sreilly77

Hey everyone:

I have a 1998 Jeep Grand Cherokee Laredo with the 4.0L I6 and 170,000 miles on it. I have been considering switching to full synthetic oil. It is due for an oil change and I need some input on switching to synthetic. Is it good to switch with an engine with such high mileage? How often do you change the oil? Are there specific oil filters that I need to buy? These are just some questions I have, but any extra information would be great. It doesn't burn or leak any oil. The main reason that I have been thinking about switching is because I drive this Jeep on the highway a lot. It runs like a champ and I very rarely have problems with it (knock on wood). So any input on what anyone thinks about switching to synthetic oil would be great. Thanks a lot!

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Sean

toddman67

I personally would stick with whats working for you now. Changing oils at this point might cause some adverse affects such as leaks and wear. If you're running mostly highway miles, you may extend the change interval a little.
In this business when things are working and going smoothly, It is hard to make changes that may cause more harm than good. Just be consistant with the products that you use.

As always, this is just my opinion.

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fredjacksonsan

IMO synthetic is better than conventional oil; while regular oil is very very good these days, synthetic allows higher mpg (verified on several vehicles I own/owned) and runs cooler than conventional oil, is more resistant to heat and supposedly lubricates better.

toddman67's right, you can get some leakage when switching over. His point that whatever you are using should continue to work is a good one ...the most important thing is to change your oil at regular intervals.

The reason that switching causes leaks is that conventional oil usually forms a little "crust" or deposits around the seals and other spots; and over time this crust ends up actually doing the sealing. When you switch to synthetic, the synthetic reduces or erodes this deposit, and as it does you get some leakage (some stories I've heard say a lot, some say a little). Once the deposit is gone, then the seal softens up and does its job again and the leak usually goes away. (Check out the forums at this site for more about switching and oil in general...there's more info there than you'll probably want...)

While I can't speak for your engine at 170K, I can say that in 2005 I bought a 2000 GC with 105K miles on it and switched to synthetic. I got some weeping around the seals, but not enough to make a puddle on the ground, just enough to make it look wet. I had no leaks before I switched. After a few thousand miles, the seepage went away.

What might have helped though is that before I switched, I used this stuff to clean out the engine. It worked very well IMO, and as advertised.

I've been having my oil analyzed the last two years or so, to see how long I can run it. The people I use are here; they will send you free testing kits and it's $30 to have them test it. I've sold the 2000, but I now have a 2004 GC 4.0 with 55000 miles, and I'm using synthetic and going 10000 miles between changes.

Hope all that helps, apologize for getting started about oil....

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sreilly77

Hey thanks for all the information, guys. Fredjacksonsan: I checked out the site you had posted and backed up the information you gave me. And toddman67: You make a good point about sticking with what is working with me Jeep despite the mileage. I was just concerned about engine wear because it is a great Jeep and I have done a lot of preventative maintenance on it already so it would last.

I also went on some other websites where people discussed switching to synthetic oil and they too had some oil seeping at first. However after a couple thousand miles, the seeping went away. However, most of the cars that were discussed had only a little over 100,000 miles. I am going to assume that switching at almost 200,000 miles might have worse effects since the engine is older and worn more. Thank you for the information. It really was a great help. I'll just stick with what I have for now since everything is running fine. Thanks again.

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Sean

wrenchboss26

i run synthetic in my 4.0. I guarantee your rear main seal will leak if it isn't already. i change my oil every 8k or once a year and i've got 232k. been on synthetic since about 115k.

toddman67

All to often people think that switching will allow them extra mileage between changes, but fail to recognize that the filter still gets plugged with normal wear and can actually cause more harm than good.

Another point is the price of this stuff. Synthetic oils have kept pace with conventional oils as far as price, even more so in many cases. It's difficult to digest these increases for the so-called benefits.

I use synthetic oil in one of my vehicles but only because that is what it started with. I do not go the full interval that is recommended and pay the premium price for the oil change. I'm a firm believer in stringent oil change intervals, after all this is the life blood of the engine. Be good to your equipment and it will reward you back.

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fredjacksonsan

You're welcome...as a quick side note and since you'll be doing a lot of highway driving, you can always see about extending the use of your conventional motor oil. Blackstone will give you oil analysis and their (conservative) recommendations for extending your oil change interval. Most filters will handle the extended intervals. Our Jeeps recommend 6000 miles for oil changes anyway under easy conditions, so going another couple thousand won't hurt anything - IF the oil still has all the additives, which is why having it analyzed if you plan to increase your interval is a good idea.

Good luck with it, hope you get 350K out of the motor!

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AF's RULES can be found HERE -- Please read them.