Originally Posted by Kicker77
I've read the 4.0 l. Is based on German Diesel engines from the seventies and that the motor responds better with oil that are high in mineral count like zinc. Which is found in 5w40 synt
New environmental laws have limited Zinc dithiophosphate (ZDDP) levels to around 600ppm. Our I6 and I4 engines use flat topped lifters, meaning they need more lubrication (ZDDP is only one of the antiwear agents) than engines today. This lack of proper lubrication leads to lifter tick as the lifters begin to wear out. Its not this huge problem everyone makes it out to be, these engines can still last 200,000 miles + with regular oil changes.
If you are seriously concerned, you can buy racing oil that technically isn't meant to be ran on the streets, but will often have a much higher level of ZDDP. You can find charts that show the different levels of each ingredient in the oil through a Google search. The general consensus is these engines were made in the 70's when oil had around 1100ppm ZDDP, so that's what these engines need. Another reason why the ZDDP level is lower now is because the higher the level of ZDDP in the oil, the faster it will wear out your cats.
They do sell ZDDP concentrate in auto stores that you would add to the oil, but I personally wouldn't use it. By nearly doubling one level in the oil, it could throw others off and have some sort of negative effect on your engine. I have no tests to back this up, it just makes sense to me that we should let the oil chemists do their job.
And just for the record, its american