To go synthetic, or not?

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Jan 28, 2005
Baltimore, Maryland U.S.A.
I have a 1987 Jeep Cherokee that has 220,000 miles on it. I use fully synthetic oil in the engine, but the rest of the vehicle uses conventional fluids. I've been told that the Jeep is too old to switch over all the conventional fluids, to synthetic; switching could cause more harm than good. Other opinions say that you can switch at any time. I'd like to keep this vehicle on the road as long as possible. I am mostly interested in possibly switching the ATF, differential fluids (front & back), and the transfer case. So, does anyone have any opinions? Thanks in advance!
For the diffs and t-case, go right ahead. No problems there. For the tranny, what is the fluid change history for it? If it has had regular changes and filter changes, it should not be a problem. But if it has had few, infrequest, or no changes, stay with what is in there.
There's no problem changing over a high mileage auto transmission to a synthetic fluid, provided you are careful w/ regards to cleanliness. I'd drop the oil pan and clean out any residue, then change the filter or clean the screen. Install a new pan gasket, reinstall the pan and refill the transmission. Repeat this process after 3000-5000 miles.... Two partial changes of fluid should remove about 75% of the old fluid and you'll get most of the performance of doing a 100% change out. The problem folks run into with high mileage auto transmissions is when they use one of these flushing machines without servicing the filter and/or removing the oil pan. This loosens up a bunch of organic clutch pack materials and wear metal particles inside the transmission and can quickly clog the filter or screen. Once the flow of fluid is impeded by a partially clogged filter, the clutch packs start to run hot, get glazed and slip. This is often blamed on the synthetic fluid being too slippery, but in fact the fluid has nothing to do with this failure mechanism.... Tooslick
I was always curious about switching over the rest of the Jeep, to full synthetic, but I was afraid to do so because things are running pretty well with the conventional stuff; but I know that synthetics usually give a higher level of protection. I was most concerned with the transmission, and I have heard the horror stories that Too Slick mentions. I had heard that synthetic ATF, in an older transmission, would cause massive slippage and other goofy problems. I was even told that fresh conventional ATF, could cause slippage; some people have told me at 220,000 miles, I should never change the ATF, period! I was told never to do a "power transmission machine flush" because it would also cause problems by stirring up "gunk" in the transmission. I was told to just drain the pan and replace the same amount of fluid with fresh; I think it is about 3 quarts. This is what I've done recently. --------------------------------------------- With the mileage on the Jeep, would it be better to switch to "synthetic-blend" fluids, or maybe just "high-mileage" fluids, to prevent any problems that may crop up with the switch over to "full synthetic" fluids? If "YES", what brands of these "syn-blends" and "high-mileage" fluids would be best, and fairly easy to obtain? If anyone has any other information, join in. [Smile]
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