying by driving it normally around town with some highway driving. I also like SmittyJeeper's idea of using a dedicated break in oil.

 

Thanks all for the input. I ended up finding a Royal Purple 5w-30 Break in oil from napa. I know I need to run my engine at 2500 rpm for thirty minutes on start up, and I have heard that synthetic isn't the best option but I'm glad to have the extra input. Also, as peter was saying, mine isn't a daily driver so much as a rec vehicle, so that shouldn't be a problem. Thanks for the help all.

 

That's what Jasper told me they had in my reman'ed. 5 w 30. Wasn't a synthetic. But I don't think you should have an issue with your driving intentions for the rig. Keep us posted how you make oUT.

Wouldn't hurt to post a couple pics too. We like pics. Lol.