I recently bought a 2000 TJ Wrangler with a 4.0L engine and manual transmission as a project. It has 172,000 miles on it. After replacing the head and some other parts under the hood, it’s running perfectly. I changed the oil using the factory-recommended 10w-30, but I noticed the oil pressure is only about 20 psi while driving and drops to 10-15 psi at idle when the engine is warm. I realize this is normal for a high-mileage engine. I’m planning to change the oil again soon and am considering using either 20w-50 or straight 40 weight to maintain better oil pressure. I know many of you have high-mileage Jeeps and was wondering which brand and weight of oil you’ve had good experiences with?
I recommend using a high-mileage engine oil, as it contains additives that help keep seals, like the rear main seal, flexible and leak-free. My preferred choice is a high-mileage 10W-30 conventional oil, which is particularly effective at preventing leaks compared to most synthetic oils. However, since conventional high-mileage oils aren’t as profitable for auto parts stores, many are discontinuing them. You can usually still find a 10W-30 conventional high-mileage oil, like Pennzoil, on Amazon or at Walmart.
Many Jeeps have racked up high mileage with low oil pressure, so go out and enjoy your Jeep. My 1998 4.0L XJ Cherokee was a work truck that received regular oil changes using whatever engine oil came in a 55-gallon drum. Now, over 290,000 miles later, the original engine doesn’t burn any oil and still has decent oil pressure. I just buy whichever 10w-40 oil is on sale.
I’ve always been into big block Chevy engines, where 100,000 miles was typically when you’d plan for a rebuild. So, seeing 174,000 miles on my Jeep 4.0 makes me a bit nervous, but you learn something new every day.
This is actually my fifth Jeep (I’ve had a '75, '79, '91, and '93 before this one), but those were all bought new, used as daily drivers with some off-road fun, and then sold for a newer model.
I used to prefer conventional oil and wasn’t a big fan of synthetic oils. However, over time, synthetic oils have proven themselves, so I use them now. I know they’re not ideal for older high-mileage engines because of how they affect older seals and gaskets. If I come across an oil specifically recommended for high-mileage engines that helps preserve older seals and gaskets, I’m willing to give it a try.
Conventional oil all the way mine has 171xxx and still doesn’t burn or leak any either.
We may be talking about two totally different type of engines and their use.
A 60’s - 70’s big block and most small blocks are good for about 100,000 miles.
I usually use 15W-40 oil meant for diesel engines in my older vehicles, or 20W-50 if that’s more convenient. I believe the diesel oil contains more zinc, similar to “high mileage” oils, but it’s more affordable.