At a loss (transmission and differenial fluid change)

[originalcyn]

i changed my transmission and differential fluids about 2 weeks back and i'm noticing a loss of economy. i put in amsoil stuff because it was recommended to me, but as far as i know that should actually improve economy.

The other thing that changed was a fresh set of tires. i'm not sure if that affects anything or not, but i thought it was worth noting.

Suggestions?

[soundman353]

How much of a loss are we talking about?
There are a few other things that could have changed. First I would check to make sure the fluids are topped off. Second check the air pressure. Some thing else to consider is winter fuel and summer fuel. The gas/oil companies put different additives for the winter season. Here is an article about winter gas. http://www.zhome.com/ZCMnL/PICS/winterG ... erGas.html

[kimokalihi]

Yup winter gas brings mileage down a lot.

[Legacy777]

I would think the tires are going to affect it more than anything else.

The main thing that changes in gas between the winter & summer months is their vapor pressure. In the past, winter gas used to have an oxygenate added to help emissions, it used to be MTBE, and then was ethanol. However almost all metropoliton areas use E10 year round, so you're not likely to really see any difference with the oxygenate vs. no oxygenate.

[originalcyn]

Thanks for the heads up everyone. I heard about the winter gas/summer gas fiasco, but i noticed that a few years back gas stations always had up "maybe contain up to 10% ethanol" instead of only having it up in the winter. i'm pretty sure that changed to a certain extent, and if it didn't it was an interesting coincidence that they changed it right when i was doing my fluids. interesting, but not nearly impossible, lol.

Fluids were done professionally, so i'll ask my mechanic. he's my family's mechanic, first name basis all that jazz. absolutely love the guy.

The drop in economy is about 2 mpg. not much, really, but back to what it was last spring. since spring i've done an intake and exhaust. those seemed to help the economy a bit. i was averaging 20-22mpg in spring, but the few weeks of summer before the fluids change it seemed like i was getting 23-24mpg.

[originalcyn]

So i've been noticing something. My drive to work in the morning is about 15 minutes long. It use to be that when i was driving at about 65mph that my rpms sat around 2500. Now, for 3/4th of the trip, it sits at 2750, and then for the last 1/4 before i get to work, or before i get home, it sits at 2500. i'm not sure if this is related or not, but it sounds like it's struggling more than it use to until it gets in the 2500 range.

[WRX2FFU]

Is this an automatic? If so sounds like the fluid is not right. Slipping maybe? Usually they slip when hot unless it's low on fluid.

MT's are usually pretty forgiving on fluid level, needs to be full but....

Did you use factory recomended viscosities? Also if you did the diff is it a rear lsd? Some lsd's require different fluids, IE: friction modifier or not...

Did you put on stock size tires?

What car is this for exactly?

[gijonas]

Yeah sounds like your tires are a different size.

[James614]

If the RPMs are only higher for 3/4 of the trip, and then drop to normal, I'd say it sounds to me more like a torque converter that doesn't want to lock up when it's supposed to.

When was the last change done before this? I've heard of automatics that'll run like tanks on the factory fill almost forever, but when a well-intentioned owner does a change at 100K+ it suddenly starts to act up. Not sure if Subaru transmissions are like that though.


But I'm still leaning towards the tires making most of the difference you're noticing, different tires can affect economy by 2mpg or more easily.

[originalcyn]

Is this an automatic?

Yeah, it's an automatic.

Did you use factory recomended viscosities? Also if you did the diff is it a rear lsd? Some lsd's require different fluids, IE: friction modifier or not...

For the transmission i used this: http://www.amsoil.com/storefront/atf.aspx, which is what's recommended by AMSOil, and my mechanic. it seems to be a universal fluid.

For the differentials I called carter subaru and they said that the fluid should be 75w-90, so i used this: http://www.amsoil.com/catalog.aspx?code=FGRQT-EA.

Mostly i followed the spec sheet from AMSOil: http://www.amsoil.com/mygarage/ProductR ... U+LEGACY+A

Did you put on stock size tires?

I put on General UHP Exclaims. The wheels are from a 2002 WRX. They're not new wheels, just new tires.

What car is this for exactly?

Thought i put this in the first post, but apparently i didn't because i'm a spaz. it's a 93 Legacy LS.

Yeah sounds like your tires are a different size.

They are a different size then the standard wheel and tire for that year of legacy, but i was running the same set of wheels before with a set of falkens.

If the RPMs are only higher for 3/4 of the trip, and then drop to normal, I'd say it sounds to me more like a torque converter that doesn't want to lock up when it's supposed to.

Thanks! I'll ask around about this.

When was the last change done before this? I've heard of automatics that'll run like tanks on the factory fill almost forever, but when a well-intentioned owner does a change at 100K+ it suddenly starts to act up.

I'm not sure if it was the original fluid or not. I haven't done it before, but i got the car at 72k miles. The previous owner was an old man who was very meticulous about getting oil changes and other kinds of regular maintenance.

But I'm still leaning towards the tires making most of the difference you're noticing, different tires can affect economy by 2mpg or more easily.

Could be that the Generals are just more grippy than the falkens i guess. Though i do get a lot of squeeling coming around the everett mall exit when i jam into it versus the falkens.

Thanks everyone!

[James614]

A tire's grip isn't directly related to it's forward rolling resistance (fuel economy). Tread design, side-wall construction, rubber compound, weight, etc all play a factor.

[originalcyn]

Gotcha, that makes perfect sense.

[originalcyn]

So my tires were at 29psi but the max rated is 51psi. Who's running General UHP Exclaims with 2002 wrx rims? I'm curious what everyone else is running for psi. I think i'm going to go to 40psi. Anyone see issues with that?

[kleinkid]

At 40 the ride will be harsh, poor traction. Try 35 and if you like it that's fine, 34 should be is closer to what Subaru would recommend.

[James614]

On stock size tires, I keep my pressure at 37psi and get better traction than at the factory pressure. The ride isn't harsh at all, mostly just more noise. But not much. Unless I'm driving on snow/sand/mud/etc there's no reason to run the lower pressure, which trades of traction and fuel economy for softer and quieter ride.