I have a 78 F250 quad cab with a 400 engine with no heat and its getting cold up here in NY! Truck runs cool in summer, no overheating problems, I replaced the 180 degree thermostat with a 195 degree one in hopes it would heat things up, I have an aftermarket gauge set up for temp, it gets up to operating temp now better with the 195 thermostat, stays around 190 when running. I changed heater hoses (elimated the flapper control for now-truck has/had AC), I've checked everything under dash to be ok-moving cables and switches. I put a new modine radiator in this summer as well.I even replaced the radiator cap. I've been told a plugged heater core, but neither of the heater hoses get hot, not even luke warm, I even placed a giant piece of cardboard in front of radiator, no difference.Upper radiator hose does get very hot now, so I know there is circulation. I'd go with the plugged heater core idea, but shouldn't one hose be warm and other cold if this was the case? Others have said water pump not circulating, but it should have overheated then in summer or now. Anyone have any ideas? I thought I remembered reading in the past something about a brass ring or plug or special thermostat needed for these engines to work right? I purchased a Stant thermostat that was listed for my truck, radiator was replaced because I stuck a tranny line through it (not because it was that bad).Thanks for any advice.

 

If your heater core is plugged than hot water can't flow is any direction. The only way one hose would get warm is by convection and if you wait for that to happen it's going to be a long cold drive.

 

have you pulled the hoses at the heater core and checked for flow?it can get messy but seems like the next step.a flush tee in line can offer a window into the system,before it pressures up,rad. cap off and with the tee at the highest level of the system.i've also seen a blob of sillycone block the flow from inside!that was a really tricky one.shut the eng. off,it would go hide somewhere-start it up to check flow w/the hose off,good flow.put it back together,no heat.take the hose off eng. running, no flow!!had to grab it w/eng. running and pull the buggar out.yeah it was a big one.or take both hoses from the eng. off and try to flow the garden hose either way?somethings gotta give.

 

Maybe it's airbound.. try taking the top hose off and see if there was a airpocket in the lines ...

 

Thanks, I think I'll try taking hose off with engine running and checking flow, I noticed when replacing hoses that there didn't seem to be much in lines.Also the previous owner seemed to love silicone, so I will check that too, maybe a flush with garden hose (well if it isn't frozen yet).