Mixing Axle Lube

[chazzone]

Is there any advantage or problem with mixing the 3 different viscosities of AMSOIL Sever Gear?

I drive an '89 Ford BroncoII that has been heavily modified for the work and play that I do, including off-road work, hauling, and pulling a trailer and boat.

I put a lot of miles on the truck (more than 300k, so far) and I need good mileage as well as protection for the 8.8 that I just swapped in.

Thanks for your thoughts,

-zz

 

[Eddie]

Ask Amsoil. The usual recomendation is to NOT mix gear oils due to different additive packages.

 

[chazzone]

Amsoil says that although their products are compatible with other oils, they will shorten the life or effectiveness of these other oils.

They do not recommend against mixing their own products.

I have an inquiry in to them, as well, and will post what I get from them

-zz

 

[chazzone]

Here is the response I got from AMSOIL:

Charles;

I see no advantage in mixing different viscosities of AMSOIL Severe Gear Oils. My advice is to use one of them, probably 75W140, for maximum protection in all situations.

Thank you for this opportunity to respond to your question(s). As always, please feel free to contact us again if we can be of further assistance.


Sincerely,

Byron Selbrede
Technical Services


I pretty much felt like I was being blown off by this guy, so I wrote back:



Really...you see no advantage.

Maybe you could help me out then. Would mixing give an "average", or do distinct characteristics of each viscosity remain?

You also didn't say whether there would be any problems mixing.

Since I'm considering paying 3 times what the average product costs, and have to go through the hassle of ordering your product, rather than buying it from a legitimate retailer, you might want to consider a more complete answer.

Thank you,

To which their response was:


Charles,


There is no significant repercussion to mixing multiple viscosities. We
do not recommend it because when you mix for instance a 90 weight with a
140 weight you are not creating a "common product" or an average of the
two you just now have two different weight lubricants in the
differential. The manufacturer's recommended weight is what we recommend
you use in your differentials.

-Brandon Irons
AMSOIL Technical Service Representative


So, there you have it. I'm not sure why having distinct viscosities would be a bad thing, but at least we know that they are compatible.

-zz

 

[widman]

When it comes to viscosity, any company has to be very clear in their recommendations. If the gear manufacturer said 75W-140 (or whatever) and they said, sure, you can mix 75W-140 with 75W-90 (or whatever) they are afraid you will sue them when there is wear.

I tore down some Scania truck transmissions (with the Scania factory rep) that failed at 40,000 miles. Both he and I agreed the failure was viscosity related. Fortunately I had my written recommendations to the owner that agreed with the Scania book: 85W-140. I asked the owner's mechanic what he was using. He said 80W-90 and "if it was good enough for Volvo, it was good enough for Scania" He wanted to standardized their 8 Scanias and 6 Volvos with one oil.

My answers to customers are usually a little more detailed (and to the point) than what you posted, but I try to make clear that if they vary from what the manufacturer says, it is their responsibility.

So neither Scania nor I had to foot the bill for 8 transmission repairs.

 

[gtx510]

Would mixing 75W-90, 75W-110, and 75W-140 just give you 75W-110 anyhow?
vis @ 100C would average out to 20.9cst, vs 20.4 for SVG 75W-110

 

[chazzone]

Originally Posted By: gtx510
Would mixing 75W-90, 75W-110, and 75W-140 just give you 75W-110 anyhow?
vis @ 100C would average out to 20.9cst, vs 20.4 for SVG 75W-110


According to AMSOIL, it would not. It would give you 1/3 of each, just sitting in the differential, each waiting to do its thing.

Would this be a bad thing?

Consider that a differential holds about 3 quarts of lube (I know they're all different, but just for ease of computation). Each sitting there waiting to work, but maintaining its own associated properties until they are stirred up by moving gears. Even though it is assumed (based on AMSOIL's assertion) that the viscosities remain distinct, there has to be some amount of blending that goes on as agitation continues. Also, based on the info from AMSOIL, the different vis are fully compatible, meaning that one additive package does not conflict with another.

Wouldn't it be reasonable to assume that when cold, the quart of 75W90 would get rolling faster to protect the gears early on, then as the temp or pressure increased, the higher viscosities which would have warmed up and gotten moving on their own, would continue to provide protection as the need increases?

Indeed, since the lube would have to be well mixed once the diff reached a point of needing increased protection, couldn't we count on the higher vis to step and do their job?

Now, I know the point of a multi-vis lube is to provide superior protection through a wider temperature range, but if this was really true, then why even make the 75w90 and 75w 110? Why wouldn't you just make 75w140 to cover the whole lot?

Thoughts? Enlightenment?

Thanks,

-zz