Comparing Synthetic Oil to Petroleum Based Oil.

To compare synthetic oil to petroleum based oils might be be a waste of time but it's important to find out a few details to insure us that the extra expense is worth it. Regarding our automatic transmissions that was the first consideration in our fleet...the cost was 4X higher than regular Dexron III and IV.

We had experienced some clutches wearing out on severe runs around 2005 and can't say either way if it was the the transmission design back then or the Dexron petroleum based oil causing this problem.

We switched over a several years ago and all our transmissions are now running synthetic oil. I'm happy to report that since then we have not had any mechanical failures and decided to change oil every 3 years for all units ....keeping it simple within our PM program.

We are running 74 buses with Allison 3000 and 2000 models so switching over was pricey. The instructions we got was to drain the Dexron and fill / run the transmissions for 30,000 KM then drain and refill again with synthetic.Newer buses we ordered with Synthetic oil from the factory.

Lubrication
Synthetic oil changes viscosity very little during various temperature ranges while petroleum ATF is more unstable and viscosity is effected more during cold to hot running temperatures.

Wear Protection
Assuming both oils have the same anit-wear additives the higher thermal stability of synthetic oil increases it's anti-wear performance compared to regular ATF.

Heat Dissipation
Heat transfer of both oils is similar but at high temperatures petroleum ATF breaks down and flashes to vapor or vapor/liquid combination causing heat transfer to greatly diminish. I've seen ATF when it's cooked and produces a gross popcorn smell!


Hydraulics
Heat dissipation as noted above is an important factor when it comes to shifting. If an oil cannot handle the heat and accumulates vapor (which compresses easily) then trans shifting efficiency will be greatly reduced.

Anti-Foaming 
Anti-foaming additives also are an important point to add to this list ....since foam contains air shifting will be hindered. From what I found out both oils have similar quality levels of anti foaming agents.

In Conclusion
These are important factors to consider and in my view... go with synthetic oil.  The reduced maintenance offsets the cost of the oil. We change the oil and filters every 3 years compared to every 40,000 KM before synthetic.

The zero failure rate within our fleet is phenomenal and looking at the cost of a Reman Allison transmission you could buy truckloads of synthetic oil.

Please share this post and leave your comments below if you have any experiences yourself or just want to add to my information :)