Synthetic ATF

[4cfSVX]

The 92 LSL I bought last week had its tranny rebuilt in March. It has the OEM external filter. I am planning to replace the external filter with a Perma-cool so I can easily add temp gauge. Should I replace the ATF with Mobil 1 synthetic or similiar? A mechanic told me that if I did the seals could leak.

[4cfSVX]

Should have done a search first. Plenty of info from previous posts. Please excule this newbie. I'll be sure to check first before I post.

[lee]

edit: you posted a retraction while I was typing....

IF (and note the IF) it was rebuilt in March, and normal mileage has been put on since, changing to synthetic won't cause any seal leaks. As an FYI here's how seal leaks with synthetic ATF/oil occur.

An engine/transmission builds up a layer of (warning highly technical term to follow) "gunk" at the seal boundary. As the seal ages it wears and/or hardens. The introduction of a synthetic fluid (nominally PAO, a Type IV base stock) cleans off the "gunk", this allowing the fluid to leak by the seal.

To avoid this you have to clean and condition the seals before switching. Again, if you're sure it was rebuilt in March, you can ignore the conditioning recommendation.

For people who absolutely refuse to condition before changing to a synthetic I only recommend Redline, as it uses a higher percentage of ester/type V base stocks than the conventional PAO/Type IV used by Mobil 1, Amsoil, etc. That results in a somewhat slower cleaning process and esters have some seal swelling properties as well.

Try looking at these sites for oil and ATF conditioning (I work for Uncle Sam so I have no vested interest - you may find other good products):
www.auto-rx.com and www.auto-rx.net

[4cfSVX]

Thanks leee, for the great info. Even an often repeated question can result in new info. I am going to check those sites out now.

[LarryIII]

Whether or not your seals leak from synth. ATF, depends on the extent of the rebuild and which seals were replaced.

The '92 that I bought had 86,ooo miles on it when I git it. I changed the ATF to Mobil 1 many times. and had a drip for about 14 mos. It's finally stopped. (See one of my previous posts on Synth. ATF.)

Good Luck.

[Paisan]

Nice post. Right at the right time too. I'm planning on doing redline synthetic ATF in my 3 cars soon so that's good info.

-mike