So which type of fluid would be best in the diffs and trans of my semi truck? I hear from some people on a big rig forum that synthetic is a waste in the trans and diffs.
Synthetic or conventional for differential and transmission on semi truck
- Thread starter Redland1
- Start date
What is the reason given that they think synthetic lubricants are a waste in the trans and diffs?
Most OEMs spec 75w90 for differentials and 50wt synthetic in the transmission. It will depend on what transmission you have, the 50wt is mainly for manuals. I like synthetics a lot, I have one truck that is running 75w90 in the differential but any that I service now get 75-140 but I still use 50wt in the transmissions. Extended drain intervals is the main reason along with a slight increase in fuel economy. I believe Eaton rear axles can run factory fill to 750,000 miles on 75w90 if I remember the stickers correctly.
If it's going in your money maker, why wouldn't you use synthetic? Better performance over a longer drain interval for marginally more money. Less downtime for you means more money back in your pocket because you can be on the road more.
Look at motor oils for passenger cars, we used to run conventionals for 3,000 miles. Now, we have synthetics that are manufacturer backed for up to 20,000 in vehicles that support them. Over six times the life span for twice the price.
Value your time.
Look at motor oils for passenger cars, we used to run conventionals for 3,000 miles. Now, we have synthetics that are manufacturer backed for up to 20,000 in vehicles that support them. Over six times the life span for twice the price.
Value your time.
Most trucking companies are in the business of making money and total cost of ownership is of huge concern. Synthetic transmission and gear lubricants offer a much longer drain interval and do cost more, but maintenance downtime for a truck is very expensive as is the act of doing the maintenance. Extending drain intervals, per OEM recommendations, reduces TCO and puts more profit in your pocket.
This is the reason-
"Additive Separation" qualities in an oil usually dictates drain intervals in gear-boxes. - I have not seen any synthetic vs. standard oils have superior "separation" claims with data to back any of them up.
NEXT: you should be changing your oil every 2 years or 250k miles, whichever comes first... despite what the manufacturer tells ya. This is to stave off "Separation" (and sheering) ... Unlike your engine, the main reason gear-box oils stop working well to protect the components.
so -- there is no advantages to synthetic in a gearbox that I can see based on differences in oil qualities alone. - 'Environmental Factors' is usually the only scale for determining synthetic oils vs. conventional, especially in a gearbox. ... but the oil makers would brain-wash you otherwise. How else are they gong to sell you their super-duper-oils if you can't reasonably justify the 2x or more expense differences?. They sell you the stuff on opinion and brainwashing fear alone.. that is how they get you to buy it.
Don’t know,just got the truck.
It’s a 13 speed Eaton fuller.
MolaKule
Staff member
Some of your information is incorrect.
Let's assume a truck sits for a couple of years (sounds like your's are daily haulers). Let's further assume some agglomeration occurs which settles out some additives. Heating and turbulence in gear boxes readily remixes all the chemistry back into solution, so no fear there.
The correct term is "shearing" and may be caused by shearing of the VII molecules due to compressive and sliding forces at the gear teeth and bearings. UOA's can tell you how much viscosity loss or reduction has been encountered at various mileages compared to a VOA, a practice in which all trucking company's use to determine oil condition (oil condition monitoring). Trending and documentation will tell you how the oil is holding up.
As to your last paragraph, and as taschnewitz said, "Look at motor oils for passenger cars, we used to run conventional's for 3,000 miles. Now, we have synthetics [in which the] manufacturers back for up to 20,000 in vehicles that support them. Over six times the life span for twice the price."
There is no conspiracy here, no fear, no brainwashing.
Forgot to say that it was the response I received on the other forum when I asked about synthetic.
I retired from a company that had an old school shop foreman who used only bulk Rotella T4 in our truck engines but would only use synthetic gear oil in the transmissions and diffs. He would do an engine in frame PM rebuild at 1 million miles but I don’t ever remember seeing a truck in the shop having a diff or transmission rebuild being done.