Sorry, but your belief's about how oil works, your terminology, and your understanding of relationships between basestocks and additives are far from accurate. I would suggest your read the oil faq that is on the 80's page and spend some time on bobistheoilguy.com to get a fundemental understanding.
Can I use 75W-90 diff oil?
- Thread starter DoctorJay
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Sorry, but your belief's about how oil works, your terminology, and your understanding of relationships between basestocks and additives are far from accurate. I would suggest your read the oil faq that is on the 80's page and spend some time on bobistheoilguy.com to get a fundemental understanding.
The protection of a gear oil is not primarily in the oil's viscosity but in the additives. If the oil meets GL-4/5 I doubt the visocity makes any appreciatable difference at all in wear protection.
The multi-weight tests are so far out of date that many of the oils could now meet the standards to qualify for several designations and just choose which one to place on the bottle for marketing purposes. I am pretty sure any of the 75w-90 weights could be properly labled as a straight 90 weight oil if they chose.
I've been using Amsoil 80w-90 in the diffs and their 75w-90 in the T-case but will probably just stick with 75W-90 all around on the next change.
The multi-weight tests are so far out of date that many of the oils could now meet the standards to qualify for several designations and just choose which one to place on the bottle for marketing purposes. I am pretty sure any of the 75w-90 weights could be properly labled as a straight 90 weight oil if they chose.
I've been using Amsoil 80w-90 in the diffs and their 75w-90 in the T-case but will probably just stick with 75W-90 all around on the next change.
Last edited:
Cary, I wonder if you can help me clarify something I recently heard. A mechanic, very good one, told me that sythetics were excellent for engines and some manual transmissions and transfer cases, but not so good for front or rear differentials that have high shear forces at work. His reasoning was this: Dino oils tend to be long chains of molecules. Synthetics tend to be small clusters of molecules. When the gears come together in a differential, the chains take longer to get out of the way than the clusters, thereby creating some additional cushioning. (Of course, when the chains break down, that effect is lost.) This cushioning leads to less friction and heat.
That seems to make sense to me, is it true? The mechanic gave up about a $80 sale of sythetic gear oil to tell me this, so the credibility is certainly there. He has several trucks. He said the only ones in which he has had rearend trouble were the ones in which he used sythetic.
I run Mobil 1 in the engine, but I am dyno everywhere else. Its cheap enough to change regularily.
That seems to make sense to me, is it true? The mechanic gave up about a $80 sale of sythetic gear oil to tell me this, so the credibility is certainly there. He has several trucks. He said the only ones in which he has had rearend trouble were the ones in which he used sythetic.
I run Mobil 1 in the engine, but I am dyno everywhere else. Its cheap enough to change regularily.
I give up, it's like trying to teach a pig to sing. There is no such thing as multiweight tests, and the weights of oils that denote thickness have not changed in years.
Sometimes it is just better to shut up if you don't know what you are saying, rather than jump in and further confuse the issue by uttering gibberish. Trying to even respond and correct the misinformation you have put out is impossible because vitually all of the information is wrong.
Tell him to stick to wrenching and leave lube engineering to chemists.
The most important things when looking for oil in order are:
1) Is it the right product for the application. i.e., SM rated oil for the engine, The proper ATF for the Transmission, GL-5 for the diffs. If you don't get this right, nothing else matters.
2) Proper weight for the application.
3) Quality product from a well known manufacture.
4) Whether is is Synthetic or Mineral. Synthetics will allow longer change intervals and have less changes in thickness over temperature ranges. They will also tend to provide better protection when pushed beyond normal operating parameters (i.e. engine overheating, lube failure, turbo motor). There is far more than just a black and white mineral v. synthetic. There is the underlying question of what are synthetic oils so you have to ask questions like what is a Group II+ oil, is is really just "mineral" oil? What about Group III hydrocracked oils which can be marketed as synthetics in the US but not the rest of the world? How about Group III+ synths? Group IV PAO's? Perhaps Group V esters?
I again strongly encourage anyone interested in further information to read the Oil FAQ on the 80 forum and visit bobistheoilguy.com.
