Another update :

I got fed up with taking that dash all apart too and put it back together again - tired of having it look like a bomb went off inside my truck
and of course ended up with extra screws LOL
Somebody had been in that dash before too, because there were several wires that had been terminated that went no where, one was a small led light on the upper left side of the dash above and to the right of the light switch. Is there supposed to be a seatbelt chime on this truck ? Maybe that is what they unhooked ...

And in putting it back together (I have a 97 with automatic) I found that taking apart a lot of that dash stuff really did not seem necessary to get at the heater core - granted, I didn't take the whole dash off, just got it to flip forward and up a bit, enough to get my hand in there to mess with the core.

The other news tho, is that I got to the point where I was thinking it was the water pump, but before I tried that whole mess on top of this one, I wanted the dash back together. So after doing the dash, I pulled the heater core hose off the passenger side where it has a split section on the valve cover. Plugging my handy garden hose connector again ($2 from Fred Meyer - watch you dont push them too far in or you have to cut it off - ask me how I know LOL) I plugged a short section of washer/dryer hose onto the heater core hose, opened the radiator cap and stuck the end of the hose in there, then turned on the truck. And out came coolant, pumping just like nothing was wrong with the water pump.

So here is where I am now : if a garden hose is plugged into the passenger side heater hose it pumps out the driver's side heater core hose no problem. But, if just the water pump is pumping, even tho the coolant comes gushing out what appears to be pretty normally, I don't seem to get anything thru the heater core. Which would say the heater core is bad (or the water pump is bad) but then why oh why does the garden hose flush work so well ? And why does the water pump seem to pump just fine by itself ?

Anyways the truck is back together now, altho it seems my abs is not working. I'm not sure how much more time I'm going to put into this. I'm not swapping things without being able to nail down the problem and I don't see what more to try - maybe a clear hose thru both side of the heater core - but then I think I give up. One good thing, I spent some time fixing my battery terminals, replacing a bad bolt so at least that part went right.

 

Koch,

I have replaced my water pump, thermostat (several times), hoses, water inlet, completely flushed the system including flushing the radiator, used the funnel to fill while reving the engine, installed the prestone flush kit, changed the radiator cap, and still in the same boat as you are. The only thing I haven't done is replaced the heater core. The only thing I can think of with the heater core is that maybe (and that is a big maybe) that there is scale built up in the core and I am not getting good heat exchange between the coolant and the core kind of like insulation. That seems a bit of a reach. I really think it is an issue of flow through the heater core.

 

Sorry this took so long......

I finally got a bottle of CLR, totally blew out all the water inside the heater core, and filled it back with the CLR. Before I did the CLR treatment I flushed it out with a water hose, and volume as well as color looked good. After letting the CLR sit for 15-20 minutes I hooked the water hose to it again, and thats when the color started changing making me realize there was scale in the heater core. It really does make a difference.

 

I am having same problem with my 98 1500 5.9. Here are a few questions I have.

I just this last week put in a new water pump, thermostat (195*), and all new hoses. Prior to doing this I was having the inadequate heat issue and was hoping the new water pump would fix it but it didn't. The temp gauge never gets above about 170* with the new water pump, which I think is odd. Any reason why that would be happening?

What is the water circulation route? Does water come out of the block by the thermostat housing and then thru the heater core and back to the water pump via the return line on the drivers side? So if you want to backflush the heater core you need to push the water "in" from the drivers side hose and let it come out on the passenger side hose? And can you blow distilled water or CLR like the previous guy used by using your mouth? Is that enough pressure?

 

I flushed it both ways a couple of times a week before I used the CLR. I am sure you probably could blow out most with your mouth if you can reach it, but I had an air compressor. You should be alright just getting out what you can and then pouring in the CLR. I used the funnel propped up on the air tube on the pass. side, and the other hose proped against the master cylinder. That little bottle of CLR was just the right amount to fill the core and the lines.

 

Hey guys I noticed on my truck that the radiator hose was getting very hard. A month ago I had replaced the Radiator and the cap. And what I did not know until I read in the factory service manual that you can't use just any radiator cap on our trucks. I had a cap boxed by Federated auto parts ( T16) that has a spring loaded relief, not what we need. So a buddy of mine that manages a parts store gave me a Stant #10231 , that does not have a spring loaded relief. It was not letting pressure into overflow tank and pressure locking my system (no flow) . Now my hose is not getting hard (upper hose) and I now have great heat. This might be something for you guys to check into. It might just be your Radiator Cap. It's only a $8 experiament. On the Stant Cap if you hold it by the lid with the lid on the upper side you can see the relief move freely and with the regular T16 it is tight.

 

Hold cap at eye level, upside down. If any light can
be seen between vent valve and rubber gasket,
replace cap. Do not use a replacement cap that
has a spring to hold vent shut. A replacement cap
must be the type designed for a coolant reserve/overflow
system with a completely sealed diaphragm
spring and a rubber gasket. This gasket is used to
seal to radiator filler neck top surface. Use of proper
cap will allow coolant return to radiator.
This is out of manual
Clap

 

NO spring loaded cap eh?! I'm going to replace mine tomorrow!

My truck never reaches 95 celsius ( straight up and down on the gauge )

My truck blows hot air though... not SUPER hot, but hot enough to defrost a windshield.

 

This is all helpful to me also. My heater is not blowing very hot. Of course it has been 36 degrees below zero for the past few days. But that is not the problem. I think I will try to flush things when it warms up to zero or so.

 

That's -36F by the way, not celcius.