Transmission Fluid

BHIVICK

MEMBER
JEEP GRAND CHEROKEE LAREDO

I have a 1999 Grand Cherokee Laredo 4x4 with the 4.0L Engine and automatic transmission. There are 104k miles on it. I am currently in the process of changing the transmission fluid. The pan was dropped, and about half of the total fluid came out. The rest is still in the torque converter. The pan has been put back on and the filter was replaced. When I purchased the new fluid, I got Valvoline ATF +4 fully synthetic. It said that it replaced the old ATF +3. My question is that since the person I bought this Jeep off of had the transmission fluid changed about 50k miles ago, I'm pretty sure there was ATF +3 in it, which is non-synthetic. Even tho the ATF +4 I bought says it is compatible with the ATF +3, I have been told by a couple people not to mix the newer synthetic with the old non synthetic. Since there is still some fluid (about half) left in the torque converter, should I have the transmission flushed out to get rid of the non-sythetic, or can the synthetic be mixed in with no problems. I am going to be away from home where I will not be able to be making repairs for the next couple years, so I really cannot afford to be having any serious problems with the transmission. Please help me out

1 Reply

MONKEY4421

MEMBER
9 POSTS

If you felt that the fluid was dirty enough to change it, then I would change ALL of the fluid anyway. When you leave old tired lubricant of any kind in an engine or transmission, you add the contaminates in the old fluid to your new fluid. A full transmission flush after replacing the filter will give you the best results for prolonging the life of the piece of equipment. And as far as the mixing of synthetic and non-synthetic fluids, it is never really a good idea, simply because the properties of the two fluids are so differnet, they do not give the best of service. They will live together, they just will not have a harmonious relationship.