synthetic oil on old engine

CStamm · Sep 23, 2003

question about going the full synthetic route on 92 w, 140,000 miles. I read all of the info. I could find, and I'm looking for a final opinion. I believe synthetics to be worth the extra cost. However, with their engine cleaning properties, I am afraid that I will develop more oil leaks. I have a very small leak coming from either my valve cover or my rear main seal (not sure yet). So, although I'd like to switch to Mobil 1, I'm afraid this will cause more and bigger leaks to start form this higher mileage engine. I understand that the crud that could be sealing up leaks is just a mask for the problem, but would i be better off just sticking to regular oil? Any opinions greatly appreciated.

Eagle · Sep 23, 2003

CStamm said:
question about going the full synthetic route on 92 w, 140,000 miles. I read all of the info. I could find, and I'm looking for a final opinion. I believe synthetics to be worth the extra cost. However, with their engine cleaning properties, I am afraid that I will develop more oil leaks. I have a very small leak coming from either my valve cover or my rear main seal (not sure yet). So, although I'd like to switch to Mobil 1, I'm afraid this will cause more and bigger leaks to start form this higher mileage engine. I understand that the crud that could be sealing up leaks is just a mask for the problem, but would i be better off just sticking to regular oil? Any opinions greatly appreciated.

Sooner or later it's going to leak anyway. I replaced my rear main seal at about 160,000 miles ('88 XJ 4.0L), and at 175,000 I switched to synthetic oil. I wish I had changed sooner.

Judd W. VA · Sep 23, 2003

The only way to find out is to try it. Does not actually make much difference whether on a new or old engine. Some new or newer engines do not even tolerate synth engine oils. Could have poor oil control rings or a bad seal or two. Is not a matter of the cleaning ability of the synthetic oil, but that it has a higher film strength allowing it to flow through smaller gaps.

My '98 4.0 with now 85k miles uses no Mobile 1 oil in it's 10k mile oil service intervals!! I find that totally comforting as i hope to accumulate a mass of miles on that thing before wanting to deal with anything major engine related.

Good Luck.

97XJ · Sep 23, 2003

Give this a try first, http://www.auto-rx.com/ some pretty amazing stuff.

Mikel · Sep 24, 2003

I started using Mobil 1 in my 95 4.0 with 135K miles 10K miles ago, and other than a slow leaking rear main seal that was already leaking, everything is good.

Eagle · Sep 24, 2003

I recently refurbished an '88 for a friend and agreed to deliver it to her ... from Connecticut to Montana. Mileage was 164,xxx when I left, and the only oil leak was a tiny drip from the front cover.

Halfway across PA on I-80, I realized that the liftgate was coated with oil droplets. Sure enough, the rear main seal had packed it in. Since I had no tools and no place to work, I bought a case of Wal-Mart 20W50 and soldiered on -- used 7 quarts of oil to go 2500 miles. The same thing happened to Mike from NJ in his '94 when he set out for Moab last year.

We took it to my friend's mechanic when I got to Montana. He replaced the seal -- said the old one was as hard as a rock. So for any XJ of about the same vintage, I'd say just bite the bullet and have the seal replaced, because it's going to need it soon anyway, and then switch to synthetic.

Heinz · Sep 24, 2003

Synth. oil?

I tried syntetic oil on mine(143K, 92 4.0), regu;arly chgd. by former owners, no diff., I think synthetic is good in diffs., as they are a closed system unlike an engine. BUT, synthetics in motor while helping it cool, longer chg. intervals will NOT get out blowby pollutants that can damage your engine. I swapped back(because of cost too) to 10/40 Castrol and chg. it after every 3-5 K. I feel better knowing I'm flushing engine of contaminates and i only lose a qt. maybe every 3-4K. Heinz

Kevin · Sep 24, 2003

What does a rear seal replacement cost?

And since we are discussing synthetics, etc. what about things like gas treatment or high mileage oil? Are they worth anything?

CStamm · Sep 24, 2003

Re: Synth. oil?

