I have a 1999 Dodge 3500 Van. Last summer the front end was replaced, and I elected to replace the radiator at the same time. When I got it back from the shop, I noticed there was transmission fluid on the bottom of the radiator. The shop said it was just left over from the installation of the lines to the radiator. After 400 miles I noticed a lot more fluid, and decided the line on the passenger side going into the radiator was leaking at the fitting. So I removed it, put on teflon tape, and the leak seemed to go away. Then last week after another trip, I saw the fluid again, and so I put teflon tape on the driver's side. But I'm still getting fluid on the bottom of the radiator, inside the fan shroud, and on the front frame pieces. It actually appears the fluid is at the bottom of the fins, where they go into the plastic housing. I've checked the lines, and they don't seem to be leaking.

I'm assuming when the transmission lines go into the radiator, they just connect to a tank across the bottom, which is submerged in coolant (although I don't know this for a fact). Which means if that tank was leaking, it would just leak into the coolant, not spill out to the outside.

Am I missing something here? I'm about to get a replacement radiator from Autozone under warranty, but I don't relish the thought of changing it out in 20 degree weather!

Any advice?

The picture shows the bottom of the radiator from underneath, looking up and forward. You can just see red transmission fluid seeping through between the silver metal part and the plastic part.

 

Looks like the transmission cooler is leaking externally. Replace the radiator again. Also I don't think Teflon tape on the threads will help seal the type of fitting on the transmission line. I believe it is a flare fitting which seals on the tubing end and adapter.

 

This is correct. Those are flare fittings, and the threads play no role in sealing things up. I would suspect that one of the fittings is still leaking, and the fluid is just finding its way to the lowest point. (there is no such thing as Gravity, the earth just sucks.......)

Also, I don't think fluid is actually circulating thru the cooler when the trans is in park, so, there won't be any obvious leakage in park. Block the wheels, set the parking brake, (assuming it still works....) put the trans in neutral, and then check the fittings again.

 

Well, I took it to the shop, and they said the fitting going into the radiator was leaking, so we ordered a new radiator. THAT one had a coolant leak, so ordered another one. The shop put it in, and said I was good to go. 400 miles later the bottom of the van is all red from transmission fluid. I took it to AAMCO, they put it on a lift, cleaned it off, ran it for awhile, and said there were no leaks. Brought it home, emptied 6 or 7 cans of brake cleaner to get ALL of the red off, and wrapped various fittings and hoses with paper towels and white towels, then took a few test drives. The towels stay clean, but there is STILL fluid ending up on the outside of the radiator. At least I've narrowed it down to the left side. Can't figure out where it is coming from. I'm about to tape a bunch of towels in there and just live with it, adding trans fluid every few hundred miles, but that doesn't sound too safe. TWO shops can't find the leak. I'm out of ideas, short of ordering a FOURTH radiator....

 

Skip changing the radiator again, get an external cooler, and bypass the radiator cooler altogether. See if the problem goes away.

 

If the leak is still coming from the radiator then the shop is now obligated to stay on it until it's fixed. Perhaps it's time to replace the radiator with one from a different source. Wherever you've been getting them from could've run into a bad batch.

BTW, have you looked into the possibility the red fluid is from the power steering system?

 

Down for a week with the "C" sickness. Yesterday I went back to it, and realized the transmission cooler was actually the PS cooler. So many lines wrapped around, it was hard to tell. Took things apart and finally found the cooler. Two rubber hoses were kind of wet, so cleaned everything off, wrapped paper towels around everything, and drove it hard for a half hour. Nothing was wet when I checked. Going to replace those two hoses anyway. The only thing I can think of, is that AAMCO said one of the lines wasn't "clipped in" correctly, so maybe that one dumped enough fluid around the bottom of the radiator that it's taken awhile for all of it to blow out. Either that or the leak magically healed itself.