Sorry to resurrect an old thread, but my searching has not found any clear answers.

So, I am curious...


Why the difference?
What is the risk of running the lighter oil with the Nitro Gears?

Background information: I have 165,000 miles on my original 3.73 gears with heavy loads and tons of towing. I had zero metal flakes on the drain at 75,000 miles and 150,000 miles. Last month, I upgraded to a Nitro Gears 4.56 gear set. I did the initial break in then drained and refilled with 80W-140 with the expected fine metal shavings a decent looking oil. I refilled it with Castrol 80W-140 per my mechanic's advice. Since then have put 2,500 miles on the vehicle, and I'm about to change the oil again just to ensure everything is okay. I have noticed that my fuel economy is way down. Power is up, but but I can't break 13MPG unloaded cruising at 55 MPH (I was as high as 18MPG fully loaded - not towing).

I changed the OEM factory diff fluid on my 2005 at 100,000 miles, and don't recall any issues - including pieces in the oil. It was black. Viscosity seemed thin. Hard to judge.

I used Valvoline 80/90 weight - which is recommended (with normal use)

4runner has always driven noiseless and fine.

I'm at 150,000 miles and may do a 6 quart DF soon. Rear-end holds total 12 quarts.

D/F is all Ill do. Hope 6 quarts Drain out - or I'll have to do it twice or call a dealer for advice.

I never changed this on any car I ever owned. Had a new GMC Jimmy - sold at 88,000 miles at ten years old.
two-year-old Cadillac - never touched it - 100,000 miles.

What is the manufacturers recommended maintenance schedule?

I think the posts here are way over maintenance on any rear ends (that don't tow).

The normal service interval for the differential is 90,000 miles so if you cut that in half you should have no issues. The severe service interval is 60,000. differential service - Bing

It's not so much the interval or the maintenance... I'm not having any problems with the new 4.56 gears at all. No noises, no problems on first drain/fill - I'm just having a problem with my fuel economy dropping so low since changing gears. That's why I'm trying to determine what I am going to fill up with at this next change. So far, most people I have talked to have not gone up to a 80W-140 after regearing.

A heavier weight oil is better for the longevity of the gears, and they don't really care about your MPGs.

I've been running 140w for close to 200k miles on my Nitro gears, but I wouldn't think twice about switching back to a 90w.

Yeah, since the initial post I have talked to a few guys about this, and 2 out of 5 people are running the 90W with no problems. However, like most people with 4Runners, they don't really care about their fuel economy. So, they don't track it. Although they have noticed the dash numbers are usually higher since regearing. Most of them have 285+ tires. I am running 255/75 C-Loads because I drive my vehicle so much, and I hate throwing away money in fuel.

Thanks for the reply!

When you cruise on highway now how do your rpm at 60 mph compare to previous with 3.73 gears? 3.73 to 4.56 is a significant change.

I think we went 120K on the last differential and transfer case oil change.

I am right about at 2,000 RPM at 64 MPH - with the 3.73 gears 2,000 RPM was about 71 MPH.

I had 1 mile on my TR4 OD when i drove it off the lot; dumped factory rear diff oil at 2200 miles and it looked dark gray and had a good amount of metal shavings. For me its cheep insurance!

I drained my rear diff from new every 10K

1) first drain at 10k was very dirty. Thick and grey

2) second drain at 20k was also grey and thick

3) third drain and 30k came out clear, not much grey at all

I plan to service the rear every 30k from now on.


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