k5 bad heater

[65truckowner]

My sons k5 blazer heater is not working as it should. It has a new heater core and the engine warmed up is just under 210. The heater hoses are hot enough that you cant hold them for more than a couple of seconds. One thing is the hose coming from the intake is smaller than the return hose for some reason. The intake hose has a crimped fitting that threads into the intake so I cant just swap them. I put a nut inside the larger hose and clamped it to see if it made a difference but it did not seem to help. Any ideas.

[65truckowner]

Well can someone tell me this, where does the return hose need to go. Now it is going to the radiator, should it not be going to the water pump?

[rpmerf]

On my 70 C20 350, one hose goes to the water pump, the other to the intake. Might had changed over the years. Mine has a 3/4" hose from the water pump and 5/8" hose to the intake.

You should be able to cut the crimp and replace it with a hose clamp.

Since both hoses are hot, I wonder if it is a HVAC door issue? Had an issue in my truck where the linkage and rod would move, but the door wouldn't.

[CSHADES]

are both hoses really hot or is one cooler than the other? The hose size really doesn't matter, the old ones were both 5/8 hose. The return can go to either the rad or water pump doesn't matter. I am thinking you have a blend or mode door issue, either something is broken or wedged.

[stanski]

Likely a door issue within the heater box .One other thing possible is an air lock at the heater core, not near my truck right now, but is the heater core above or below the top of the engine. If above, may be air locked. You could try draining the system then refill through the thermostat hole in the intake till full, then replace thermostat and start it and slowly fill the remainder of the system through the rad.

[Dead Parrot]

On my 75 C10 with AC, one hose from intake, return hose to radiator. Hoses are different sizes. 5/8 & 3/4 IIRC. Drain a bit of coolant from the system and you should be able to see if you have good flow through the heater core.

If you have good flow, likely that either your AC/Heat blend door is partially open(common reason broken white plastic piece inside the passenger area vent box) or you have bunch of trash blocking air flow through the core(mice have been known to build nests in there).

[CSHADES]

what I was referring to on the temps of the hoses is that the return hose should be about 20 degrees cooler than the supply hose if the core is shedding heat the way it is supposed too.

[Honest Bob]

In both of mine I had to remove the mouse nest that was inside the heater box.

It made a huge difference in my 77, its putting out alot of heat but the door and windows seals are mostly gone so its still not all that warm on the highway.

[65truckowner]

Both hoses seem to be the same temp. I can see the blend door cable and arm move and can hear the door bump when he turns it to the cold position. I will check to see if it opens all the way when he moves it to hot

[sweetk30]

as said before but not asked much .

were is your 2 hoses now ?

1 should be off intake and he is 5/8" and the return is 3/4" to the water pump top port or the rad tank nipple pass side .

if 1 is in the wrong spot it might not be flowing coolant .

other than this there is not much in these boxes . there stupid easy to play with unlike the newer vehicle crap .

[65truckowner]

I mentioned that in the first post. The 5/8 is coming from the back of the intake and the 3/4 is going to the radiator

[sweetk30]

sorry must have missed it .

a flowing heater core not plugged should have a 10-15 * temp drop at most . any more and its plugged or restricted .

i love my infared temp gun to help diagnose tons of problems .

[65truckowner]

Thanks for the input. I will check that and see if there is a difference. I may ask for one of the temp guns for Christmas

[sweetk30]

Originally Posted by 65truckowner

Thanks for the input. I will check that and see if there is a difference. I may ask for one of the temp guns for Christmas

good quality units are under 50 bucks . i have used them on finding a bad motor was just half the crab was plugged up . split plenum intake cold start watch each exhaust port ( bbc ) warm up . driver side was hot/cold/cold/hot and pass side was cold/hot/hot/cold . swapped a good carb on and solved his problems.

had a efi 3.0 toyota v6 with a dead skip on it . guy installed all new tune up stuff . still there . cold start test again found cyl #1 cold . started to wiggle around stuff and the injector wire popped off it wasnt clipped on . clipped it on and smoothed right out and run perfectly .

brakes hanging up . temp the calipers and rotor . the hotter one tends to be the bad position .

list goes on / on / on with uses .