Which Transmission Line is Return Line on 2000 Jeep Cherokee with 4.0L Engine  

Question:

Helpful Expert Reply:

I've done some research on some online forums, and have seen lots of contradictory information. Some say the line that enters the top of the radiator is the return, and others say the one that enters at the bottom. Everybody seems to agree that you should trace both lines to the transmission. The line that leaves at the rear of the transmission is the return line, the line that exits the transmission at the front is the supply line. You'll just have to trace them to the radiator to see which line hits the transmission where.

If all else fails, you can try the line temperature trick again, by following this procedure:

1. Start cold engine.
2. Put your transmission into Drive for no more than 10 seconds
3. Stop engine, remove keys
4. Identify oil return line by feeling both lines, the cooler of the two is the return line

If you can't immediately determine which is which, try restarting the engine and leaving transmission in drive a bit longer.

Using an infrared thermometer on the transmission lines would immediately tell you the temperature difference between the lines. I've seen the thermometers on sale at the big box hardware store for about $ 30.00.

Or, the last resort, quick and dirty method. Unhook top line at radiator. Have a helper start the engine and quickly shut it off. The hose that shoots transmission fluid all over the place is the supply line. Messy, yet effective. If you go this route, be sure to check your fluid level when the installation is done and add fluid as needed.

I've linked you to some FAQ articles about transmission cooler that I hope you'll find helpful.

expert reply by: Mike L

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