I'm with you. Mobil-1 site list a number of units with factory fill on engine but none with gear oil factory fill.
Some good links for more information ...
Automotive Gear Oil Technologies API GL-5 - Clearing up the confusion (from Lubrizol)
Automotive Gear Oil Technologies - SAE J306 Specifications (From Lubrizol)
Based on some of the information in the above link it seems possible that Toyota spec'ed 90 weight for the diffs (but 75w-90 in the T-case) because many 75w-90s were lower in viscosity than optimum for the gear case while the 90 straight weights were higher in viscosity.
Hypothetical/Theorectical example -
SAE J306 allows a 90 weight gear oil to be between 13.5-24.0 cSt at 100 degree C.
Assume for arguement that gearcase optimum viscosity was at 20 cSt.
If the multi-weight oils (75w-90) were fomulated to 15 cSt-100deg (Example: Mobil1 75w-90 = 15.2 cST at 100deg) and the 90 straight weights tended to be formulated at 20 cSt-100deg (Example: Fuchs Titan Super Gear 90 weight = 18.4 cST at 100 deg) . Both would still meet the 90 weight requirement at operating temperature for the SAE specification but for the majority of users (and warranty holders) the straight 90 would bring them closer to the ideal viscosity for their LC.
Lubrication Theory and Practice (from Lubrizol)
The best source I've found for general lubrication information. (WARNING : this link contains scientific formulas and other scary math content.)
Automotive Gear Oil Technologies API GL-5 - Clearing up the confusion (from Lubrizol)
Automotive Gear Oil Technologies - SAE J306 Specifications (From Lubrizol)
Based on some of the information in the above link it seems possible that Toyota spec'ed 90 weight for the diffs (but 75w-90 in the T-case) because many 75w-90s were lower in viscosity than optimum for the gear case while the 90 straight weights were higher in viscosity.
Hypothetical/Theorectical example -
SAE J306 allows a 90 weight gear oil to be between 13.5-24.0 cSt at 100 degree C.
Assume for arguement that gearcase optimum viscosity was at 20 cSt.
If the multi-weight oils (75w-90) were fomulated to 15 cSt-100deg (Example: Mobil1 75w-90 = 15.2 cST at 100deg) and the 90 straight weights tended to be formulated at 20 cSt-100deg (Example: Fuchs Titan Super Gear 90 weight = 18.4 cST at 100 deg) . Both would still meet the 90 weight requirement at operating temperature for the SAE specification but for the majority of users (and warranty holders) the straight 90 would bring them closer to the ideal viscosity for their LC.
Lubrication Theory and Practice (from Lubrizol)
The best source I've found for general lubrication information. (WARNING : this link contains scientific formulas and other scary math content.)
Last edited:
... There is no such thing as multiweight tests, and the weights of oils that denote thickness have not changed in years.
There are standards that oils have to meet for the SAE viscosity designations. Whether oils meet those standards is detirmined by tests.
The Automotive Gear Lubricant Viscosity Classification - SAE J306 was updated in June 2005 in order to provide for the more precise classification of gear oils.
From Lubrizol ...
In June 2005, SAE revised the J306 Automotive Gear Lubricant Viscosity Classification Standard to narrow the range for two viscosity grades and create two new ones. Under the revised standard, the upper limit on kinematic viscosity for SAE 90 gear oil drops from 24.0 cSt at 100°C to 18.5 cSt, while the maximum viscosity for SAE 140 drops from 41.0 cSt to 32.5 cSt. Two new viscosity grades were introduced to cover the upper end of the narrowed classifications. SAE 110 comprises the viscosity range 18.5 to 24.0 cSt, and SAE 190 defines the range 32.5 to 41.0 cSt.
I take back what I said above, I think you were just being lazy with your terms based on your two later posts. Damm SAE, going and revising the breakpoints for grades since the last time I looked.
BTW, for those that don't know Lubrizol is the company that makes the additive packages used in virtually every brand of oil sold in the US.
