Rear Differential oil 75w85??

My 2010 TRD 4X4 V6 manual states that the oil for the rear differential must be 75W85. Everyone here says that the manual calls for 75W90 oil weight.
Am I missing something here?

BTW 75W85 is almost imposible to find.

 

I have Redline 75w85 GL5 front and rear. I can get it not quite locally, it's 90 miles round trip, but it's also available on the internet. That viscosity is for gas mileage as far as I can figure. Pours like 5w20.

At first toyota said 90W, then 75w85 once the LSD diffs went bye bye ('09-up).

 

75-90, 80-90, 75-85 are all close enough that it doesn't really matter for typical use.

For heavy towing/hauling on a regular basis, I'd go up to 85-140 in the rear diff.

For wheeling, I'd go to 85-140 in both the front and rear diffs.

 

Manufacturer specs come from much thought processes from the engineers. They pretty much know what they are talking about. Yes, it is true that there is very little different between some of the ones mentioned, but I am curious the logic for running anything as thick as 85 - 140? The 140 viscosity is only good until the differential fluid is warmed up. Once it is at temp, the viscosity is 85, not 140.

 

This ^^^^, but I would add that if you use 85-140 it should be a full synthetic. I don't even know if there is a petro 85-140. The 140 number is a measure of how the oil behaves under severe heat. 85 - 140 synthetic is NOT a heavy oil like you would expect a 140 petro oil to be. Viscosity ratings are really outdated. They were developed for petro oils, but synthetics can operate at much wider temperature windows. The diffs in the Tacomas can generate a lot of heat towing. I tow a lot, so I run Redline 85-140 GL5

 

I gotta agree with bamatoy, engineers just don't just come up with the different numbers and have it be the same. There is a lot of thought and testing being done to figure out what oil is best for the purpose and vehicle.
Yeah I'm not going to go buy toyota's 60 dollar a quart diff fluid but I'll try to get as close as possible to the recommended oil.

 

The question is: what is the purpose? In the real world engineers design to a set of criteria that is handed to them by accountants, marketing wonks, and legal advisors. They swallow a lot of bitter pills. If engineers had their way, there would not be a 4cyl differential in a V6 truck. The rating specified for the rear diff oil was most likely decided by a need to provide the minimum lubrication that would get the maximum gas mileage. Making your rear diff run 250K miles is way down the list when compared to meeting EPA fleet efficiency standards or winning marketing points. I'm not saying there is anything wrong with the factory specs for typical use, but I would recommend applying a few extra brain cells if you use your truck hard.

 

This. And there is Petro 140, at least from Lucas. It's ECGS's recommended oil and been great for me thus far.

As badger mentioned below, auto engineers do the best they can within a price point set by accounting.

This.

Severe use (heavy towing, regular offroading) is not what ToMoCo's engineers spec'd the truck for in the first place. They spec'd it for most Tacoma owners who don't need a truck, they need a Camry with a bed.

That's why we have ridiculous shit like electronically actuated transfer cases, carpet floors, and undersized rear diffs.

When you start modifying your vehicle and/or changing its usage, the onus is on you to do the research, prepare the vehicle, and deal with the consequences.

 

I agree 100%...and I am currently using NAPA branded Valvoline 80w-90, available for $72 in the five gallon bucket at my local NAPA store.

Howard

 

Amsoil:http://ww2.amsoil.com/mygarage/VehicleLookupPage.aspx?FromIndex=1&url2=2010+TOYOTA+TACOMA+Z

 

One might consider reading through this before making unfounded statements regarding oil viscosity;

http://www.bobistheoilguy.com/motor-oil-101/
through to
http://www.bobistheoilguy.com/motor-oil-201/

Simply put, synthetic oil is a THICK oil that doesn't thicken up as much as it cools.
Mineral oil is a THIN oil with polymers that stretch out as it heats up to prevent it from thinning out as much.

