Question?
How can transmission fluid get into my engine oil?
Background:
My wife drives a Ford Explorer with the 4.0 v-6 and an auto tranny. First odd symptoms reared up as transmission slippage. I checked the fluid level and it was low, so I added some, it worked much better. Honestly this itself really wasn't that odd, as I had had a fluid leak (however slight) for sometime now. The leak was due to the rubber lines at the transmission cooler becoming old and cracked in spots. Not a real bad leak, but enough that every so often we needed to add a little fluid. But now it seems it was getting much worse and over the next three or four weeks I was adding fluid constantly (it seemed) to keep it going. By then the thing really seemed to leaking a lot.
So, I pulled the Ford into the garage to pull the tranny cooler and change the lines and clean and check the cooler. Everything went well and I decided to go ahead and give it an oil change as well. I reached down to pull the oil dipstick and check the oil level.....HOLY SHIT! This CAN'T be right! The freaking oil level was way way way too high. WTF???
I drained my oil only to see almost three gallons of oil come out! So I started thinking... "how can my transmission fluid migrate in to my oil?" That seems highly unlikely to me, but really appears to be happening, it would also explain the comment that my wife made about her truck running sluggish and shaking sometimes (with her crankshaft swimming in that much oil, it's a miracle it would run at all).
Note to self, internet posters can be morons.
So I jumped on the ol' internet search engines to find the answers, why was the transmission fluid mixing with my oil? What I got was a handful of other folks that had had the same issue (two of them with Explorers!) that I had. They had posted their problems in automobile self help forums. The answers they got were outlandish, mostly stating in no uncertain terms that they were idiots - that it was IMPOSSIBLE to have the two fluids mix. One poster even liked it to air from your front tires leaking into your spare tire in the trunk. Over and over again I read postings of how these two fluids can not possibly mix. Well I've been working on engines for more than 30 years, and I damned sure know where to put my tranny fluid into, and where the oil goes. To be fair I did see one or two intelligent comments, but they were rare.
The Solution:
Since one of the only ways the two fluids could mix, would be if the vacuum line attached to the transmission was somehow sucking up fluid into the intake manifold - and to me this DID seem HIGHLY unlikely, yet the only possibility - I decided to run a little test. I dropped by my local motorcycle shop and bought one of those little fuel line filters for dirt bikes, the small clear plastic ones that act like little windows. I plugged that into the vacuum line right where it goes into the intake manifold. 24 hours and 50 miles later, low and behold the little plastic vile was full of bright red transmission fluid! Why the fluid wasn't just burning out the exhaust I'm not sure, I guess it has something to do with the way that the fuel injected intake manifold is designed as opposed to a carbed intake manifold.
The fix:
$24 automatic transmission vacuum diaphragm ( also known as a vacuum modulator valve ) , and couple of hours to replace the old one. I don't know exactly how this thing works, but some way or another the old one was allowing the fluid to be sucked up the vacuum line and into my engine. One other thing, I guess this is a part that rarely has to be replaced, for when I called Schuck's Auto to check on the availability and price of the part the folks there had no idea what I was talking about and could not find it anywhere in their system, Napa Auto, however, had it in stock, thumbs up for Napa!
So there's your answer. I've posted this as help to those few individuals that may run into the same problem. You're NOT crazy, it can happen, don't let the internet posters that may at times be morons convince you otherwise!