Intrepidjeep, I was merely stating that synthetic oil for that motor is just not cost effective. If you add up the total money spent per quart for synthetic versus regular oil over the life of the engine, you might be surprised at the end result. For instance, let's assume that you will be keeping the vehicle for 300,000 miles and changing the oil every 3,000 miles. That would be a major feat for a Jeep vehicle, but bear with me. A regular quart of Mobil oil goes for around $1.30 at my local auto parts store, whereas a quart of synthetic Mobil 1 goes for $4.99 per quart. We'll also assume you'll be buying 7 quarts of oil for each oil change. I'm guessing for that amount as I've never had a 6 cylinder Jeep. For the duration of 300,000 miles you'll change the oil 100 times, whew! In the end you'll have spent approximately $910.00 (excluding oil filters) on Dino oil. The synthetic will cost $3,493.00 (once again excluding oil filters). The Dino oil is $2,583.00 cheaper than synthetic over the course of 300,000 miles.
At 300,000 miles, the engine on the Jeep will be dead. Synthetic or not. The $2,583.00 can go towards a new engine, or a new Jeep! I realize that no one would actually put the $25.83 into a savings account every oil change, but I think you might see where I'm coming from.
I'm not trying to shoot down everything you said about the benefits of synthetic oil either. Synthetic oil IS a superior lubricant to Dino oil for ALL engines. I just wouldn't put it into an engine that doesn't cost a lot of money to replace, such as the 4 liter inline 6. I agree with most all of what you said, except for lengthening the oil change intervals. The oil (synthetic or not) will still get a build up of impurities in it over the course of it's life. Changing it at shorter intervals keeps the engine from getting a build up of sludge.
2003 Grand Cherokee Overland