Rear axle differential. SAE 90 vs SAE 80W140

[Tourist]

Hi. I have a Isuzu Trooper and the manual calls for either SAE90 or SAE140 or multigrade SAE80W140 in the real axle with LSD. The manual said multigrade like 80W90 are only suitable up to ambient temperature of 30 deg C. The ambient temperature here is 35 deg C and I have a few concerns.

1. Are synthetic like Redline 80W140 better then plain quality dino SAE90 from Castrol or Caltex?

2. According to Redline webpage, it says the 80W140 is slightly less efficient. Here's what it says "Generally used in commercial trucks which will climb long, steep grades and some racing applications where power is not critical. Generally 0.5% less efficient than 75W90. Can also be used in differentials and transmissions where excessive noise is a problem and limited-slip differentials which vibrate excessively when turning a corner. Exceeds API GL-5."

3. The front axle calls for SAE80W140 only. If I am buying the Redline 80W140 that's suitable for LSD, can I use that also in the front axle as well?

Would appreciate your views. Thanks.

 

[ConfederateTyrant]

I personally would say Redline, or any synthetic gear oil, is going to be better than dino SAE 90. I personally don't see any harm in using 75w-140 in any of those applications, the only inefficiency is that you'll be using a thicker gear oil, which may (not necessarily) slightly lower gas mileage.

Since you're given multiple options, a synthetic 75w/80w-140 would be a good choice, in my opinion.

 

[KBFXDLI]

If you call the oil tech Dave at redline he will look up your vehicle and give you the correct application. But the redline oil will be better than the dino 90w.

 

[ccs v2.0]

In Malaysia? What's the coldest temp the Trooper will ever see, 28*C? Go with 80w140 syn.

 

[INDYMAC]

Here's a gear oil test done by Bob (BITIG).
http://www.bobistheoilguy.com/gearoiltest.htm
Sometimes you don't always get what you think you want. I prefer mineral based gear oils, but each to his own. I think Schaeffers and Lubrication Engineers make excellent SAE 90 GL5 mineral based gear oils that will meet your needs, but I suspect you won't be able to get either where you live.

 

[Tourist]

Thanks for all the replies. So I gather the majority prefers Redline. And no, I doubt Schaeffers & LE are available here.

But here are a few more questions that I am looking answers for.

1. Can Redline 80W140 LSD oil be used in an non-LSD front axle.

2. In the Redline website, it says there is another 75W140. Would this one be better then 80W140?

3. Do you need to do any special flushing out of previous old Mineral oil in the axle before refill with Redline?

4. Do you see any fuel consumption improvement with Redline vs Mineral?

 

[ConfederateTyrant]

Tourist,
1. Yes, Redline gear oils can be used in non-LSD applications, as far as I know.
2. The 75w would make it easier for cold flow capabilities, but a full synthetic 80w would still flow better than a mineral 80w. I'd go with whichever is cheaper.
3. Nothing really, just remove the cover, or drain plug, and let it drain for a while.
4. I couldn't answer this one with Redline, but I had an increase with Amsoil 80w-90 over Castrol 80w-90. I'm sure some others can answer this with Redline over mineral gear oil.

 

[KBFXDLI]

I didn't see that you were in Malaysia. You can log onto the redline website and fill out an application request and they will email you the answer.