Home | Mailing List | Specifications | Care and Feeding | Modifications | Vendors | Literature


ET's & ATF Levels

New 1/07/05

know I read this on the web site a year or more ago but google is not my friend at the moment.

Is there documented evidence that the AX4N saps less HP when not filled to capacity? How low is safe to go?

-- Mike Testa

there was discussion on the list, but I doubt I put it up on the site. Ron Porter I think had some comments along with some others. Maybe Uncle Scott K who archives everything can dig that thread up for you.


IIRC Ron had his filled to the bottom of the hash marks.. and found his car went faster. Not sure if Dudek and Mr. Waters {his forearms are bigger then mine only reason I call him Mister :oP} tired it or not.


That is precisely what I remember. Car was faster by a measurable amount when filled to the bottom of the hashes than when filled to the  top of the hashes. Doubt the difference was from extra weight as it would be about 3 pounds of fluid (about 2 quarts).  Ron Porter and Ryan Dudek we the main contributors of this info. I can dig through my archives if you like but I think they would be more than willing to chime in.


This is how the whole thing shook out:

A few years back people thought it was a good idea to run around with their AX4Ns filled 1 quart over full. The idea was to provide more fluid; less heat; more lube; less fluid sloshing and chance of the pickup being dry; I have no idea, it wasn't my idea. Ron tried this after one of the conventions (Tulsa?) and noticed that his car felt sluggish. That fall at the dragstrip, his timeslips confirmed that his car felt sluggish, with times in the 15.3-15.4 range. Remember, this was his '99 which spent days on end running 14.6-14.9. So, in the pits that afternoon, we decided to drain the extra fluid from the tranny. Ron and I both had drainplugs installed in the tranny pans so it was a simple unbolt, drain, replug operation. With only 30min elapsed and the tranny fluid gone from 1 quart over full to set at the bottom level of the crosshatch area on the dipstick, his car gained 3/10s and a few mph. Later on, when we were fighting with my car to get it into the 14s, we did the same thing, going from the FULL mark on the dipstick, to the bottom of the acceptable level. With that small (relatively) change, I gained 1/10 in the same manner (same day, same time, same track). I'm sure the people at Lapeer loved us, it wasn't like we had a drain pan with us. Anyway, moral of the story wasn't that we recommended running the car low on tranny fluid, just that we had best results running the car at the lowest acceptable level.

Ryan Dudek

With a motor the plan is a deep oil pan so the crank does not beat the oil in to ropey foam.

I wonder if the "low ATF" effect is the same, and could be better achieved by using a deeper ATX pan?

ATF changes volume with heat. If left high when cold it could puke up when run hard. If marginally low when hot it could be quart low when cold. Either is very bad.

All the normal disclaimers apply.


FWIW, the pan from a Lincoln Continental is ~1/4" deeper.

Ryan Dudek

It may be half a good idea. When one goes with a deep pan (oil or ATF) they also need a deep pickup.

If one uses a stock pickup tube with a deep pan they could under high G-forces uncover the pickup which would gulp air and lose its prime.

If that happens you can lose a motor or ATX in a few feet when it runs dry.

One might also check B&M and other aftermarket ATX companies for deep pans with extended pickups.

I don't think this is a s fruitful an investment as a full Doug Lewis rebuild with shift kit.


2 qts.. low is definitely on the wrong side of safe. Negligible effect on HP, but you'll eventually feel it in your wallet and pride.

On the bright side, they can't be that delicate. My ATX after running at least 300+ highway miles at least 1 qt. low and ending up fully 2 qt. low at destination still works after an ATX flush & fill. Now for how long, who knows. The only 2 after-effects I can detect are very slight amount of particulate in the fluid after 300 miles of hilly Interstate (still Mercon V red though), and a very, very slight binding until the car fully warms up. These are both nuance level and if I didn't know the car so well would be easy to overlook. No slipping or slamming yet. My car's ATX had 56,700 miles or less on it so maybe that's the difference between functional and destroyed and a higher mileage ATX wouldn't have survived.

On the disturbing side, I discovered that on this particular car it's very easy to get a false high level on the dipstick about 15% of the time. Park slightly downhill and that's good for 1/8" error. Check immediately after it's been driven and it will also read high. Maybe the dipstick is bent or something. I don't have another SHO to compare to. But this stick tends to pick up fluid from the wall of the tube or something about 15% of the time so I learned to have the car level, leave it sitting idling at least 10-15 minutes after driving, and take 3-4 fluid level checks to make sure it's right.

Hope this saves someone else $3000 or $4000.

Amy Sheetz
 '98 black

That is a "maybe" situation. I ran my '99 at Road Atlanta when it was 2 months old with 2K miles, and at Hallett two years later, and never overfilled the tranny. It performed just fine.

Never overfill the tranny.....no advantage, and the car runs slower.

Ron Porter

You also run the risk of 'sloshing' when you overfill, which is essentially air bubbles from the fluid contacting moving parts that it wouldn't normally. This is very bad for an ATX!! Better to go a touch low actually.

Dave Garber



Contact Information