06 Tundra rear diff, Amsoil SVG 75W-90, 44K miles

[btanchors]

Well, this UOA seems to indicate an increased amount of wear compared to previous samples, even taking into account the longer miles. I am not sure what might be causing it. I do not think this amount of iron is particularly excessive, I am just a bit surprised at the amount compared to previous samples. The amount of material on the magnet was pretty minimal. Comments?

 

[Turk]

Wow, more than double Fe from last time. Just think what all the vehicles have for Fe that don't have it changed!

Thickened up some as well. Doing anything different with this truck? Heavy off-roading?

 

[JerryBob]

What did the magnetic drain plug look like? Any chance the fill and drain plugs look alike, and that you reversed them?

 

[lubricatosaurus]

Originally Posted By: JerryBob
What did the magnetic drain plug look like? Any chance the fill and drain plugs look alike, and that you reversed them?

Or the magnet aged and lost magnetism force. Happens with thermal aging. New magnetic drain plug, or test the old one compared to a new one, force to stick on sheet metal.

 

[ARB1977]

Man I went 60K on the same oil in my diff. The oil looked pretty good.

 

[Trav]

If the diff is quiet I would suspect its probably coming from wheel bearing, these are known for it.

if it is then oil brand wont help its a material hardening failure.

 

[mongo161]

Was the oil "Gray" and cloudy when you changed the fluid?

 

[oliveoil]

It really looks like the extra fe is due to increased so. Some dirt got on the end of the full hose and made it's way inside. I always have to be careful when opening or using the fill-hole plug.

 

[oliveoil]

Increased si. (Spell checker)

 

[MolaKule]

Why not try the SVG or LE 75W110 and get a bit of extra film thickness between the gear teeth and in the bearings.

If this is the same oil fill from the beginning, iron ppm IS accumulative.

 

[aquariuscsm]

Were all your previous UOA's with SVG 75W90?

 

[zeng]

May I know if your factory manual specs 80W-90 / 75W-140 ?

Edit: Is the used oil color goldish amber or dark grayish ?

 

[btanchors]

Wow, lots of interest in this UOA. I will answer the questions asked:

1) Someone mentioned the drain plug. There was NO confusion between fill and drain plugs - the drain plug has a magnet and the fill plug does not. No question the drain plug had the magnet.

Having said that, a funny thing happened. When I removed the drain plug, I set it aside because I wanted to examine it more closely. I was careful not to disturb the accumulation on the magnet. Then, when I went to fill the diff again, I couldn't remember where I put the drain plug. Fortunately, I had a new one in my parts bin, so I installed a new one. Then later, after I was done, I found where I had put the original drain plug, still undisturbed. I set it aside to examine later. I will take pictures of it and post here, but it may take a day or two to get to it.

2) No known changes in operation, or service. My 21 year old son drives this vehicle exclusively now. Although he claims he hasn't done anything unusual, he does drive more aggressively than the previous driver represented in earlier UOAs (my wife). He did not tow anything during the interval, nor did he go off-road with it.

3) The drained oil did not have a grayish hue to it, but it was darker than the drains of the front diff and transfer case. Those other two compartments used the same oil from the same lot, and were in service for the same exact miles.

4) All UOAs posted above used Amsoil SVG 75W-90.

5) The differential is quiet and is not making any noises. Note that this is a mechanical Limited Slip Differential. All the previous UOAs, including the current one, have 4 ounces of Amsoil Slip-Lok additive incorporated. I did note this on the slip enclosed with the sample to Blackstone.

6) The manual specs SAE 90. There is no recommendation for anything heavier. I believe it does recommend SAE 80 for operation below 0 degrees.

7) I did not notice how much silicon increased in this UOA - thanks for pointing it out. I am very careful when filling - I use a plastic pump, using the same one for all three compartments. I usually direct the first one or two "pumps" of fluid into the drain pan to flush out any dirt that may have gotten into the pump while moving between compartments, but I am careful not to let the hose touch anything. Still, obviously more Si got in there somehow. Compared with the previous UOAs, I would think the increased Si is most likely what caused the increased Fe - what do you all think? Iron was certainly much lower in all the previous UOAs, but so was Si.

 

[zeng]

It appears to me the rear differential is subjected to heavier duty in relation to the front differential and transfer case.

It would be nice to see end-of-life used gear oils carry some gold-amber color instead of gray/dark gray.