But what of my theory that Toyota may have spec'd SAE 90 (1998) to get a cSt at the high end of the old viscosity range.
This might suggest going with one of the new SAE 75w-110 gear oils.
This might suggest going with one of the new SAE 75w-110 gear oils.
I doubt it. I think what you will find is that it has been that way in the manual for years and has never been changed. Manufactures are very slow at getting these things done. To give you an idea, BMW USA has recommended Mobil 1 5w-30 when you can't get their factory oil for the past 10+ years. BMW USA has never gotten the message that the 5w-30 meets none of the their requirements (ACEA A3, BMW LL-98, BMW LL-01). Mobil 1 0w-40 does meet the requirements (explicitly listed as a BMW LL-01 oil) but if you call the BMW tech-line they draw a blank. The 0w-40 has only been widely available for more than 5 years in the US.
Cary,
Most of my info came from the articles on BITOG. They state that:
1. typically about 20% of an oil is additives;
2. viscocity decreases as temp increases;
3. protection of an oil as the additives wear away becomes more like the lower number in a multi vis (e.g. the 10 in a 10w-30 oil);
4. mineral oils have difficulty attaining the multivis properties such as 10W-30, so they add additives to boost the performance at the operating (higher) temp;
5. For longer oil changes, pick an oil with a closer multi-vis because it will have less adverse impact as the additives wear (e.g. a 10W-30 vs a 5W-40);
6. gear oils do not have to deal with the combustion byproducts, so they have less antioxidants and more barrier protecting additives;
7. true synthetic oil bases have properties that make them perform like natural multivis oils (selective properties of specific chemicals for the base oil);
8. the manufacturer selects specific additives to custom match the properties of the base oil so as to meet the required spec for the oil, so adding additional "additives" can counter the custom design of the original oil additives with unexpected negative results;
In my posts, I see I confused applications between gear oils and motor oils. In general, the 75W-90 gear oil is equivalent to the SAE 90 for most applications. In my case, the Redline 75W-90 gear oil is a synthetic so even if I used their MT90, it would be the same base oil, though I believe the additives have differences.
But back to the original question, using 75W-90 M1 should not be a problem.
Most of my info came from the articles on BITOG. They state that:
1. typically about 20% of an oil is additives;
2. viscocity decreases as temp increases;
3. protection of an oil as the additives wear away becomes more like the lower number in a multi vis (e.g. the 10 in a 10w-30 oil);
4. mineral oils have difficulty attaining the multivis properties such as 10W-30, so they add additives to boost the performance at the operating (higher) temp;
5. For longer oil changes, pick an oil with a closer multi-vis because it will have less adverse impact as the additives wear (e.g. a 10W-30 vs a 5W-40);
6. gear oils do not have to deal with the combustion byproducts, so they have less antioxidants and more barrier protecting additives;
7. true synthetic oil bases have properties that make them perform like natural multivis oils (selective properties of specific chemicals for the base oil);
8. the manufacturer selects specific additives to custom match the properties of the base oil so as to meet the required spec for the oil, so adding additional "additives" can counter the custom design of the original oil additives with unexpected negative results;
In my posts, I see I confused applications between gear oils and motor oils. In general, the 75W-90 gear oil is equivalent to the SAE 90 for most applications. In my case, the Redline 75W-90 gear oil is a synthetic so even if I used their MT90, it would be the same base oil, though I believe the additives have differences.
But back to the original question, using 75W-90 M1 should not be a problem.
If you call redline and speak with Dave Granquest (sp) he will explain that the MT-90 also meets the 75w-90 spec. The only redline oil that uses any vis improvers is the 5w-40 motor oil. This is because synthetics have a naturally flatter change viscosity curve.
Numbers 3-5 vary from partially untrue to flat out incorrect. Unfortunately you have to be careful on BITOG now as every bozo in the world seems to be there now. Look carefully to see who is providing the information. A lot is incorrect, but people like Molekule, TerryD, and Pat know of what they speak.
