Well my wife's money pit was apparently not filled in by the replacement of the leaking intake manifold. I have noticed a little antifreeze puddle by the transmission on the passenger side the last few days. Tonite with the AC blowing all of a sudden smoke started coming out of the vents. I shut down the AC but after a while a little smoke would continue to come out thru the defroster vents. You could smell the antifreeze but the car was not overheating. So now the puddle under the car is a little bigger tonite but inside the passenger area carpet is dry. I would have expected a heater core problem with the smoke but floor is dry. Don't see any obvious leaks under the hood either.

Ideas?

 

There's a 99% chance it's the heater core. The puddle you're seeing under the truck is from the leaking coolant draining out of the A/C condensate hose.

The other 1% chance is that it's one of the heater hose connections to the heater core. A leak in this area could cause coolant to run down the heater core tube and inside the cab.

 

I am going to have agree with Alloro on this one. I think he 100% right on the money.

 

Yep, Alloro nailed it unfortunately. Heater core = $1000 or 1 very frustrating weekend for me.

 

I have the same problem with a 78 F100 I just bought. Whenever I drive it for a little while it will leak antifreeze from the hose underneath the heater on the passenger side. Smoking from the vents doesn't happen often but I did notice this the other day.

Is the only solution to buy a new heater core?

 

You may try some Stop Leak or something like that first. I've heard occasionally that will work depending on how big the hole is. Mine didn't leak until it heated and the metal expanded. Best of luck.

 

I'm just back in the house from replacing my heater core. (98 expy) It took a little over 6 hours. I set my laptop up in the garage and kept referring back to the YouTube video as I progressed. Watch the video and DO IT! Just google Ford Expedition heater core and it's the first hit.

The hardest part of the whole thing was getting those darn rubber hoses off the heater core. You need to be tall to reach the back. For the rest of it I just took my time and bagged up all the little screws and nuts as I went along. There is a lot of stuff to unscrew, but it's not a technically challenging job.

A couple of posts on here said to set the blend to 50/50 hot cold, well that was complete *****. You need to set it to full cold or else you cant get the core out. It doesnt really matter because you can just hook the battery back up and change the blend if you need to.

....... and I found a couple of quarters while I was rooting around in the dash!!

 

Like everyone else said in this post, it is most likely the heater core. I would try some stop leak to see if it works. It’s worth a try, its only $15.

Here is the link for Bars Leak:

Bar's Products, Inc. - Premium Automotive Chemicals

I have used this to fix a intake manifold leak on my truck about a year ago. It never leaked again and it completely fixed the problem. They make other products for cooling system leaks that may help your situation more. I say it’s worth giving it a try.

 

Stop leak? Really.....
Stop leak = stop passages. You gotta replace the heater core, why clog your radiator with that stuff? Do a very thorough cooling system flush and replace the core. When you get it done and refill it, use distilled water and antifreeze. The minerals in tap water are a big contributer to your leak.
A BIG bit of advice, cut the metal lines on the old heater core instead of trying to uncouple the PITA fittings from the hoses. I cut mine from inside with a sawzall.
I replaced mine a few months ago and I've almost fully recovered already.