Late last fall I was starting a job close to home, just 2 miles away. With winter setting in I thought it might be a good idea to switch over to synthetic. Went with Mobil 5-30 and an M1-102 filter. My T had 107K on it at the time. About a month and half ago I was coming up on the 5K OCI. One morning I came out and found oil on the driveway under the truck. Nice new grey pavers! I wiped everything down and drove it. The leak was fom the rear main seal. I was really freaked out. Finding the time to deal with it myself is not easy lately. Giving it out is painful to think about. The few times, except once, that I had work done I ended up miserable. I really hated the thought that the seal was toast. Anyway, I dumped the Mobil 1, then went with Valvoline High Mileage 10-30. Within a day I was told to get rid of it. Seal swellers are bad, so I was told. Dumped the Valvoline and went with Castrol GTX 10-30. Within 100 miles, no more drip. At that point I started an Auto RX treatment. Now, 800 miles later, it's bone dry!

It's been a lesson learned. I won't plead complete ignorance here. I'd heard warnings before. But, for every one warning, there were ten tales from others that claimed to have added synthetics at 150K with no problems. Maybe it's true. Not for me though. I don't have that kind of luck. <img src="/forums/images/graemlins/shiner.gif" alt="" />

Interesting to hear about the high mileage concoctions. I tried the Castrol variety but think I may have been too hasty to change over from trusty old GTX. Your experience is precisely why I did not go to synthetic once I topped 100k. Thanks for relaying that.

It could've been that it was cold (rubber seals contract a bit) and the thinner synthetic could've cause the leakage. With the warmer weather, the seal could've tightened up a bit. Also, you might want to give yer PCV valve and associated hoses a check over... <img src="/forums/images/graemlins/wink.gif" alt="" />

I checked out the PCV system right off the bat. All clear AFAIK. There's no oily mess near the trottle body either. I don't think blow by is an issue with this particular motor.

BTW, my friend's regular mechanic refused to put synthetic in the T he picked up last year. It had 113K miles on it at the time. Naturally, my friend relayed this to me only after I told him what had happened with mine <img src="/forums/images/graemlins/drunk.gif" alt="" />. I might've tried it anyway.

Hmmm...
I switched to Mobil 1 5W30 around 170K... I'm at 196K now... no leakage that wasn't there already (I have some seeping around my valve covers). So, like you said, for all the bad stories there are good ones as well. I've been really happy with the Mobil 1.

Joel

Yup I am seeping around the valve covers too but my seals are probably hard as a rock with their age. I figure they're wear items and they will be replaced when I get around to adjusting my valves. It's a small leak and I would not have noticed it if it wasn't for a nice bead blast job on the transmission while it was apart.

I have been buying only Mobil-1 for years and Syntec too since it's been available - it's cheaper. I have never had a sludge problem form and one August when I was a kid I even drove halfway down the east coast with a thermostat that wouldn't open, ridiculously overheating the Datsun. My cheapskate father likes Pennzoil, broke his fan belt and drove ten miles home and found the engine seized in the morning.

Further I tend to notice about a 10% MPG increase immediately after changing oil. I have been reluctant to take this at face value but some friends have corroborated this to varying degrees.

That's generally been my experiences with synthetics as well. Wet spots become leaks, and leaks become flows. As good as regular oils are these days, I just don't seen the need for synthetics in my vehicles.

I've had fairly decent luck with the high mileage oils on some older high mileage engines. Didn't eliminate the leaks, but it definately slowed them down.

Adam, what are you running in your gears? Mine were pretty stiff going out the driveway this summer; Runner started life down in Anchor Town. 130K on it right now; was thinking about a trip to the Mobil 1 shop this summer.

There I do run syn. I've been using 75/90 Mobil1 for a few years and when I get done installing this traction bar am going to refill with the same weight Royal Purple. PITA finding enough of that stuff around town to do two diffs, though, so it'll have to be some good stuff for me to go to the hassle of finding it again. I've never noticed any appreciable drag with Mobil1. With conventional Valvoline in the cruiser on the other hand...egads.