I am in need of a bit of experience and knowledge. I have a 1999 3.4 AT 4Runner with 207k on it. About a month ago I noticed the radiator was leaking. I could not find the leak anywhere but it was very slow, But enough to drain the radiator, and overflow bottle. I filled it back up with DI water to see where the leak was but never found it. The truck is not my daily driver so I thru a can of radiator leak stop in it with the plans of replacing the radiator within the month. Yesterday I was driving it and it left me stranded. Basically it would rev up like normal but no go from the transmission in any direction (ie slipping?). I had it towed home and dropped the front rock guard thing and the 1 "nipple" that threads into the radiator (bottom passenger side) stripped out and the transmission line that runs to the radiator was dangling, and obviously dumped all the transmission fluid.

So at that point my thought was the new radiator, and hopefully when I filled the transmission fluid back up all would be good. But when I took off the radiator cap, I noticed the rubber gasket was "swollen" and about 1/3 bigger than it had been. I popped the cap off the overflow bottle and the hose that drops down no longer fits snuggly on the cap (its also "swollen") Neither the radiator or over flow bottle look pink but alittle milky, but Im thinking the ATF fluid mixed with the coolant and is causing the gaskets to swell. Which then means the coolant mixed with the ATF and ran through the transmission. But we'll just speculate and say that the radiator failed between the coolant and ATF sides after I filled it with DI water and the fluids mixed, but what if theyre just DI water mixed with ATF? So is it not pink and milky because there was no coolant and milky because the ATF mixed with the DI water?

How does the coolant affect the trans? and how does the ATF fluid affect the radiator?

Anyone have any insight or am I just looking at a new radiator and AT transmission now??

 

-update-

So I dropped the AT pan and there is no pink milky fluid. Just dark fluid. It does not smell burnt or anything.

Any thoughts? Just a new radiator and fill up the AT fluid??

AT fluid on white paper towel:


Trying to swirl it to see thru it:



Broken "nipple" from AT line to radiator:



Female portion where the "nipple" threads into (the threads from the radiator pulled out. The "nipple" is clean)



And "swollen" gaskets/hose:

 

That ATF fluid looks very tired. It should be red in color, not nearly black if the photo is accurate. It really does not matter if it's ATF or the DI water in the tranny...both have no business in the tranny and need to be drained and flushed out.

Have you searched for the strawberry milkshake threads to see how others flushed/dried the tranny out?

 

yeah Ive been reading all day about the milkshakes and the transmission fluid does not have the consistency of having water or coolant in it so I think I dodged a bullet there. The trans fluid has atleast 100k on it so Im not surprised how dark it is.

Im more worried about all the "swollen" gaskets and such up by the radiator, that has me puzzled.

 

Looks like the rubber just stretched from heat on an old cap.

Its possible that the o-ring on that broken nipple did not fail....if it did, strawberry milkshake for sure. Has any water separated out of the ATF sample you pulled?

 

Its really hard to tell. I have about 10 ounces of fluid I pulled out and looking at it, I cant tell if theres a small water layer on top or its just the meniscus ring.

 

Maybe that stop leak stuff you put in has something in it that swells rubber as part of it's "stop leak" properties.

 

The AT fluid doesn't look like it mixed with the coolant. There is always the possibility the PO used cheap or the wrong ATF when(if) they changed the fluid last. Buy 6 gallons of Valvoline high milage ATF (3 to refill and 3 to flush) from advance auto ($17 ea) and flush the transmission soon. Here's a link on how to do it. Dont get a power flush, not with that many miles on the clock. Of course, get a new radiator and cap and new coolant. Hopefull that will fix you up. Be thankful the transmission line blew off instead of allowing the coolant to contaminate the transmission. I'm guessing the dark fluid came from running empty. but who knows.

Trans flush

Only do 2Qts at a time. The fill spout is too small to keep up with the ejection rate. The pan should hold 4Qts, so fill it with 5 fresh Qts of fluid.

As for the coolant, flush out the stop leak. I'd guess the coolant was leaking out the same place as the AT fluid before the hose blew out.

 

That was one of my thoughts.

 

It sounds like the transmission fluid leak was from the loose hose, but the cause of the swelled up gasket and empty coolant overflow tank could be coming from an internal head gasket leak. the symptoms can be exactly the same, hydrocarbons, aka oil will cause the rubber gasket on the radiator cap to swell up, i would smell the inside of the radiator itself and in the overflow tank to see if its smells like exaust or oil, if so then it sounds like you have yourself a head gasket problem.

 

I would start with a transmission flush, then replace the radiator. Once its replaced, pressure test the cooling system. If i ever suspect hg, I pull the plugs out. That way if it fills a cylinder, you won't lock the motor. Has the water pump been replaced yet? Those to fail and leak. Look for coolant residue on the front of the motor.