Synthetic Fluids

I need to take my XJ in for new fluids (Tranny, Brakes, Engine, Coolant). What's you experience with using synthetic's? Someone told me that being an older engine, the synthetic oil would more than likely leak.

I've had my XJ for a week now and the condition of the fluids does not look healthy, I was told that at least the engine oil was changed before the purchase. but I doubt it.

All sugestions pro/con will be greatly appreaciated.

Should I just stick to regular fluids?

When synthetic oils were first brought to market, they were so slippery (due to extremely small molecular structure) that they did weep around seals and gaskets. That has supposedly been corrected with current formulations.

I changed over my '88 XJ to full synthetic at 175,000 miles. I had previously changed the rear main seal, but never touched the valve cover. I have no leaks. Ditto my '88 MJ, which I changed over to synth at 100,000. I was originally using Mobil-1 but now I use Castrol because it's available in a 5W50 formulation.

I would go for it.

There is a bit of misunderstanding about what Synthetic oil is. I am not a chemist so take this for what it is, but I think this may help you to make a more informed decision. All oils are made up primarily out of chains of carbon (plus whatever proprietary additives they put in). For a given weight these chains are supposed to be a given length. With natural oil what they do is separate the crude into different components (chain length) and what you get is a bunch of chains that are about the same length. With Synthetic what they do is take the crude and break it down and then build it back up. This produces an oil that in far more accurate in the length of it chain. They are all exactly the right length. When you use these oil’s, synthetic or natural the chain sometimes break, this essentially contaminates the remaining oil with these shorter chain. So all that the synthetic dose for you is start you of exactly where you want, instead of about where you want. There is nothing stronger or inherently better about the molecules themselves. For me a good quality natural oil like Castrol, changed religiously every 3000miles is as good or better then a synthetic changed every 7000.

You might want to search through posts, but for tranny... synth is ussually a bad idea...
if your tranny is AX15... the only one that you can run safely is the dino from dealer which has GL3 spec on it...

if you have aw4, quite a few people report weird performance of the tranny after putting synths in...


Engine... Mobil 1 all the way for me Axles... well, it's a toss up...

Kejtar

For you guys that use the synthetic in your engine how often do you change you oil?

I drive a lot... and it's all in stop and go traffic... Due to those two factors.. I do mine between 3K and 5K (more like 4.5K )

Kejtar

Bronco said:

For you guys that use the synthetic in your engine how often do you change you oil?

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When I ran conventional oil I changed oil and filter every 2500 miles. With synthetic I change oil and filter every 5000 miles. That may sound like a lot, but my brother is a service rep at the local BMW dealership. BMWs come from the factory with synthetic oil, and their recommended change interval is 15,000 miles.

Considering that the factory recommended severe duty interval for Jeeps on conventional oil is 3500 miles, I don't think 5,000 with synthetic is extreme or excessive.

There are two reasons to regularly change oil in an engine:

1. oil contamination--accumulation of byproducts of combustion, which contain acids, etc. that eventually start eating away at the more delicate parts of the engine (the BEARING SHELLS)
2. oil breakdown--as oil is exposed to extreme heat in the engine, it literally begins to chemically alter so it no longer provides the lubricating film properties it had when new.

Synthetics are MUCH, MUCH, better at tolerating heat damage that are mineral based oils. That is their main claim to fame. However, synthetics, for the most part, are no better at dealing with the contamination factor listed above.

With all this said, here are my personal thoughts: if you live in an area where it gets very cold (below freezing), or very hot (above human body temperature) synthetics will do things better than mineral oil, because they hold their viscosity across temperature more evenly.

I live in Phoenix, so with summertime temps on the pavement at 140 degrees F or more, I feel that synthetics prevent oil breakdown more effectively. I change oil and filter every 4500 miles.

If your engine leaks after running synthetic in it then it's time to replace the seals. Synthetics have more detergents in them and so they clean the sludge out of all the crevasses in the engine. That includes the sludge that may be blocking leaks. IF you switch back to dino, the sludge can build up again and stop the hole up again but you're only covering up the problem. Synthetic isn't better just because it lasts longer or because of the higher detergents, but it's also just a better lubricant. I won't run anything else in any engine of mine that matters to me.
I usaully change it about 6-7k; most of my miles are long trips. I just watch it and when it starts to darken I change it.

Synthetic oils......

Synthetic oils have a higher film strength. It is because of this higher film strength it can seep past seals where organic oils do not tend to.

There is no GL-3 synthetic oils available that i have found. Auto Zone has GL-3 to 5 gear lube that is compatible and far more cost effective than the dealer.

Some of the most particular auto makers (as with Porsche, BMW) insist on Mobile 1 oil. They know more about the oil science than do i, and that is a good enough reason for me. Since Castrol is not a true synthetic, i tend to stay away from that one.

A Jeep group here in the Valley do as a regular routine oil testing. They have found on 4.0's in good shape Mobile 1 seems to last around 25k miles!!!!! To me that is very significant. I personally go 10k miles on my Mobile 1 and Mustang GT M1-301 Mobile 1 filter. Even in that time/mileage the oil is not that dark- therefore should not be sludging.

At 33K miles swith the XJ to synthetics except tranny. Read both sides of the debate and decided the AW4 works well on the dino so stay with the dino.

Engine Mobil 1 every 5K with K&N oil filter
Frt diff 75W-90 Valvoline syn
231 Valvoline Syn ATF
Rear Diff Valvoline 75W-140 as recommended for trailer towing.

Now have 50K miles and no leaks. I thought that the Mobil1 would allow me to extend the oil change intervals but the oil is black at 5K even the times I changed just the filter and make up oil at 2.5K.

good luck,
Tom

Re: Synthetic oils......

Judd W. VA said:

Some of the most particular auto makers (as with Porsche, BMW) insist on Mobile 1 oil. They know more about the oil science than do i, and that is a good enough reason for me. Since Castrol is not a true synthetic, i tend to stay away from that one.

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Accordingto my brother, who works in a BMW dealership service departmentand used to manage one, BMW's synthetic oil is Valvoline, packaged for BMW. And Volkswagen's synthetic is Castrol. Castrol is fully synthetic -- claims that it isn't are sour grapes from competitors. This has been debunked enough that it really belongs on an "urban myths" web site. And Castrol has a 5W50 formulation, which is great for older engines with high mileage, because you still get the 5-weight for start-up but you get the 50-weight for hot running. Mobil-1 only has a 15W50, which in my neck of the woods isn't great for winter when the Jeep is parked outside on sub-freezing nights.

BMW Synthetic info: http://www.sts.sae.org/membersonly/techinfo/servicetech/tech-tidbits-03.pdf

Actually neither Mobil 1 nor Castrol are "full-synthetics" in most technical sense of the word. Mobil 1 sued castrol because it was only "synthetic-enhanced" dino rather than starting out fully synthetic. Since they lost that lawsuit Mobil 1 has switched and is now doing the exact same thing ( the "Tri-Synthetic" reformulation).

Here's a good write up I ran across while finding some info about synthetics... it's about half-way down..

http://www.micapeak.com/bike/ST1300/Oils.html

EDIT: I believe the 5w-40 Mobil 1 that BMW recommends is the Delvac (or whatever) version that is still full-synthetic. THat is the only 5w-40 Mobil 1 oil I have seen.

I go natural with very regular oil changes just to recycle the byproducts out.