This is probably an easy one for most...but I've been trying to figure out which one of my transmission lines is the feed, & which one is the return? I can easily identify the two lines, both coming from the radiator (one high & the other low), but I don't know which is which! Is there a test or something I can do to find out, or does someone w/the same vehicle already know?

I have a '98 ZJ, 4.0 I6

yea theres a test put the jeep on jack stands, disconnect one of the hose, start the jeep and place it in drive. if the fluid comes out of the lines then thats the feed line, if it starts drianing out of the radiator then thats the return line.....lol just fucking with you, i don't knwo which ones which but that would be one way to check.

Very funny dksob81, I see you have jokes, I like that! I'm not crazy enough to take your advise on this one though! I'm getting ready to install a tranny temp guage & I would like to install it to the feed line. I would hate to have just choose a line by guessing.

The line coming out of the front of the tran is to the cooler and the return is towards the back of the trans.Also the feed line has an anti drainback valve between the metal line and the rubber part

The trans coolers are one way loops, in that the fluid will only travel one way. Undo both lines and put some compressed air to one of them. If oil sprays out the other line of the cooler, then you know you have the outlet from the trans. I just rebuilt my 42RE and was trying to flush the coolers (radiator cooler and external cooler) with cleaner, but it only flowed in one direction. I called a mechanic friend and he told me that it is one way so the fluid doesnt drain back into the tranny every time you shut off the engine. This will tell you which line is the feed.

Rich

Thanks for the feed back, I was definitely confused on this one! I'll try the compressed air & take it from there.

Thanks again

top rad connection - feed. bottom -return. think gravity. Ull push high pressure air through your tranny? Dont sound good.

Well I'm glad you posted when you did Caribbean ZJ, I'll take your word since it does make sense!

top rad connection - feed. bottom -return. think gravity. Ull push high pressure air through your tranny? Dont sound good.
Gravity has nothing to do with it.The one going in the bottom of the radiator is pressure from the trans.If you look on the line you will see the anti-drainback valve I refered to in my earlier post.It goes in the bottom of the radiator.Thats what greenbronco is talking about when he said it only flows one way.

Caribbean ZJ-- what's wrong with pushing some air through? You have a pump in that trans that pushes 300 lbs in the reverse servo, a few pounds of air wont hurt a thing. Also, trans line and cooler flushes use a can of compressed propellant (air) to force the cleaner through. I didnt tell him to try to blow it up like a balloon and see if it floats, just put some air to it and see if it blows out the other end.

then again what do i know......