so to do it right for (ALL?) 04 - 06 TJs with 4.0 I6L :
- get one of those rare new 04-06 CPS assemblies
- get one pre 04 CPS assembly (new? rare?)
put the pre 04 gear on the 04-06 assembly
... and if you are unlucky : fix your cam shaft as well.
AND : find a solution for the low ZDDP in the standard engine oils.
I've done allot of research on this issue and this is streamline version of my recommendations.
Pull your CPS assembly and replace then gear. While you have the gear off pull the shaft out and inspect it and the bushing for excessive wear and runout.
If your CPS assembly shaft doesn't have the runout or visible wear on the shaft then put a replacement gear on it and reinstall and you will be fine.
Now the issue of the gear. When it comes to finding a gear you have a bunch of choices.
You can buy a new one from Crown manufacturing (I note the part number in a earlier post), you can pull one off the CPS assembly from a 99-04, or you can get a gear off a pre-99 TJ.
Now if your CPS has the "laughing monkey" syndrome you need to hunt down a new CPS assembly. As far as its gear, gears are cheap, easy to find and easy to swap so its not worth risking it. Get a replacement gear and swap it out.
Now before you install the new CPS you need to get a good bright flashlight or better yet one of those flexible inspection cameras and give the camshaft gear a good inspection. What you’re looking for is striations, worn spots and marring or chipping of the edges of the camshafts worm gear. If the camshaft looks good then install your CPS assembly and your done.
As far as the issue of ZDDP oil you have three choices.
For conventional oil in summer months run 15W-40 Delo LE oil which has 1300ppm of ZDDP.
In the winter months you can run Mobil One 5W-40 Turbo Diesel Truck oil which also has 1300PPM of ZDDP. Or if you want to you can use a ZDDP additive.
My recommendation is to run the 15W-40 year round if you’re in the warm southern part of the states and the 5W-40 if you’re in the northern states and don’t waste your time with the ZDDP additives.
Also note that all diesel oils are NOT equal when it comes to ZDDP. Shell Rotella, Mobile Delvac and several others have also reduced their ZDDP levels to the 700-800PPM level.
As far as the weight of the oil I know several guys with CJ’s and TJ’s that have run the 15W-40 with 250-300,000 miles with zero problems.
I know someone is going to ask what about the manufactures recommendations? In a nutshell the government says a car company’s fleet has to have a certain average of miles per gallon fuel efficiency.
So the car makers realized that they can specify thinner weight oil because on paper in a laboratory environment it yields 1-2mpg more which when applied to 10-15 car models greatly boost their café average.
If you want proof of this look at Ford. There are several vehicles that they make both here and in Europe. The vehicles they make for sale here specify 5W-20 but the same vehicle same engine that’s being sold in Europe Ford is specifying 10W-30.