Hey all, been a while. My 78's heater core has got a small leak in the cab, so I have been looking where to purchase a replacement and see that there are two different dimensions for NONE A/C trucks. There is a standard 6"x6" core and a high output 7 3/4"x6" core. Does any one know how to ID what kind of core you have without pulling it all apart?

This is my daily driver right now and I can afford to not have it during my work week. So I want to get the right core the first time and swap it in a day and be done with it. I guess I could bypass the core, but it's sporadically cold and hot right now and I kinda like to have my heater.

Truck is a 1978 w/ 300 L6, dealer installed A/C with the toggle switches under the middle air registers.

 

Easy, the bigger core is for the high output heater.

 

Wow, I have never seen a "High Output" dash.....now if everthing else was labeled like that.....Thanks alot for the info!