If the seal is already leaking , it's going to leak like a seive with light grade synthetic .

Try runing a couple of treatments of Auto Rx first ( www.auto-rx.com ), it may just take care of that seal leak, I've fixed countless leaks with the stuff.

-----------Robert
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '92 Ford F350 diesel dually

I'd stick with dino till the rear main is done-- if it leaks now it will leak after the change, and possibly quite a bit more. My 940T with 200+K mi
seems to use a bit of oil, particularly when it is in boost a lot. Mobil 1 is about $8 Canadian a quart here these days, so that adds up. The rear main drips a bit on mine too, which has kept me from synthetic.

Some friends have noted that transmission shops are often cheaper for rear main repairs than general automotive repair facilities. They do it every day and don't seem to see it as quite such a big deal. These cars are a cakewalk for them-- they are used to doing front wheel drive cars with no room to work. Call around a bit-- $800 is a stiff price for a rear main seal.

I swapped to synthetic on my '92 245 4 years ago now-- not a drip of leakage, and it looks really clean when I peek in the valve cover now. A massive difference compared to my 945T which has been on a steady diet of dino. I didn't do anything before changing, but I did swap filters after about 1000 mi. This car uses less than half a quart of oil between changes, which are twice a year. Not too bad for a car with 145K mi.

Good luck!

I switched straight (cold turkey) to synthetic in my 1992 240 with 130,000 miles two years ago. No problem at all, no leaks. However I went back to dino only because I don't think this engine requires synthetic since it receives 5,000 mile oil changes. I suspect very few of these cars die due to internal engine problems where synthetic would have made a difference. However I do run syn in the 850 turbo and the high reving rice burner.
--
1993 240 Classic; 1992 240; 1997 850 GLT; Mitsubishi 4 cyl.

I have heard a lot about a product Auto RX (www.auto-rx.com) on this site as well and on bobistheoilguy.com . It is supposed to clean all the gunk and it stops the leaks by swelling the seals etc ..

My car is 1990 240 wagon at 209 K miles . I switched straight to mobil-1 four oil changes ago (3x3000). I did put 1/3 sea foam for 400 miles before doing that .Also I changed filter after 1500 miles in the initial change. So far all this has started a very tiny leak which I see at the bottom of bell housing ( I do not know which seal is leaking) . If I clean it the oil makes a drop after 4-5 days . It did not leak at all before that so may be the oil is the culprit. As far as running is concerned I do not see any change . I have used quaker state for the 4th oil change. I do not notice any change in oil consumption which was negligible before change. I do not plan to change OCI as most of the trips I take are small . I am also shifting to cheaper synthetics e.g Quaker State . Shell rotella and supertech ( Walmart brand) etc as others have noticed that they are also good oils .
Regards
Gopesh

the rear main job isn't that bad. If you have done a clutch before all you have left is dropping the flywheel. No biggie. and you are already in there so do a clutch job.

But to answer your question. Synthetic will make everything leak unless the gaskets are good. Synthetic is better for a turbo because of its good heat characteristics. With that said, if you don't take your car to the drag strip, or auto-cross it regularly, don't worry about it.

But if you really want to run M1 then don't do a straight switch. Much like changing food for a dog. Don't do it all at once; slowly add to each meal (oil change) until he is used to it. (5 or 6 meals er oil changes)

Hope that helps!

Andrew

I did a sudden dino to syn in my Audi a few years ago and clogged lifters, blew out the gaskets in the oil pans, made the rear main leak... so been there done that, got the merit badge! (it wasn't a fun one!)