The 'extra' Fe from UOA comes from rear gearsets , whichmay eventually lead to whining sound being generated with continued use of 75W-90 instead of factory spec'ed SAE90.

I would suggest you 'monitor' potential whining sound.

Just my 2 cent.

 

[btanchors]

zeng - OK, I agree and concur with all your comments above, except use of 75W-90 leading to whining sound being generated. At operating temperature, 75W-90 and SAE 90 are the same weight.

At cold temps, the 75W-90 would be thinner than the SAE 90, but both would be much thicker then they are at operating temperature.

So I do not see how use of 75W-90 would lead to whining.

You did not say anything regarding the much larger amount of silicon in this latest UOA - you don't think this caused the larger amount of iron?

Thanks for your comments.

 

[zeng]

Originally Posted By: btanchors
zeng - OK, I agree and concur with all your comments above, except use of 75W-90 leading to whining sound being generated. At operating temperature, 75W-90 and SAE 90 are the same weight.



You are quite right, but there is a difference , of significance , btanchors.
Let's assume the differential gear oil operating temperature is 60 C.
a)Select a typical Esso Gear Oil ST 90 :KV40 at 198 cSt; KV100 at 17.5 cSt ---- it's operating viscosity is 71.5 cSt.

b)Next select a typical Mobil 1 Syn Gear Lube LS 75W-90 :KV40 at 106 cSt; KV100 at 15.2------it's operating viscosity is 47.8 cSt.

IMO, this 71.5 cSt operating viscosity oil( inspite of being a regular mineral oil), offers better wear protection than a 47.8 cSt oil.



Originally Posted By: btanchors
At cold temps, the 75W-90 would be thinner than the SAE 90, but both would be much thicker then they are at operating temperature.



You are absolutely right, at cold temperature, 75W90 is well suited to say, -25C. However minimum ambient for SAE90 is around 0 C. So if your winter ambient is below 0 C, you may adopt the next option of 75W-140 synthetic.

Originally Posted By: btanchors
So I do not see how use of 75W-90 would lead to whining.



Prolong use of sub-optimal operating viscosity oils, in relation to a thicker oil at operating temperature , would generate higher quantum of gear tooth sliding metal wear , leading to increased gear backlash and increased heat... increased temperature ............ eventually gear whine after say , 10 years or so.

Originally Posted By: btanchors
You did not say anything regarding the much larger amount of silicon in this latest UOA - you don't think this caused the larger amount of iron?Thanks for your comments.



The portions of silicon arising out of dirt/sand contamination would aggravate abrasive wear on gear tooth.It's something that ought to be contained. IME, sub-optimal operating viscosity of 75W-90 in this particular case, is the major culprit.

Correct me if I'm wrong.

 

[btanchors]

zeng -

Thanks again for responding. I do not disagree with your data above, but I am still having difficulty concluding that the 75W-90 is the cause of the increased wear. If it indeed was the cause, why did I not have elevated levels in all the early UOAs? The same brand and weight of oil was used in all the previous UOAs.

At any rate, perhaps it may make sense, as Molacule suggested, to move to a 75W-110 weight for the next change.

I will say - there are very few SAE 90 weight differential gear oils available. In fact, Toyota dealers generally use 75W-90 from what I have seen - there are going to be a lot of worn Toyota diffs if this is wrong.

I do note that the newer Tundras (I did have a 2011 for awhile) specify 75W-85 for their differentials. Even my new Tacoma specifies 75W-85. I presume these diffs were specifically made for this viscosity.

 

[MolaKule]

Quote:
If this is the same oil fill from the beginning, iron ppm IS accumulative.


Do you understand what "accumulative" means?

It appears you added the SVG oil about 14,808 miles?

Is this correct?

 

[btanchors]

Mola -

All UOAs represented on this sheet utilized Amsoil SVG 75W-90. I think the first time I changed it was around 5,000 miles, but I did not perform a UOA then. The oil was changed immediately after every sample on this sheet was taken - so I do not see how the iron could be accumulative, since we're dealing with a different fill of oil in each UOA.

Does this address your question?

 

[MolaKule]

It wasn't clear when you added fresh oil.

So at or after 10.3k, 14.7k, 28.6k, 36.8k, and at 43.9k, you added a fresh charge of SVG 75W90?

My concern was: if this was the same oil charge throughout the chart, the iron wear in ppm will accumulate.

Now, if theses results are with NEW oils during each time interval between the tick marks, you may have an internal problem NOT related to the gear oil formulation.