In fact, an 85w140 synthetic is a MUCH thicker oil than 85w140 mineral. With the polymers in the mineral oil, this much thinner oil will behave much the same as an 85w140 when up to operating temperature.

How the oil flows at low temperature is a very poor indicator of how it flows at operating temperature.


As far as the "85" goes, this number is relatively unimportant when it comes to gear oils. In an engine oil, this relates to the temperature at which the oil is "pumpable". In a gear oil, there is no oil pump, so as long as the oil isn't as hard as a rock, which would be so ridiculously cold that you would YOURSELF turn to a block of ice in 5 seconds even wearing 15 parkas, let alone be able to start the engine, you'll have lubrication. It is OK if the gear oil resembles bearing grease, it will still lubricate a differential fine.

The "85" really only relates to operating efficiency at low temperatures. Not protection.

So what we see, is that a 75w85 is thinner at OPERATING temperature than an 85w140. You save fuel with the 75w85.

85 vs 90, 75w85 vs 80w90: Its a small change for sure, but represents a minor change in resistance and a marginal change in fuel consumption.

Its like 0w20 vs 5w20 vs 5w30 vs 10w30. A very very small change in fuel efficiency for the end user, but fleet wide, it might make a measurable change on overall volume of fuel consumed.


Now what's this about a 4-cyl differential being installed in a 6-cyl?
All the differential failures I've heard of have been the LOCKING differential, which is not an option for the 4-cyl. The 4-cyl gets the more durable OPEN differential.

I suppose that means that Toyota expects 4-cyl trucks to work harder than the 6-cyl's.

 

When I changed my oils in the diff and tranny (manual) at 30K, I thought the oil would look good, but wanted to run synthetic. The oil in the diff looked new, a nice golden color, and the tranny oil looked good but had a much darker, more worn looked to it. I thought it would be the other way around. I am running the Amsoil Severe Gear oil 75-90 in the diff now.

 

I also used 80w90. It was available in the quantity I needed. I haven't had any trouble

 

Is 75w85 hard to find. Almost everyone here recommends or uses 75w90.

 

None of my statements are unfounded. Maybe you should read them again.

First of all, there is no "normal operating temperature" in a differential. The temperature is unregulated and directly relatedl to the load on the gears and the speed of operation. The ambient temperature plays into it too. The differences can be dramatic. A tacoma running around town might be lucky to hit 125 degrees in the rear diff. On the highway 140 to 180 is more typical. That would be within the operating parameters of 85-90 oil. You start adding extra weight to the truck or add a trailer and that temp goes way up fast! It can easily go as high as 220-230, and it is possible to push it over 250.

The reason it is a particular problem in the 4.0 is because the rear diff is undersized for the application, if you plan to use the vehicle as a truck. Locking or nonlocking has nothing to do with it, with regard to the subject of heating and lubrication, so don't confuse the issue. Both units have an 8" ring. The heat build up in these diffs is more critical because there is too much power pushed through them under severe duty with the 4.0. Toyota engineers left the rear diff unchanged when they went to the 4.0 because someone in marketing and accounting decided that the average Tacoma buyer just wanted a car with a truck style body. They come from the factory as an ultra-light duty truck with hardly enough load capacity to bring home groceries.

Ultimately, the point of the viscosity rating in a gear oil is to provide a certain film thickness, and to insure that the thickness does not go below a critical level at the extreme end of the operating spectrum. If you push that spectrum by adding weight, doing heavy offroad driving, or towing with this truck, you need the heavier viscosity rating. Installing lower gears will increase operating temperatures too.

 

Why the hell are you replying to me? WTF dude?

 

You should use quotes to avoid confusion, especially when you accuse people of making unfounded comments. Some of your statements seemed to refer directly to my post at least in part, and I was the one who brought up the issue of the rear diff being designed for a 4 cylinder, so . Who were you talking to?

 

In 2009, Toyota changed their front and rear diff oil recommendation to SAE 75w-85 in order "to improve the fuel efficiency."