when i got this truck, the heat was very good, then it just kind of tapered off to none at all, i figured that there was a squirls nest or something blocking the duct, or that a previous owner had used some of that radiator stop leak and it had plugged the heater core. pulled the access door for the duct, no blockage, pulled the core and put in a new one. the heat was strong for about an hour, then nothing. a buddy of mine noticed that the return line from the heater was cool, like the anti-freeze isn't circulating properly. the coolent that came out was horable! brown and icky looking. ok, so here's the question' do you suppose it's that the coolent is old and worn out (is that even possable?) or should i go right to swapping out the water pump? i don't want to be spending money i don't need to spend by easter egging out good part for good part trying to diagnose this issue, but with morning temps in the single digits i need to reslolve this asap.
thanks for any input
todd

heater cores are easily plugged, an old truck that has ever been run on water will have rust floating around in the system that will plug a new core immediately. Instead of taking the truck to a shop and having the system flushed, just take out a $50 bill and set fire to it, it will have the same effect. I run a strainer in series with my heater, a mcmaster.com 4391k12. I have it tie-wrapped to the fender liner with two dorman help brand 5/8 heater hose barbs. That way, if you plug it up, you just remove the strainer and flush it, instead of the heater core, which is a lot more work. You might be able to back flush your heater core, it worked for me once, but put in a strainer. I also made a strainer to go in my inlet of the radiator, using stainless screen wire also available in flat sheets from Mcmaster. You cut a circle and fold it into a funnel like they taught you to make a filter out of flat paper in high school chemistry. Don't use aluminum wire mesh, it will discintigrate and shed wires down your radiator. My radiator strainer needs cleaning yearly. The only way to get the rust out of the engine block is to pull the freeze plugs and dig it out with a screwdriver, but you really can't reach all the little crannies full of rust.