75w-140 in a 5mt

[edian727]

so i just started at a lube shop last week. we didnt have 75w-90 today so my manager had me put 75w-140 in the trans of a 95 impreza, awd, manual 1.8l. I'm still pretty upset about it. is this gonna hurt the car?

 

IDK if he told the customer, but my guess is not. if this is really gonna hurt the car im gonna have to do something about it. kinda feel like i should anyway. how can you think its ok to put the wrong oil in without even knowing if its gonna work right or not? because i have no idea, and im sure he doesnt either.

[ronemus]

The viscosity of 75W-90 & 75W-140 is actually the same, so there should be no issue.  75W-140 is usually "synthetic" and more expensive, but longer lasting.

[czny]

Many years ago before I knew any better, I put a heavier viscosity hypoid lube in my 67 Beetle trans. Until the ambient temperature rose to the 90's F +, the heavy weight hypoid lube made shifting difficult as if the synchros didn't even exist. Got so bad I was double clutching to shift. Changed it back to  90W  hypoid rather quickly as it was worse in the winter.

Synchro cones brake the gears to match speed with clutch hubs for smooth shifting, so if the brass synchros are locked to corresponding gears by heavy lube, shifting would be sluggish.

Unless WA state has a region like the Great Victorian, Mojave or Kalahari deserts, I would say its a bad idea.

Edited July 1, 2017 by czny

[GeneralDisorder]

75w140 is often used for racing applications. It puts down a thicker film and will handle greater loads.

 

It may be slightly thicker when cold - the visco is a range and therefore even though both are 75w, the 140 will have a heavier feeling shift when cold.

 

The 140 doesn't flow as quickly so it doesn't cool as efficiently. In the world of a 95 Impreza this means basically nothing though.

 

It will work fine, all things being considered and will not technically harm the transmission. On the contrary it will provide better protection and a thicker film.

 

It may not work as well as the Subaru HPGO with the syncros. Not all (very few actually) 75w90 gear oils work well.... HPGO and Motul Gear 300 are the ones we use.

 

Don't worry about it. If it doesn't grind it will be fine. Better even.

 

GD

[Olnick]

I salute you for your conscience and for asking the question, edian727.  Good going!

[edian727]

thanks guys. especially you GD. all of our gl-5 syn. has limited slip aditive in it. im not sure exactly what kind of additive subaru uses though. i personally use redline 75-90 ns. its specially made for trans axles with hypoid gears. heard lots of subaru guys love it.

Edited July 2, 2017 by edian727

[GeneralDisorder]

Redline is ok. I didn't get as good of syncro operation with it as with HPGO or Gear 300. But many people like it. If it works for you that's great. 

 

The limited slip additive is in most of the gear oils these days. It is only required for clutch, cone, or plate limited slip style units. Most Subaru LSD's are of the viscous type and do no require any additive. A 95 Impreza will not have any limited slip devices other than the sealed 4kg viscous unit inside the center diff. 

 

GD

[carfreak85]

OP, where do you work so that we can all avoid going to this place?  Despite the laissez-faire attitude that some folks here have about using the wrong gear oil, I would be livid if I found out your shop did either of the following:

 

A) put the wrong weight in my transmission/diffs

put gear oil with LS additive into a transmission without LSDs, or one with sealed, viscous LSDs.

 

The older a car gets the more worn the syncros will be.  After a certain point (~199,000 miles in my Tercel 4WD) if you don't have the correct gear oil, the transmission will start to get very grumpy and difficult to shift without griding gears.  I'm actually dealing with this problem with my Tercel right now, I have to double clutch and double declutch 3rd gear because I replaced the trans fluid with whatever Autozone had, in a pinch.  I finally bit the bullet and bought the correct Motul GL-4 lube for that transmission, none of my local shops carry the correct weight or blend on the shelf anymore.

[GeneralDisorder]

You're real problem is that it's a tercel 4WD transmission..... several seemingly desperate individuals have nearly begged me to attempt a rebuild on one of those nightmares and after seeing one in the back of a truck..... no way. Too obscure and overly complicated. 

 

Race teams change oils and gear oils all the time depending on conditions and the desired performance. Even manufactures list multiple options for different environmental conditions. 

 

As I said - IF it doesn't grind, it will be fine. 75w140 encompasses 75w90 entirely in its range. If you talk to oil engineers this is much more important than the actual numbers. Also how it performs.... If 75w140 has acceptable performance then it will be fine as its lubrication properties are actually better than 75w90. If it doesn't perform then it needs to be changed out. 

 

I wouldn't guess it shifts very well cold and it might cause grinding. But if it doesn't then it will be ok. I suspect it's probably not the best drive experience though. Based on my experience. 

 

GD