99 F250SD V10. There are two connections on the heater core at the firewall. Is there an 'inlet' and an 'outlet' or does it not matter? Put a cummins in the truck, the V10 has been out for a while and cant remember which one is which. Thanks.

 

If the core is like my 00 PSD, it won't matter. All the newer stuff uses internal doors in the heater box to really control how hot or cold the truck interior is. You'll find you can get MUCH more cooling if you install a shutoff in a heater line.


But FWIW, I'm pretty sure my inner most connection is the inlet and outer most is the outlet. If you have issues with the quick connect connections, you can either do away with them or buy replacements.

 

Great info, thanks.

 

"do away with them"?
is it possible to just use good ol fashioned hose clamps and be done with it??

 

Yes, it is. You cut the factory crimp rings off and remove the ends. You can just slide the heater hoses over the ends of the heater core and use regular hose clamps. I did that for a while and finally decided I wanted the flex that's built into the factory style fittings. So I took the hoses loose and stuffed the replacement fittings in the hoses and connected those back to the heater core. That's how mine's been operating for the last 50k or so.


I ran for probably 5k with just the clamps on the hoses attached directly to the core. No issues seen in that time. I just felt that the factory fittings offered a little strain relief in comparison to direct hose to core. So I put them back in. IIRC, it's a 5/8" size.

 

And to clarify my earlier statement of "you'll get much more cooling with a shutoff"; I meant the a/c is much more effective with the shut off. I can get condensation on my windows when I shut off the flow to the heater core. Otherwise the air path pushes air through the heater core while its trying to cool it with the a/c evaporator. I don't shut it entirely off, just most of the way. There are some folks who think closing it off entirely leads to premature heater core failure. Partially closing it down had no effect imho.