Does that make sense ?

 

 

I must be misunderstanding something, because I don't see how the original configuration could have been using the whole core in the car.  Let's forget that for now though. 

 

You should now have a tube in each tank.  Both tanks should be open from top to bottom, meaning that you'd have to have drilled a hole through the blocking plate that was installed in the tank.  If you didn't open up the blocking plate, you're only using the top two inches of the core, which would explain why that's all that's getting hot.  

 

To rephrase this another way, one tube should come into the top of one tank.  The liquid running into the tank should be able to go through every one of the flat tubes that join the tank.  The liquid should be able to come out every one of those flat tubes in the other tank, and go up and out through the outlet tube.  Is that what you have now?  

 

If the above wasn't clear, I'm afraid we're going to have to resort to drawings :-)

 

Cheers,

Rusty (glad the South FL boys survived)