effect of burning trans fluid
 

Not Porsche related but anyway.

I have a Mazda B4000 (Same as Ford Ranger drivetrain) with Auto Trans with 346k miles. It's running fine, but I have to add Trans fluid to it quite regularly, about 1 quart every 300 miles There are no drips after parking, no fluid drips or wet spots under the truck that would indicate it's leaking out. Yesterday, while checking everything, I noticed some rubber vacuum connectors seemed to be wet and swollen from saturation in fluid, enough that I was worried there would be a vacuum leak there, so I replaced them. They went to the intake manifold, and should not be getting any fluid whatsoever there. Also connected there is a vacuum tube which runs down to the trans.

If I was sucking Trans fluid into the intake manifold, in essence, wetting the rubber connectors and then burning the fluid, wouldn't there be a telltale smoke trail or sooty exhaust pipe as evidence? Or would the trans fluid burn cleanly?

It's been doing this for some time now and is baffling me. Anyone have some advice here?

BTW, just had the truck emission inspected and it passed with lot's of room to spare.

Weird, but I suspect a quart in 300 miles is probably not going to be a perceptible thing, even if you're burning all of it. 4 quarts per gallon, assume you're getting 20 MPG (give or take) is 300/20 or 15 gallons of fuel burned to go that distance, or 60 quarts so you're talking a <2% contamination. You probably wouldn't even notice it, although possible.

It's not doing it any wonders. I would get it fixed. It sounds like the diaphragm in the modulator valve has a hole in it.

On the up side, you have stumbled upon an old used car salesmen's trick (one of the few that actually work). Trans fluid has all kinds of stuff, other than oil, in it. Friction modifiers, solvents to eliminate gumming up, and anti - foaming agents.

The friction modifiers will add just enough friction to let the rings get a "bite" and will usually re-seat themselves after a while. The solvents will burn off leaving the combustion chambers spotless (seen it in a few engines I've torn apart).

With 346K miles it might have done it some good. I'd still get it fixed though. It's probably doing wierd things in the transmission.

The old Ford auto transmissions used a modulator valve that ran off manifold vacuum. When that diaphram ruptured, you would suck trans fluid into the engine. The fogging was incredible out the exhaust. I literally stopped traffic once in a 1980 Bronco. Everyone thought the truck was on fire. Any hint of trans fluid odor at the tailpipe?

Edit: Oops... didn't see lm6y's reply so I'm a little redundant. ;)

+1
Vacuum Modulator.

A popular technique among the rotary crowd is to put a squirt of trans fluid into the park plug hole of the rotor housing and rotate the engine without firing it and letting the trans fluid soak throughout the engine internals.

After 24-48 hours of sitting you fire it up and run it like hell burning off the fluid. (lots of smoke) Then change out the plugs and the engine will run like new. This was done to very high milage engines to restore compression and get rid of excess carbon build up. Trans fluid is VERY high in detergents and really cleans things up.

You probably have a very clean engine inside now.

Cool, I'll change out the Modulator then. And check the results. Maybe I'll run some fluid thru my other high mileage cars.

Thanks for the good advice.

Many people recommend running a quart of ATF in diesels every now and then. I've done it a couple times, can't say I noticed a huge difference.

Does it have a cat covertor?
That's what I would be the most worried about. If it's burning trans fluid (which is basically a 5 to 10 weight oil with all kinds of additives) I be worried about it clogging the cat or fouling the O2 sensor.

+ eleventybillion on the vacuum modulator.

Or, just suck on the vacuum line, and see if it pulls, or you get a mouthful of ATF.
Spit. Don't swallow.

I purchased a dead Turbo RX7 for $900, trailered it home, tried to start it, and it would not, then I did the ATF thing to it and let it sit for 3 days. It fired right up and I drove it 70 miles that day. I guess I should have said, its a popular trick to do with dead Rotary engines. Your results may vary.