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Differential Oil
What is the concensus on oil for the differential, conventional or synthetic?
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11 Replies
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My 89 had the old type and I changed it to syn. I could hear the differance. Most said it was going to be better! My opinion run what it came with. I changed back and noise went away. Tags and front axle I ran syn with no problem. Just my 1 cent on that one. The 89 used 90Wt. Bob
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It looks like synthetic gear oil takes up more shelf spave than the conventional stuff. That may mean most prefer synthetic. Personally, as long as the change interval is and the fact that the regular stuff has so many proven miles, I say stay with conventional. If I drove the coach more I’d switch to synthetic in the engine. At 15K miles a year or less it doesn’t make since to me to change the engine oil either.
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Syn X 90wt If your bus sits for 9 months will syn still be coating the gear surface like 90 wt?
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For the average motorhome owner and the typical annual miles it probably doesn’t matter much which is used. I doubt if we could ever get enough data to point to one or the other as being significantly better.
But I think synthetic would be an excellent choice if someone tows a heavy trailer. Synthetic oil is going to run at a lower temperature and is likely to make a measurable difference in the differential temperature.
The oil change interval of 100,000 miles makes the difference in cost between conventional and synthetic almost meaningless so just on that basis alone I use synthetic 85/140.
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Many moons ago (when I was still working) the company made a change to synthetic gear oil in the manual transmissions and differentials in our fleet. We starting having a lot of seal leaks. I’m just saying…………
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I’ve changed both my 1989 and my 1999 to synthetics; I fall into the exreme use category. I fully agree with Jon’s comments and have experienced no ill effects.
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If they sit a around with syn you will have more seal leaks the other seams to have less affect on seals don’t know why the heat issue is something to think about 70,000 miles a year for 25 years pulling a trailer just my thoughts
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Thinking specifically of how hub seals on all axles are designed and how they work I would be very surprised if synthetic oils of the same viscosity as conventional oils would have more or less tendency to leak.
Hub seals as designed are not going to be affected by lack of use since they are not compressed by sitting in one position or another for long periods. While I don’t think most of us actually need synthetic oils in our hubs or differentials, those that do benefit such as those towing heavy loads should not be afraid to use synthetics because of hub seal leaks.
It is hard to get good data because those addressing the issue of the effects of synthetic oils on seals have a vested interest in promoting synthetic oils, but I cannot imagine any reason why one oil would leak while another would not.
http://www.performanceplusoil.com/myths_of_motor_oil
http://www.motor-oil-engineers.com/FAQregardingsyntheticlubricants.htm
http://www.synmaxperformancelubricants.com/PDFs/SynMax_Tech_MotorOil_Seal_Performance.pdf
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It is my UNDERSTANDING that many gaskets/seals made long ago were not compatible with synthetic lubricant. In fact, Mercedes specifically recommended against the use of synthetics in my 1957 300SL rdst but had no problems with vehicles built in the 70’s. The other issue is synthetics tend to have better detergent action and, if used in a poorly maintained unit, may clean it up and indirectly cause seal leaks.
I’ve had wheel seal problems on synthetic and dino oil. I’ve switched my 1989 and 1999’s diffs and transmissions and the 1999 series 60 and have experienced no leaks I can attribute to the oil.
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It’s been my experience that vehicles that are well maintained there still seems to be a issue with synthetic oils in wheel seals. Mostly the biggest leakage that I have had to repair has been on the less used vehicles, caused by what I believe to be dry seals. Just a side note, after I fixed the leak by changing the seal it leaked again when syn oil was used and did not leak when new seals and conventional oil were installed. I do use syn oil in the drive axels in my Peterbilt and in the Prevost and I havn’t had any leaks so far. The trailers seem to have some issues with leakage when syn is used. I have yet to discover the reason for this.
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The old stinky stuff we paint plow mold boards with never rust. But used some old syn and it flash rusted on us. Just a off beat use of old rear end lube. Bob
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