G1 Q45 H50 Rear Differential Fluid

[SFBayQ45]

What type of rear differential fluid does the 1990-1996 Q45 require? The owner's mannual does not referrence the recommended gear oil. What brand and weight do you use? How many quarts does it take to do a complete fluid exchange?

[troy3399]

The Differential Fluid Capacity1 1/3 Quarts

The Differential Fluid TypeGL-5

Application:32 degrees to 104 degrees Fahrenheit

Gear oil Weight = 90

[qship96]

Use a top quality synthetic gear oil. I have used Redline 75w-90 and many others here use mobil 1 75w-90 with good results- I change mine every 25,000-30,000 miles and so far the differential is still quiet at 230,000 miles on my 96Q.

[maxnix]

I have used Royal Purple, Amsoil and M1 synthetics in 75W-140 weights for summer in TX.

[DrewQ45]

What type of rear differential fluid does the 1990-1996 Q45 require? The owner's mannual does not referrence the recommended gear oil. What brand and weight do you use? How many quarts does it take to do a complete fluid exchange?

Less than 2 Qts of 80W-90 GL 5 fluid. I believe I used valvoline synthetic last time. Just pour it in till it overflows. Warming the fluid helps make things a bit easier.

One thing, be sure fill bolt is removable before opening drain bolt.

[SFBayQ45]

I appreciate all the feedback guys, however I'm still a little confused. With the exception of the extreme weather condition in Texas, some of you use 80W-90 GL 5 fluid while others use 75W-90. What is the best weight to use in California. Or rather, what is the recomended gear oil type period?

[maxnix]

Or rather, what is the recomended gear oil type period?

RTFSM!

In NoCal, go with 75W minimum.

[qship96]

Earlier this week I had my diff fluid replaced- I thought I would step up the viscosity a bit due to age of differential{231,000 miles} and custom blended a 75w-115 mix by using 1/2 75w-90 and 1/2 75w-140 Redline gear oils. Magnet on drain plug showed small amount of metal fur sticking to it,and the old 75w-90 oil came out looking still translucent with 25,000 miles on it.

[maxnix]

No harm in going 75W-140.

[qship96]

Roy Howell and Dave Granquest of Redline both thought the idea of my creating a 75W-115 mixture would be a good way to slightly increase viscosity to account for age/wear without stepping all the way up to the 75w-140 and taking the extra hit in power/fuel efficiency-

[maxnix]

No "extra hit" with 75W. I am quite frankly surprised at their advise.

[Q45tech]

Important to understand differential friction [drive train loss] at different temperatures with different viscosities.http://www.nagtroc.org/forums/....htmlScroll to middle to see 290F is not uncommon on track or in mountains in summer.http://64.202.180.37/files/kits.pdf

For a Titan: " Cruising at 70mph the diff gets to about 170-180. Cruising in West Texas at 85mph gets the temps to about 210-220, these numbers are when using Mobil 1 Full Synthetic 70W-140 Truck and SUV Gear Oil."

[qship96]

No "extra hit" with 75W. I am quite frankly surprised at their advise.

Say what???? the 75W-140 gear oil is much thicker at both low and high temperatures than the 75W-90, resulting in less MPG and power transfer efficiency- study the link below to see the differences at both 40 and 100 degree C. temps! http://www.redlineoil.com/pdf/5.pdf

[Q45tech]

What is right for one in a HOT southern summer is often wrong in a COLD northern winter.

If you want perfection you must use 2 different grades and chage in November and April....................assuming you do race and do exceed 212F.

[goody90q45]

......What is the best weight to use in California. Or rather, what is the recomended gear oil type period?

I use Mobil 1 synthetic 75W-90 in both my Q's. The same weight will work fine for your Q year round. Easy to switch to synthetic since there's no flushing required.

[Q45tech]

Sp very very easy to use your IR Temperature gun to point and shoot at differential after you stop to get an idea of the various temperatures you might encounter with your driving style.

The worst friction losses occur from stop to say 10 mph until the lube gets flying around, these can be 3-4% then stablize at 1%.

At a steady cruise the engine is only producing 25 HP so 1% losses are meaningless 0.25 HP [is a small amount of heat say 3,000 BTU] at peak speed 3 HP is 36,000 btu.

The temperature gain allows you to easily calulate the friction losses net of any fin cooling vs speed.

[DrewQ45]

I appreciate all the feedback guys, however I'm still a little confused. With the exception of the extreme weather condition in Texas, some of you use 80W-90 GL 5 fluid while others use 75W-90. What is the best weight to use in California. Or rather, what is the recomended gear oil type period?

Get whichever is cheapest and easily found. It won't make any difference. San Fran weather doesn't ready see any extremes year round. Just change it every 50K or so.