Heinz said:
I tried syntetic oil on mine(143K, 92 4.0), regu;arly chgd. by former owners, no diff., I think synthetic is good in diffs., as they are a closed system unlike an engine. BUT, synthetics in motor while helping it cool, longer chg. intervals will NOT get out blowby pollutants that can damage your engine. I swapped back(because of cost too) to 10/40 Castrol and chg. it after every 3-5 K. I feel better knowing I'm flushing engine of contaminates and i only lose a qt. maybe every 3-4K. Heinz

So, your telling me that synthetics don't remove contaminants? I thought that they did that much much better than conventional oils. Am I wrong?

DARKFLY · Sep 24, 2003

in my old toy i used to run mobal 1 & pro long. expensive but worth every penny. it ran so much better than any toy i had ever drove even brand new ones. it would do like 20 foot burn outs on 31 12.50's with out even trying.

ChiXJeff · Sep 24, 2003

Kevin said:
What does a rear seal replacement cost?

The seal itself is cheap. It's only a few bucks.. Labor, OTOH, to replace it, well....... It's a couple of hours of work as you have to drop the oil pan, and at least loosen up all of the crank main bearings.

I did mine in May, but then engine was mounted on a stand. Made it just a little easier.

Sarge · Sep 24, 2003

Re: Synth. oil?

Heinz said:
BUT, synthetics in motor while helping it cool, longer chg. intervals will NOT get out blowby pollutants that can damage your engine. Heinz

Who told you that? Synth does too remove the nasties. Shows it the same as regular oil....by turning dark.

Sarge

AZ Jeff · Sep 24, 2003

I think he was meaning to imply that, since sythetics typically have longer change intervals, the amount of bad chemical residues that accumulate in an older engine between changes would be greater when using synthetics.

I have a solution to that: change the synthetic more often than the manufacturers recommendations.

I run my XJ and my wife's Plymouth mini-van on Mobil One. The van has 139K on the original engine, and was switched to synthetic at about 125K. It does not use much oil (1/2 quart in 3000), but I change the oil at 4000 regardless, just ot be sure I don't have a build up of contaminants in the oil.

The XJ only has 82K on the clock and I change that one every 5000 miles. (It has lived on Mobil ONE since new.)

Hawaiian Style · Sep 24, 2003

Call me crazy but I change the Castol Snytec in my Jeeps at 3000 anyway. I've never left a filter on for more than 3k either. Probably overkill I know but it sure doesn't hurt

jeepster1985 · Sep 29, 2003

I use Mobil 1 full syn every time i change my oil...no problems....sware by it

redrockphil · Sep 29, 2003

I run the 4x4 syn/conventional mix in my 96 with 82K. Been running it since 65K. Change it every 4K. Its a lot cheaper than the full syn, and has some of the benefits from both conventional and synthetic. However, I will be going to full synthetic soon. I just dont believe the mix can be as effective as the full syn.
My motto: If you do it, do it right (unless you cant afford to right away, then do what you can)

XJ88Jeeper · Sep 29, 2003

Geez People Your making me feel like my 88 is an old timer. Just Hit 250,000 Miles And started using A Synthetic Racing Oil With No New Leaks. And The Old Ones haven't gotten Worse.

JeepSpeed · Sep 29, 2003

Mobil 1 full-syn high-performance and a new filter every 3 thousand. For me, I give nothin but the best to the love of my life. Much of the benefits of synthetics have yet to be discussed. Due to the reduced friction, they help cover engine parts better, absorb heat better, and my favorite, actually add a couple ponies. It's a matter of the vehicle, if u really care, I think syn would be better. For the a to b daily driver, there's nothing wrong with the dino oil.

XJ88Jeeper · Sep 30, 2003

Hehe We Buy Only The Best for The Love Of Our Lives, But What About Our Wives and Girlfriends?? HAHAHA

RichP · Sep 30, 2003

syn/organic mixes

Don't waste your money on the mix or blends. If you want to save a few bucks but still get some of the bennies do your own mix of 50/50.
I tried to find out what the blend was from a couple of the manufacturers, was told that the ratio was 'proprietary' which to me says it could be as little as 1/99 and judging by the prices is nowhere near 50/50.
Check out sales, Walmart has the 5 quart mobil-1 containers on sale for ~$18 every so often so I stock up usually with 6 containers and a 6 pack. I also noticed that a case of single bottles of Mobil-1 was cheaper than a 6 pack in a box. Might have been a pricing error but no way am I paying an extra $4 for a carboard box.

synthetic oil on old engine

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