Losing fluid, but where?
 

I seem to be losing fluid out of the E40D trans in my 91 E350 diesel. The problem is, I cant find where. Awhile back I replaced the filter and pan gasket and when I did that I cleaned off all of the road grime on the bottom of the trans. It is all still clean so it is not leaking from the pan. I also checked all of the tubes going up to the radiator and there do not appear to be any leaks. All of the connections are clean and do not appear to have any leaks. Further, the ground under where I park my van has been quite clean with no recent leaks. But, I am losing fluid. Where could it be going?

The only two places it can go is to leak on the ground or leak into the radiator through the in tank cooler.

So since I cant find a leak to the ground it stands that it must be leaking into the radiator. How do I tell? Is there a test I can do on the radiator?

Also, this is making me wonder about other things. If there is a leak in the lines into the radiator, that would cause a reduction in fluid pressure for the trans, right? So is it possible that it could cause other issues such as problems shifting with overdrive?

With the radiator cold you remove the radiator cap and see if there is oil there.

The leak can be small enough that it doesn't measurably reduce the pressure. Or it could be really big, but you would know that quickly. It would overfill the radiator and empty the transmission.

Well emptying the transmission basically is what has happened. The problem is that it turns out that my heater core busted a leak as well. So what I thought was rain water in my floor board turned out to be radiator fluid. Have the heater core ordered and I will get it replaced here pretty soon, but I guess until I do that, I wouldnt be able to tell.