Barrier

Hi All, I would like some opinions.
I am changing the rear end lube. I was planning on using 75W90 Synthetic and then I read somewhere about switching to 75W 140 Synthetic.
Does anyone have thoughts or opinions about this?
My car is not Tracked just normal Spirited Street Driving. I have a 1993 Convertible with the ZF Manual and 3.45 Posi. Rear.
All comments welcome and appreciated.
Barrier

hogandtow

when i bought mt 2013 silverado the locker would pop and snap at slow speeds so i switched to 75/140 and have never heard that noise again.

BOOT77

Might slightly hurt your mileage

Christi@n

80w90 should be required for you car.... My 95 has this weight

74w140 is for high pressure use, usually truck or suv

GREGGPENN

The 75w-140 (Valvoline) isn't as heavy as 85w-140...such as Lucas. I've used/felt both products. I've run the wider Valvoline for 5 years now and have no complaints about noise, chatter, etc... Is it better? IDK. I thought it a good upgrade after adding 100rwhp.

Can't see that it will hurt. Could help with the extra sheering forces.

That said, multi-viscosity oils "settle" into a narrower range after a bit of time. So the "base" stock might be a bit thicker...though I couldn't feel it. I've run the Valvoline versus the heavier 85w-140 Lucas in my 4x4 and can tell the difference in cushioning. Lucas quiets more.

DGXR

Yes you can use the heavier 75w140 stuff without any troubles, although I'm not sure why you would want to. The heavy gear oil is for high-horsepower or severe service applications. As long as the car is serviced regularly, it's not being raced or used for extended high-speed driving, I suggest the 75w90 synthetic fluid you were planning on using. Whichever fluid you choose, be sure it has the LSD additive or put some additive in when refilling. Hope this helps you.

A Peter C4

The 2 most popular options are Mobile 1 75W90 or Valveoline Synpower 75W140 both synthetic limited slip spec.

383tpimachine

Lucas 75w140 in my setup.

A Peter C4

Lucas 75/140 syn. also very good and limited slip compatable

Barrier

Thanks Everyone!
I am going with the 75W90 for now. That seems to be sufficient. Perhaps next time the 140.
Interesting I found a post of mine from 2002 where I went the same way in my 1986 C4. I had forgotten about it. That was before LSA was added by Mobil. I had to add it back then.
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WVZR-1

It could be considered "wise" to use the LSA in addition to the choice you've made. Do it now when it's easy OR do it later when it's a nuisance!!

Barrier

WVZR-1,
Good Idea. Since they include it in Mobil1 would you think 1 would be sufficient? Back then I added 1 before they included it. And it worked fine.
I have read that more does not matter but it seems to me adding much more would kinda negate the "Limited" part and make it "Slip".
Hmmm...
thanks
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ddahlgren

I have always believed that lubricants and viscosities were specified for a new or nearly new car or truck with minimal wear. A C4 is an old car and most have 50k or many more miles, add to that things wear and clearances get larger. I see no crime in running a higher viscosity lubricant to help with the added clearance. Even simple things as the engine calls for 10-30 and I use 20-50 and oil pressure much more stable at 75k miles and do let the car warm up before getting rough with it and seldom drive below 40 degrees but even that 20w part easily covers that. I run plain Castrol engine oil and change it every 3k or 1 year and never look back. Light low viscosity lubricants are used for only 2 valid reasons being in my mind to squeeze out another .5 mpg or 4 hp. and I ma in for the long haul don't care about either just not having to open the hood to play around for a self inflicted wound.

A Peter C4

I believe the LSA helps the diff. to slip so on corners the rear wheel will not cheep or spin one tire in dirt,loose gravel but only so much before locking,i/e limited slip. I can't find any info on change interval in owners manual,but I think at least every 100,000 miles, maximum.

Tom400CFI

I don't know about that reasoning; I run 5w30 in all my cars (what they recommend). My truck has 291,000+ miles on it and it's oil pressure is both "stable" and the same as it was when I bought the truck with 80k on it. I'm in it for the long haul too and the OEM recommended oil has worked way better than good enough.

I'm not saying there is something wrong w/your choice...just that it seems that you're trying to solve a problem with your 20w50, that doesn't exist.

A Peter C4

Check out site 540 RAT tech facts, about engine oil, very interesting read ,it's on a forum post also. I myself always thought heavier oil better protection but after reading this article I think factory fluid recommendation should be followed but then to each his own. That being said I do believe in useing synthetic fluids in all of my applications except brake fluid.

Barrier

Hi Peter,
Why not Synthetic Brake Fluid?
You are referring to DOT 3 and or DOT 4 Synthetic not Silicone right?
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ddahlgren

20w-50 most closely match the temperature range I drive the Corvette. I use lighter oil in the 4 door sedan I use year round for work.

Tom400CFI

Huh. You live in CT. You have about the same weather and temps that I do....although you don't have Lake Powell. I've pulled my boat up out of there with temps over 110* so many times...


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ddahlgren

20w-50 is appropriate for between 20F and 112F and I keep the Corvette in a heated garage so never sees less than 50 unless warmed up in the fall for a ride then back in. This has been more than casual thought.