synthetic vs petroleum based oil?

I have three vehicles, a 1982 300 TDT Mercedes, a 1989 Toyota 4Runner w V6 & 4WD, and a 1985 Toyota Corolla GTS 1600 cc dual OHC.
I bought the Corolla new and have changed the oil every 2000 miles. It
has 260,000 miles on it. I bought the 300 TDT with 144,000 miles on it in 1993. I changed the oil every 2000 miles. It now has 394,000 miles on it. I bought my 4Runner on eBay 3 years ago with 252,000 miles on it. It had synthetic oil in the gearboxes, and after some research I decided to put syntheitics in all my vehicles in both the gearboxes and engines. My 4Runner has 274,00 on it now.
When I did this in 2003 my Corolla did not ever need oil added between changes. Neither did the 4Runner, and the Mercedes, despite very high mileage, usually did not need oil added between changes, but sometimes was near the add mark at 2000 miles.
Now the Corolla needs oil after 1200 miles or so, the 4Runner needs oil after 1400 and the 300TDT has really gone to hell. It's lost compression and blows out a quart of oil in about 500 miles because of increased blow by and will not start in just cool weather, forget about starting in cold weather.
The gearboxes have fared better. I like the way the automatic in my 300TDT shifts with synthetic, and the rear end gearbox works fine with synthetic gear lube. The same is true with all gearboxes on my 4Runner. The rear end, with limited slip, in my Corolla is fine, but last winter I was at the Grand Canyon and it was very cold. Overnight the synthetic lube in the tranny leaked out through the seals when the metal got cold and contracted and the synthetic stayed thin. I didn't notice, and by the time I got to Page, UT, about 100 miles away, I had damaged a bearing in the tranny. I would be very careful about putting synthetic in a gearbox with older seals.
I will never use synthetic in an older engine again. I don't know what it did to the engine in my 300 TDT, but it sure coincided with a rapid deterioration of the motor that had been stable for a long time.
I have switched back to Pennzoil in the 4Runner and am going to do the same with my Corolla as soon as I get the bearing replaced in the transmission, which I pan to do some time in the next few weeks. I used 15-40 Chevron in the 300 TDT for years and have switched back to that for now until I do a complete overhaul later this winter.
What do people on the list recommend for engine oil in my 300 TDT after get the overhaul finished?
Paul Fretheim
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I would use 15w40 Diesel spec mineral oil. That engine was not designed for synthetic oils. And consider how many miles you have left in the chassis.
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I still would have used synthetic oil after the rebuild. Diesel specified synthetic oil only... not just Mobil 1... majority of Mobil 1 oils are not for diesel. They don't have the additive to suspend that carbon deposits.
Shell Rotella Synthetic is designed for diesel engine... available at Wal Mart in quart and gallon size at $3.99 per quart on the gallon container.
The reason why your engine last so long is because of your 2000 miles oil changes... because when regular oil get to 3000 miles, it really starts to decline in performance.
I would put back regular oil in all your vehicles for now... especially the diesel and see if it resolves itself.
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heav wrote:

I think your experience answers your question. If I were you I'd go back to a good Pennsylvania grade petroleum based motor oil. Be sure that the oil has the proper additive package for diesel service. What I said in the previous article in this group "Oil Change every 3,000 mi? 1992 300E 112,000 mi", explains my logic. it has been my experience that synthetic oils cause considerably more engine wear than petroleum based oils. In my experience Pennsylvania (paraffin based) oils to offer the longest engine life, particularly in diesel service.
EJ in NJ
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Chassis is good. I have replaced any parts, including springs, when ever they got worn out or failed. The front end has been completely rebuilt in the past 30,000 miles. I had to find a custom rebuilder to get a new driveline as Mercedes does not offer parts for the driveline.
I am going to rebuild the drivers side front seat also with new springs and horsehair pad from Mercedes.
I have replaced all the climate control components in the past few years. Everything works on the car. It is a California car and the clear coat finish is still shiny and looks almost like new, with only a few nicks and scratches. No dents. I have replaced the windshield 3 times, and it is due for another new windshield.
Paul
heav wrote:

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heav wrote:

Interesting story. About 30 years ago, I had a Fiat 124 Spyder, which I had purchased new. Initially I used regular oil in it. But Mobil 1 had just come out, which I think was the first synthetic that was widely marketed for passenger car use. I tried it and had a similar experience. The car, which only had maybe 15K miles on it, went from not needing any oil between changes, to consuming more than a quart. I wrote Mobil about it, and they refunded my money.
I went back to std oil, changed it regularly, then at some point, and not a lot of miles, (maybe 50K?), I had a head gasket blow. When they went to replace it, they told be the valve guides were all shot, and questioned if I changed the oil regularly, implying this was unusual. Of course, this car was such a piece of junk, that nothing really would surprise me.
But anyway, it is similar to your experience. I would not switch and use synthetic in a car that has been using conventional. Most important is frequent changing of the oil. I do use sythetic in my Porsche, which is what is recommended. And here's another classic. Porsche has two different lists of oil weights depending on the temp. Since I live in NJ, where the winters are pretty mild and the summer temps not extreme, you would think you could use one grade all year. You can, but the only grade on both lists is 10-40, and the only synthetic I've found that offers that is Castrol. Yet, Porsche recommends Moibl 1.
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You probably won't find it at discount stores, but Mobile One is availabe in 0/40, which is even wider in application that 10/40.
Paul
snipped-for-privacy@optonline.net wrote:

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Again... Mobil 1 oils are not for diesel unless it is specifically said so.
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