Numbers 3-5 vary from partially untrue to flat out incorrect. Unfortunately you have to be careful on BITOG now as every bozo in the world seems to be there now. Look carefully to see who is providing the information. A lot is incorrect, but people like Molekule, TerryD, and Pat know of what they speak.
Yes, I saw that in the redline literature. That is why I chose to do 75W-90 in the transfer case also. I just figured there must be some insignificant difference to market a differently named product.
I also agree on Molakule, TerryD, and Pat. Their comments help with the oil chemistry terms. I am not quite used to all the standards used in the industry, but learning.
Unfortunately, the info on BITOG was from the lube basics articles. After your comments, I believe they (3, 4, & 5) are exagerations to make a general point and get one's attention, but the illustration is predominately based on old technology. A highly refined mineral base oil selecting specific chemistry will have enhanced "natural" multi-vis capability because of containing less undesirable compounds. This means less additives required to meet SAE multi-vis specs. The synthetics are even better because the desired chemical properties can be synthesized using starting materials that lead to highly specific compounds with the desired properties. Obviously, the fewer the additives to attain multi-vis, the less the generalizations apply.
I also agree on Molakule, TerryD, and Pat. Their comments help with the oil chemistry terms. I am not quite used to all the standards used in the industry, but learning.
Unfortunately, the info on BITOG was from the lube basics articles. After your comments, I believe they (3, 4, & 5) are exagerations to make a general point and get one's attention, but the illustration is predominately based on old technology. A highly refined mineral base oil selecting specific chemistry will have enhanced "natural" multi-vis capability because of containing less undesirable compounds. This means less additives required to meet SAE multi-vis specs. The synthetics are even better because the desired chemical properties can be synthesized using starting materials that lead to highly specific compounds with the desired properties. Obviously, the fewer the additives to attain multi-vis, the less the generalizations apply.
You are well on the right path and have passed about 90% of the people on BITOG. As you well understand, the further we go along the harder it is to generalize in terms of Synth v. mineral. You will enjoy this panthlet by Chevron targeted towards oil blenders.
http://www.chevron.com/products/prodserv/BaseOils/gf4_faq.shtml
Cold weather implications
After reading this thread, I came away with the conclusion that if the temperature in your area swings quite a bit, synthetic might be the way to go. Where I am at, it gets really cold. Yes! Colder than Colorado. Before I do my diff oil change this weekend, I wanted to verify if it is okay to change the three oils - transfer case and the two differentials to synthetic 75w-90. It seems, from reading the different threads that is will be okay to do so.
My coworker was saying today that he has two similar ford trucks - one with synthetic and one with non-synthetic in the diffs. He says that when it is well-below freezing, the differentials with synthetic oil on them seem to move easier. Any truth to this?
After reading this thread, I came away with the conclusion that if the temperature in your area swings quite a bit, synthetic might be the way to go. Where I am at, it gets really cold. Yes! Colder than Colorado. Before I do my diff oil change this weekend, I wanted to verify if it is okay to change the three oils - transfer case and the two differentials to synthetic 75w-90. It seems, from reading the different threads that is will be okay to do so.
My coworker was saying today that he has two similar ford trucks - one with synthetic and one with non-synthetic in the diffs. He says that when it is well-below freezing, the differentials with synthetic oil on them seem to move easier. Any truth to this?
Jim_Chow
V8_Fan
Here, in AZ, it was 21F last week at night. In the summer, it's upwards of 110-115F. So since I want to use the same oil, synthetic is a no-brainer.
That is how I understood it too. Makes my choice easy now.
KathmanduCruiser - Synthetics do move easier in cold weather. They also protect better in high temps. Since I travel a lot in varying weather conditions, synthetics are a no brainer. Some claim to get better MPG, but I haven't noticed enough of a difference there to confirm that.
I have used other synthetics and blends for gear oil, but the price difference was not that much to get Redline this time - so my vehicles have Redline 75W-90 in them now. There is no get-up-and-go sluggishness in cold weather.
I have used other synthetics and blends for gear oil, but the price difference was not that much to get Redline this time - so my vehicles have Redline 75W-90 in them now. There is no get-up-and-go sluggishness in cold weather.
