Front & Rear Differential Factory Fill Low

They're designed to hold certain amount of fluid for proper lubrication and cooling. 30% underfilled is too low. Would you run your engine 2qts too low? Everything was designed with a purpose, even torquing bolts to specs

 

Do you fill your oil all the way up the high point on the dipstick?

 

The initial poster reported being approx. 13% low in the rear and 22% low in the front, assuming the numbers posted were correct.

The differential oiling and engine oiling systems are quite a bit different. Different enough so to not be directly comparable like you’re doing.

 

I've noticed less gear click in stop n go traffic between 1 an 2 to 1 and back 2 in very short periods of time

 

I think we need to define what "underfilled" means, since I don't think we are all on the same page.

Just because a spec sheet says the fluid capacity of the differential is 4.2 quarts does not mean that at 4.19 qts, the diff will overheat and self-destruct. There's a range of acceptable fluid levels, and the reality that is nobody here (to my knowledge) really knows the lower bound of what the acceptable amount of fluid is for safe operation of the diff. Is it 4 qts? 3.8? 3.5? 3? At some point, sure, if you go too low, there won't be enough oil to properly lubricate the gears and the diff will burn up.

IMO this is an oil service life issue. Less oil means it will need to be changed sooner since the protective additives will get consumed faster, and wear particles will accumulate faster.

 

I always have To just below by an 1/8 is what vhf I shoot for.

 

You know there's nothing wrong with not filling it that high right? It's ok you do it, but it's not required.

 

Yup Figured the extra volume within fill range could only be a positive to aiding engine longevity

 

I think they fill to 4 quarts, but 4 quarts just doesn't get it up to the fill hole on TRD OR's (can't speak of other models). 2016 was 1/2 bottle short. 2016 rear diff crapped out at 32K and they put a new diff in. They put 4 quarts in, but when I checked, it still needed 1/2 bottle to come up to the fill hole. 2020 picked up last week, was also 1/2 bottle short. It is what it is and it's probably not that big of a deal, with as many people that drive around 1/2 bottle short without diffs grenading. I could see putting in the other 1/2 bottle to act as a heat sink, but maybe that's not even that big of an issue with the TRD OR's since there's no air dam with perhaps better air flow?

Given that, YES. I filled the missing 1/2 bottle all 3 times.

 

I suspect changes to the driving characteristics being described are more likely attributable to a change in oil type than oil volume. Did you refill with the same type of fluid?

As for the specification itself, Toyota does offer a limited range for the capacity on the differentials (ranging from +/- 1.3% to +/- 3.3%). The capacity given is likely from dry. Their caution statement is much more generous on acceptability: “Excessively large or small quantities of oil may cause problems.” So how much is excessive? For that, we can look to the rear differential gasket recall instructions. In the recall, the oil is drained and the volume checked. If less than 2.0L is recovered, the differential is to be replaced. As this is a safety recall reported to the NHTSA, I suspect that value was carefully considered, and that there is a very low chance that a vehicle with more than 2.0L will experience differential failure.

Of course then the question becomes what is differential failure. From a safety standpoint it may not be the same as from a lifespan perspective. Again, I suspect Toyota and Tacomaworld’s opinions will vary heavily.

At the factory, the oil is likely metered from a gun and closed up. There will be a test and it is likely rechecked, but it will not experience the same inclination as it does during transport and driving.

Here are the specs from Toyota:

Toyota Genuine Differential Gear Oil LT 75W85 API GL-5

Front:
1.45-1.55 L

Rear:
A/T without Diff Lock (AC, DCSB): 2.85-2.95 L
A/T without Diff Lock (DCLB): 3.00-3.10 L
A/T with Diff Lock and All M/T (AC, DCSB): 3.75-3.85 L
A/T with Diff Lock (DCLB): 3.95-4.05 L

Gear oil to be filled to within 5mm of the fill plug.

EDIT: Worth noting: the 2.0L in the recall is for the A/T without diff lock.

Jeff

 

I used viscosity stated in manual and the brand redline. I think when it was new the driveline "feel" is similar to how It drives now after the diff fluid change. However; this might be a bit of the princess and the pea going on.

 

Great post!

 

Yes.

 

This is over reacting.

With Dodges you're supposed to be 1mm+ under the fill line.

But I'm sure your brand new truck drives better with your new fluid.

 

So I've ran through two tanks of gas (sam gas station\octane) since I changed the fluid in the differentials. The best (and pretty stable) running averages I had been getting was 19.7 to 19.8. Last two tanks are the highest I've been getting, 20.2 to 20.3. Exact same driving routine, and its actually been much colder as well. Can this be associated with the fluid change in the differentials? Nothing else has changed

 

I have not noticed a change in milage after changing out my diff fluid or transfer case fluid.

 

I like to fill my diff at 1/8" below the plug. A little less is no big deal, the biggest thing is the axle bearings. Oil need to get down there. Too little and they may suffer premature wear, too much and you may get an axle leak. I have seen both, so I know I'm fine just below the fill plug.

That said, you can actually feel the difference in rolling resistance after an diff oil change. Especially If it's a vehicle that you drive often and pay attention to its operational performance, therefore better mpg is possible depending on how much friction there was before.

Just my .02

 

Sure, it's too low. The rear end isn't going to grenade under the conditions stated though. An engine with 5-6 quarts capacity will likely run fine being two quarts low.... until you go up a hill or at 6000 rpm for an extended period of time. People design/build stuff with a lot of margin. They then put the measurements in the middle of that margin. We don't build things to be on the ragged edge unless you are doing something extreme like racing. Even then, they have margin.

 

That's interesting information, about 33% low is what they are worried about.

 

If your OP is correct, you're running thinner differential oil than what Toyota recommends. Less resistance = more MPG, but it also means less protection.

I don't like what if's, maybes and/or experimenting with expensive parts. If the manual calls for certain quantity of fluid I'll make sure it's there. If people want to experiment and ride with underfilled diffs, by all means just make sure to post back when new one is installed