so I finally did the whole cooling system on my 81 d150. and it runs great and stays right at 185 even in the hot El Paso summer. but my problem is I am on my fourth heater core now after having to warranty the one from autozone 3 times I returned it and got one from oreilly's. so I was wondering if I by chance had the heater hoses backwards? are the heater cores directional? does it matter which hose goes to which inlet on my heater core? cause I pulled a moron and didn't check if it was the top hose on the water pump that runs to the top inlet of the heater core. anyone out there with a d150 that could help would be much appreciated.

Heater cores are not directional so it makes no difference which hose went where.

As far as I am aware, if the hoses attatch side by side it doesnt matter, but if the hoses are top and bottom it does? i may be mistaken on that but I feel like I read that on another post someone else started.

Looking at the heater core for you application they are side-by-side and both 5/8" so it shouldnt matter.

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"if it aint broke, fix it till it is"
78 Plymouth Volare Super Six wagon
89 Volkswagen Golf GTI 16v
92 Chevrolet K1500 5.7
98 Ford Escort ZX2 zetech