Manual trans fluid level
 

My Cavalier's Getrag 5spd has a small annoyance. It growls loudly at low RPMs because of the relatively rough power delivery of the 4 banger. I believe some Opels have this transmission too and they have similar issues. Otherwise, driveability is wonderful and at 120K, all synchros are good as new.

GM's recommended fix is to add additional fluid. The standard fill is 1.8 quarts of automatic transmission fluid, I've got 6 in there to quiet it down. There haven't been any ill effects after 30,000 miles. Shifting effort increased a bit, probably due to the fact that the synchros are submerged, but that's it. Would you guys expect substantial gains from going back to 1.8 quarts?

I'm confused. You've got 1.6 instead of 1.8 quarts? I'm not sure how the transmission would hold a full 6 quarts if it's made for 1.8? (maybe i'm reading wrong?)

I don't know about any substantial gains from going to 1.8, however, using better fluid (like a synthetic if your tranny is made for or can use it) will help keep those synchros alive longer as long as you are shifting nice and smoothly. Other than that just make sure to keep it flushed at your regular intervals with good fluid. I flush mine usually a season early just because I prefer preventative maintenance.

I talked to two of the engineers at work (I work for an industrial gearing company). They said you are definitly loosing some power due to the extra oil in there. One said its not impossible that you could be loosing 2 horsepower through the box. At highway speeds 2 hp is a huge hit. However, both of the engineers were very concerned with the thermals of the box. The extra oil is going to really heat up the transmission. The increased heat not only breaks down the oil faster, but also pressurizes the unit beyond its specifications.

BTW, what kind of mileage are you getting in the Cavalier? You don't have a garage entry here...

To clarify, yes I do have six full quarts in the transmission. I expected a bit more drag from the fluid, but I would think the fluid would help dissipate heat away from the gears into the case of the transmission. Anyway, I find it hard to believe that the gearbox is any hotter than the engine it's bolted to. These engineers were aware that this is a manual gearbox right? Yes, my manual transmission takes autotrans fluid. Automatics build pressure during normal operation, but how would a manual do so? The gearbox is vented to the atmosphere.

Also, I am running full synthetic ATF (yes, it was expensive).

Right now I'm getting 20-28 city (depending on traffic) and 39 highway. The reason I don't bother posting tanks is because 95% of my driving is city, therefore my tanks are pretty unremarkable. Also, I'm not inclined to do any EOC on my 3.2 mile commute. Such short trips are hard on the engine as is.

The garage is meant as an aid, not a stage. It will still be useful if you can track changes in tank mileage, even if the numbers are not what you'd like. Ofcourse, personal preference is fine.

Excess MTF is going to sap energy from the engine due to increased viscosity. That energy has to go somewhere, which is generally heat. A lot of that heat gets absorbed into the engine block and sent out the radiator, but it probably increases the breakdown of the oil.

If you believe the engine will operate fine at 1.8l, you'll definately see a gain. To quantify that gain, do a towbar test at low speed to see differences in rolling resistance. Force scales are pretty cheap and it's easy to do.

- LostCause

LostCause pretty much summed it up. The engineers were aware its a manual transmission. If it is vented then you wouldn't have the pressure issue, but you would still have the heat issue. If you can live with the noise you will see gains by using less.

To counter the short trip problem I'd highly suggest an engine block heater. I would even use it in the summer. That'll help shorten your warm up time. With it in place I see no reason you wouldn't want to EOC. Personally, I would EOC even without the heater. What do you think your going to hurt?

This time of year, the engine heats up quickly, but in the winter, even after picking up my coffee at the drive through (I know, I know), the engine is only about 170F when I shut it off. Since the work commute is where most of the engine-hours are spent, it sees very little time at 195F, which is not very good for the engine or the oil.

I will drain out the transmission this weekend. As GM and Getrag have claimed, the growling is purely an annoyance and does not negatively impact the lifespan of the transmission. Mine looks like it could go 300K with no problems.

OK guys, I decided to drain the transmission early. I was planning on tinting my rear window, but I had to repair the defroster element, which needs 24 hours to dry, so I did this instead.

I got 2 quarts of Mobil1 fully synthetic ATF for $18, talk about wallet rape. I unscrewed the hex plug at the bottom of the transmission and I got six quarts of bright red fluid in the pan. It looked good as new, but I dumped it in the waste oil container and used 1.8 quarts of the brand new fluid to refill the transmission. A little bit of the growl came back, but not as much as I had remembered. Shifting effort decreased and everything seemed to be okay.

I decided to put down some numbers on my benchmark run to my favorite gun shop (can't have too much ammo). It's a 13 mile trip on a 65mph highway with very mild hills. I ran the test at 55mph steady state, in gear all the time, with the marker lights and DRLs, A/C off, AFR of 15.8:1 and tires at 44psi all around. AFR has been untouched for the past couple of tanks so I knew the SG was accurate.

I had acheived a best of 43.2mpg on this run before (return trip), but tonight my little 2.2L pushrod stomped its previous best with 45.0mpg to the gun store and 47.2 on the return trip!

A few caveats though... the back seat, rear deck and side plastic panels are out because I'm tinting the rear window, so maybe a weight reduction of ~40lbs is partially responsible, but either way, I was floating on a cloud seeing 46mpg for more than 2 seconds while coasting down a hill.

So like I said, after 30Kmi of mostly city driving, the fluid I drained was bright red, about the same viscosity as the new stuff, unburned and still had the smell of the new stuff. It didn't feel watery or otherwise compromised. I know what burnt fluid looks like, I've drained my automatic Cavalier before. That fluid was black and watery. I don't think the transmission sustained any damage, but it looks like the excessive fluid was a drag on it, making it act like a viscous coupling of some sort.

Sounds like a win. :)

JohnnyGrey, I see you just bought Mobil 1 ATF ... which seems to be working good. I am not surprised by your increased mileage numbers ... Mobil 1 products are formulated to be a tick thinner than other brands right out of the bottle. That's part of the reason people get such a good 'seat-of-the-pants dyno' result.

But, if you are looking to protect your tranny, I'd consider Royal Purple Synchromax. I'm generally not a big fan of their products, but I don't know of another purpose-made synchromesh fluid that is formulated as thin as (specified) ATF ... about 6.0 to 7.5 cSt.

It may even get rid of the howl as it has a better additive package for protecting against metal-to-metal contact.

There are the GM/Pennzoil syncromesh fluids ... but they are heavier at around 8.5 to 9.5 cSt viscosity. Again, one of these may get rid of your howl ... but at a cost of higher resistance (hydrodynamic drag).