As I understand it, our Jeep CRD's require a Synthetic oil

Yes, conventional oils don't have the shear performance so will break down much quicker especially in a turbo charged engine.

I've been running a 5W-30 group IV basestock (PAO) synthetic diesel oil, summer and winter, in my CRD since we've had it, almost 7 years and 85,000 miles. It's a fact, many so called synthetics are only highly refined petroleum....you can tell by the price.

Like all other oil manufacturers. But remember, there are higher quality basestocks and additive packages available...but they cost more. I'm not going to get into another oil discussion here. You run your junk I'll run mine. Let me see you go 2 years and 21-22k miles between oil changes with oil analysis results backing this up and the results saying oil is good for continued use, resample in 7000 miles or 125 hours.

Why would you run 15W-40 in the summer if there is 5W-40 available. They are going to be the same weight at operating temperature with the 5W having the advantage at start up.

Why would you run 15W-40 in the summer if there is 5W-40 available. They are going to be the same weight at operating temperature with the 5W having the advantage at start up.

Tough one to answer and I certainly am no expert on oil viscosity. I like some others on this list base my opinions on experience from 40+ years of working on motors mostly gas burners. I have rebuilt gas engines that ran lower weight and / or poor quality oil and like the picture showed in one of the posts the insides were gunked up and everything completely worn out including the block.

I have always run 20w-50 Castor Oil in all of my gas engines and never experienced any engine or oil related problems. I also change oil every 5000 miles or less regardless of what the manufacture recommends. I have worked on many VW air cooled engines in the past that used 20w-50 and you could not find a speck of dirt or sludge in them and they ran at a much higher temperature than any water cooled engine. Back in my drag racing days, we always ran 50 weight oil to handle the high horsepower and pressure loading of the bearings.

If they made a 20w-50 full synthetic for diesels, I would use it. If you buy into the low weight propaganda; it was only done to increase fuel mileage to meet government millage requirements and certainly not to protect anyone's engines. I would much rather have the higher viscosity oil weight at start-up than a few more miles per gallon anyday! Here in the south, it may be 90 to 100 degrees at start-up and only gets worse. Think about it, up until a few years ago, no one had even heard of a 0w- whatever weight oil.

I have found two full synthetic diesel 15w-40 weight oils available in retail stores, one is Royal Purple and the other is Lucas Oil and they are not that much different in price. I will be using one of them in my CRD starting this weekend...

thanks for all the good discussion on oil. Information helps us all make better decisions.

I agree and that would be a good choice if it were not for the fact that the manual states it requires a synthetic oil. Is there something in the motor that requires the synthetic oil?

From the manual:
"Only use synthetic engine oils meeting the API Categories SL/CF and Chrysler Material Standard MS-10725. Those engine oils not meeting the viscosity and API Quality and MS-10725 requirements should not be used."

Is there a reason for this