1992 Dodge Caravan rear differential leakage

You weren't worried about it before they told you. How much to worry depends on how fast it's leaking. Look on the ground, about 15 inches inside the left front tire, for a red spot or puddle. One or two drips isn't exactly something to write home about, but it should be fixed eventually. A bigger puddle should be addressed as soon as possible to avoid transmission damage from slipping clutch plates and lack of lubrication to bearings and bushings.

The differential cover doesn't use a gasket, just a bead of silicone sealer. The surfaces of the transmission and the pan must be perfectly free of oil residue to get a good seal. Only the gray Mopar RTV sealer, as far as I know, will seal through oil residue. To reseal the cover, it must be removed, and the oil will come pouring out. That's the time to put new fluid in. Chrysler used to recommend replacing the fluid every 36,000 miles. If it's time, have the cover resealed at the same time. If it's not time, and the leak is very small, wait with the cover until it's ready for new fluid. Often the leak is so small, there is just some wetness around the edges of the cover. The leak can look worse than it really is. Also, the mechanic has no way of knowing how long it's been leaking or how fast. It's a good thing he did a quick visual inspection for you, and he was right to bring it to your attention, but if you aren't seeing puddles, I think it's safe to relax.

Caradiodoc

The two have nothing to do with each other. You can go to the grocery store for chips and pretzels for tonight's football game, and go back tomorrow for next week's tv dinners. You're only out the second trip. Same with the transmission service. You'll make a second trip, but the service has nothing to do with engine oil.

If you haven't noticed a problem until now, there's probably nothing to worry about. The guys at Jiffy Lube were simply doing their job by looking for potential problems. That's better than the alternative: not saying anything and letting problems catch up to you on the road.

Most full service repair shops, new car dealerships in particular, maintain a service history of your vehicle. They would have seen that they told you about the leak many visits ago, and it hasn't gotten any worse or caused a problem. Because of that knowledge, they won't bring it up again. Jiffy Lube doesn't know the vehicle's history, so they erred on the side of caution rather than complacency. Good for them.

With the low miles you drive, and the fact you haven't been seeing puddles where you park, I'd suggest forgetting about changing the fluid for now. If it will put things in perspective, ... My '88 Grand Caravan has over 217,000 miles, and the transmission fluid and filter have only been changed once. That was at around 90,000 miles, and only because a 4 dollar side cover had a small hole rusted through it. As long as the fluid was going to drain out to replace that side cover, (not the differential cover), I decided to replace the fluid and filter. Nothing has been done to the transmission since, and I use it twice per year to pull an enclosed trailer that's bigger and heavier than the entire van! This is no longer neglect; this is abuse.

There's one extremely important fact to be aware of. My transmission is the old three speed based on the really tough transmissions used in the late 1960s through the late 1980s. They're hard to damage. You're transmission is the computer-controlled four speed with overdrive. (You will see a circle around the "3" on the shift indicator on the instrument cluster). I have a '95 Grand Caravan with that transmission. The idea behind it is really neat, (too long to describe here), but it's a wimp. If I used that van to pull my trailer, the transmission would explode before I got to the end of my driveway! In fact, that van is on its third transmission, (second replacement) at 120,000 miles. GM and Ford transmissions are just as bad. A lot of youngsters today, such as my former students, think it's normal to have your transmission replaced twice in the life of the vehicle. Yeah, it is today, but that wasn't the case 20 years ago.

With your transmission, there are actually three covers. The "pan" is the one that's removed to drain the fluid and access the filter for replacement. The differential cover is on the back. The differential is actually the rear axle built into the transmission for use in front wheel drive cars. It allows the two tires to turn at different speeds when going around a corner. That cover is only removed when it's leaking, as in your case, or when one of the catastrophic events occurs. There's a large pin that's held in place by a small bolt. The small bolt can break, often from harsh shifting back and forth trying to get unstuck in a snow pile, and it allows the large pin to slide out of place and catch on the transmission case. That's what happened to the first replacement on my '95. The case actually cracked open on the road. When the differential cover is off, the mechanic should inspect that bolt and pin, but I wouldn't bother taking the cover off simply to do an inspection. The third cover is the side pan I mentioned. No need to remove that one either unless it's leaking. There's just two gears in there, nothing else.

The rear axle, (from older cars), is built into the transmission for use in front wheel drive cars and vans. That's why they call it a "transaxle". Look for the red puddle between the two front tires, closer to the left one.

As for the radiator, the transmission cooler is built into it. There is a tube going through it that has two hoses going to the transmission. There really isn't that much fluid in the tube, and it shouldn't have lost enough to cause a problem.

Hope that helps.

Caradiodoc