Doogluus88

So I have a 94 xj with the 4.0 and about 165,xxx miles on her. All things considered she runs pretty well for her age. So my question is about my oil change intervals....

For the last 2 years I've been working very close to home (Like, I probably do less than 7 miles for a round trip to work and home each day). This coupled with the fact I drive my wife's old bonneville about half the time (because it's AC still works) means I rack up very few miles on my xj. If I go with the old 3000 mile oil change interval it would take absolutely forever to do that many miles. So how often should I change it? Every 3000, or just keep an eye on the color and viscosity?

P.S. I typically run Pennzoil 10w-40 High mileage, and have for years. I've switched to the NAPA filters too thanks to this forum. Also thinking about switching to Rotella T6.... Any thoughts? Thanks in advance guys!!

Bustedback

I change mine every six thousand miles or every six months, which ever comes first. My commute is only seven miles both ways too, but I do some long distance drives on the weekends. I usually use 15w-40 and a Wix filter, but I just changed my oil last weekend and used the Walmart brand 10w-40. No reason, just thought I would give it try. No issues so far.

BlueRidgeMark

Those short drives are MURDER on an engine. Don't change by mileage, change by time, if you can't change your driving habits.

Short drives don't get the engine warm enough to drive out the moisture that is created by the burning of gasoline.

You need to get the thing out and warm it up, regularly.

Doogluus88

I do always make sure it gets to operating temp even on short drives to work by letting it idle for a while if I can. All that being said, how long does it take the engine to burn off all that moisture?

Bustedback

About twenty minutes of driving gets the engine up to full operating temperature.

BlueRidgeMark

Yes, but you need some time at operating temperature to drive off the moisture.

It's not just temperature, it's time as well.

From what I've read, you need at least 30 minutes to avoid building up moisture. Doing a bunch of short runs are going to build it up, so you'll need a longer run, say, an hour or more, to get things cleaned up.

If I had that kind of commute, I'd make sure to give it at least a full hour run each weekend, and change the oil at least every 3 months.


Here's some interesting info from GM. It's about storage, but the same principles apply.

extrashaky

Are you sure the recommendation for your year is 3000 miles? The factory interval for mine was 5000. The intervals have lengthened as oils have gotten better, and the old standard of 3000 miles can actually be bad in some situations. With the improvements in motor oil, I'm not sure I would do 3000 mile oil changes even in an older car for which they were recommended.

Regarding condensation, Blackstone Labs says that running it 20 minutes is enough to burn it off. But the engine needs to run longer than that to stay healthy, because the oil is doing other things once it gets up to temp.

In one sense, a car motor is a big air pump, sucking air in and pumping air out. When it stops, there is air trapped inside. Hot air can hold more moisture than cold air, so as the air inside the engine cools, moisture begins to condense out of it like dew on the inner surfaces of the engine. That moisture, along with unspent fuel, causes corrosion.

Pretty much all motor oil contains a detergent package to help handle the moisture and prevent corrosion. The detergent molecules chemically bond to oil on one end and water on the other to hold the water in solution and prevent it from doing as much damage. As the engine heats up, the water boils out and is passed out through the exhaust. If you didn't have the detergent in there, the moisture would emulsify in the oil and would cause more wear during the warm up phase.

On the other hand, detergent also damages the sacrificial layer of zinc and phosphorous that protects the engine surfaces from wear. The oil contains these compounds and lays them down again during normal engine operation. There's a continuous process of wear and replenish as the zinc in the oil is cooked onto the surfaces while at running temp. SAE and the oil companies have made a lot of strides in the last couple of decades in getting the balance between detergent, lubricant and replenishing compounds just right.

When you only drive short distances, you only give the detergent a chance to work to get rid of moisture and damage the sacrificial layer of zinc. The oil doesn't get a chance to lay down any new material. So the engine wears faster. It's not nearly as critical an issue as it was 20 years ago, however.

The other issue you have to deal with is volatility. Oil is most volatile when it's new, when certain compounds are being cooked off. These compounds become soot or gunk. So you normally wouldn't want to change your oil at 1000 mile intervals, for instance, because you would always be depositing junk from the oil into the system.

With all that in mind: What you want to do, and what most manufacturers' oil change intervals are designed to do, is to keep the oil in the engine past the volatile stage but get rid of it before the detergent and zinc additive package are spent. Too short and you gunk up your engine. Too long and you have increased wear. You want the oil in your engine to be in its sweet spot for lubrication and wear protection as much as possible.

The big issue with your low miles is that you may be using up your detergents in fewer miles because so many of the miles are driven with moisture in the motor. What I would do if I were you is to send off an oil sample to Blackstone Labs for analysis at your next oil change and pay the extra for a TBN to see how the additive package is holding up. The basic test is $25, the TBN is an extra $10, and they'll send you the test kit for free if you go to their website and request it. Include a note explaining your situation and let them know you're interested in the ideal time interval for oil changes as well as mileage interval. They'll send you an oil report via email, and they're good about answering additional questions via email once you get that report.

I get an oil analysis at every oil change for all my vehicles, just for the peace of mind that comes from monitoring how my engines are doing. Your situation seems tailor-made for their service.

What I would also do if I were you is try to drive the Jeep for a while every now and then to give the zinc in the oil a chance to work. Even if the test says the oil is okay, driving it 7 minutes is not enough, and idling for 20 before the drive is not enough because the engine needs to be working through its entire power range for the process to work properly. Take the long way home every once in a while.

Bustedback

Good information

Doogluus88

Wow! Thanks so much everybody for the great info and advice! This is why I love this forum and the jeep community!

Anyone have any thoughts on me making the switch to rotella t6?

extrashaky

There are more thoughts on that than you'd ever want to read in this thread:

https://www.cherokeeforum.com/f2/rot...essing-188168/

Overall consensus seems to be that it's recommended. I'm running a different oil in my stroker for the extra zinc, but if I were running a stock motor I would probably switch over to T6 after reading Salad's exhaustive analysis.