I am putting a new Jasper 4.0 in my '99 Cherokee. Since most motor oils these days have very little ZDDP, I run a small amount of ZDDP additive in all my flat tappet engines - not enough to poison the cat, just enough to help with cam and lifter wear. In the new engine should I add ZDDP during the early break in cycles or will this impede proper break in? I asked my mechanic but he isn't sure.

 

Poisoning the cat is usually only an issue if you're burning alot of oil. This is going to be a hotly debated subject, just like a "which oil is best" thing. I'm under the impression that a little ZDDP isn't a bad thing, especially in a flat tappet engine, but keep in mind it's not a hotrod engine with heavy spring tension and lumpy cams. Most oils that don't have ZDDP usually have a pretty good friction modifier formula, probably with Moly in it to compensate for less zddp. I'm no expert, but I'd guess that any modern motor oil in the correct weight prescribed by Jasper would be fine. Have you asked Jasper what they recommend? And if so, what was their answer?

 

Thanks for the reply. I have not spoken with Jasper - been waiting for Monday to call. I will post what they have to say. The Cherokee's engine was not great when I bought it so I can't really tell if the ZDDP did any good. I do have a '95 Dodge Ram 5.9 Magnum that I have been supplementing with ZDDP for years. It has 280,000 on the clock and is still running strong.

 

Good idea to wait until you talk with Jasper. I've got one in our Blazer and let the Jasper certified dealer (and good friend) maintain it. Make sure it won't void the warranty.

 

Jasper says that adding a little ZDDP won't hurt but it should definitely wait until the break-in period is over. Sounds good to me.

 

ZDDP is actually RECOMMENDED for the Jeep inline six motors because of it being a flat-tappet cam. Pennzoil still has a high concentrate of ZDDP, as does Rotella. Many of the long time users on here use and recommend Rotella T6 as it's synthetic, has more detergents, and a higher concentrations of ZDDP in it. I don't know whether it's good for break-in oil or not though.

I myself have been running Pennzoil 10w30 in mine for the past 6 years and it's been really happy. No sludge, no burning, etc. Again, don't know if it's good for break-in though.

Here's some more on the topic (warning: be ready for a lot of oil talk)

https://www.bobistheoilguy.com/forum...Number=2403474

 

I've been running Valvoline Max Life 10W-30 with some ZDDP added. This is a synthetic/mineral blend. I have found that full synthetic oil causes a lot of seal leakage. When the mechanic pulled off the valve cover on my old 4.0 it was beautifully clean inside so it seems to be doing the job. I also use this oil in my '95 Dodge. The problems with my old engine were caused by the previous owner's poor maintenance. I've been nursing it along for over ten years but now I want to take some long trips and I want the assurance of a fresh engine.

 

Interesting... care to elaborate?

 

Pretty sure it has something to do with dino oil having increased seal swell in natural rubber/cork seals compared to synthetic, so if a high mileage motor gets switched over from dino > synthetic there can be leak issues. In my 4.0 engine that I care about I've run full synthetic for the last 12 years and never had a problem, so I can't testify to that personally.

 

The seal problem that I had was with my "95 Dodge 5.9 gas engine. I ran full synthetic from about 5000 miles until the seals got so bad that I had to replace virtually all of them. That was at about 230,000 miles (18 years). At that time I switched to the synthetic/mineral blend. I admit that getting over 200,000 miles and 18 years out of a set of seals isn't necessarily a bad price to pay for full synthetic performance. Most people don't keep the same truck that long. The people at Jasper are fine with using synthetic in the 4.0 after break-in, but the engine will be way out of warranty by the time the oil causes anything to leak so it won't be their problem.

 

230k miles is pretty long life out of seals... conventional or synthetic. Especially on a 318 or a 360 which are FAMOUS for leaking lol

If you used the synthetic oil in a brand new (or rebuilt) motor with new seals in it, you shouldn't have a problem with leakage. If anything, you'd have LESS chance of leakage. The major difference between synthetic and conventional oil is the size of the molecules. The molecules in Dino oil vary in size, whereas the size of the molecules in conventional are more consistent in size



Synthetic is also more "stable". It doesn't break down like conventional does. Here's a good article on the topic as well...

http://www.roadandtrack.com/car-cult...ic-oil-better/


Now, don't get me wrong.. I'm not biased towards synthetic in any way. I run conventional in my Jeep and synthetic in my wife's car. I might eventually switch to a Rotella T6 in my Jeep's motor, but I just don't see the need right now. Run what you want to run, just don't count synthetic out because you're afraid if it causing your seals to leak... if anything, it's just the opposite.

 

I too like having a litte zddp in my oil in the 4.0 motor so i use Havoline high mileage 10w30 in my wifes WJ with a little zddp additive and i use Delo 10w30 in my XJ. Both i believe are semi- synthetic.

 

Here's an informative post written by one of our own long-timers.

https://www.cherokeeforum.com/f2/rot...essing-188168/

 

Thanks. Interesting article. I appreciate all the help. The Jeep came home today and the new 4.0 is running smooth and quiet. I will be running mineral-base motor oil for the next few thousand miles so I have time to mull over synthetics. Valvoline Synthetic has kept my old Dodge running strong for a lot of years and a lot of miles so I may just stick with that - plus a wee bit of ZDDP. Thanks again.

 

Thanks for the informative article. Makes me feel a little better about the Delo I've been using and will probably bump up from 10w30 to 15w40 since I live in sub tropical south Florida. Will be switching the wifes '04 WJ to it as well.