Heat problem

[Ch89]

So the issue I'm having with my 89 k1500 5.7 the heat will only blow luke warm out of the vents and defrost it seems to blower warmer out of the floor vent I've replaced the heater core and checked the hot/cold flap and is seems to be working as it should and the t stat is not stuck open temp gauge is reading around 180 when driving it's 5 degrees out side I tried to block off the rad to get temp higher and is seems to make the heat cooler any help would be great

[CamGTP]

Can you put a temp gun on the heater core lines itself to see how hot those are getting?

[Ch89]

I do know that after the drove it the return side going to the rad was much cooler

[richard wysong]

if not feel the heater hoses, they should be about the same temp. if 1 is cooler than the other you have a restriction somewhere. they should be almost too hot to hang on to with a high idle fully warmed up. if that checks out it has to be in the heater box. did you do the core yourself ? AC? manual or electric controls?

[richard wysong]

so it has a restriction either in the heater core the hoses or the pipes off the engine. if the feed pipe comes off the manifold pull the hose and look for corrosion or any trash that may be there. if thats clear pull the return and hook up the garden hose to back flush the core. they make a tool that attaches to the g hose with an air fitting on it to give it a good blast but a regular hose with good pressure will do the trick. watch what comes out when you hit it with the water you may see a blob of sealer or other smat come out

[richard wysong]

if you get a bunch of crap out of the core you may want to forward flush it then reverse it again to get it all out then figure out why a new core clogged. I know in the late 80s they had a problem from not cleaning out the casting slag when they cast the blocks but that usually rotted the freeze plugs from the inside out

[Ch89]

I will check tonight 

 

[richard wysong]

if it still has those quick connect fittings on the engine that may be your clog . you can get new 1s or replace them with a nipple, they usually leak if you try to reuse them. careful they often snap off when you remove them. if they do the best way to get the broken piece out is to cut it almost thru with a saw blade them carefully collapse it with a chisel then chase the threads

[richard wysong]

did you have any luck finding the restriction?