Jim Grant's Tech Tips 03

'94 Hyundai Excel transmission leak

Q: I have a '94 Hyundai Excel and I just found out that it has a transmission leak.I was told to get some transmission "stop leak" to see if it would work.Do I need to drain all the transmission fluid out first and then fill completely with the stop leak or only drain half and fill the other half with stop leak? And how do I drain the transmission fluid? Any help will be GREATLY appreciated!

A: Brandi, there is some advice you take with a grain of salt. There is some you take and run, as far away from that advice as possible. Whatever you do "do not" put any such additive in your vehicle's automatic transmission!!!! I cannot think of any quicker way to cost yourself money than to do such a thing! It may be easier to understand if you know the basic theory of those types of additives. The thought is that a transmission oil leak is due to a hardened oil seal. The rubber sealing surface of oil seals do harden and shrink with time. When this occurs the seal will lose the ability to conform and allow for movement of the sealing area, resulting in an oil leak. These magic additives are designed to soften and swell the oil seal. Here's where this concept falls on its face. If only one seal is leaking what happens to the many other in the transmission that are not leaking when the additive is used? The internal oil seals of an automatic transmission have no room to swell and, by design, are not allowed to move/flex like the external oil seals. In an automatic transmission what might be good for one seal design isn't always good for the other. I suggest having your oil leak diagnosed first. The repair may be as simple as a new oil pan gasket or axle seal. Pouring the magic in may make more come out of your checking account.

(Jim Grant is an ASE Master Technician with advanced L/1 certification. He works as manager and technician in his family's automotive business in New Hampshire. He writes weekly automotive consumer columns and is editor of an automotive newsletter that is circulated throughout North America.)