59woody

Ok guys, here's what I know...No heat on a 98 Blazer. Fan works good, AC works good. Flushed the heater core...no heat. Flushed the entire cooling system...no heat. Replaced T-Stat & Radiator cap...no heat. Disconnected hoses from heater core and ran engine...no coolant running through hoses. Checked hoses for blockage..didn't see anything suspicious...

So the question...why is there no coolant flowing through the heater hoses????? What else can I check???

Thanks in advance for all your help!

old_master

What is the engine operating temperature? If there is no coolant circulation, the engine will overheat. Does it overheat? Has the water pump been replaced recently?

59woody

I checked engine operating temp..runs right up to about 200..holds it steady. No overheating issues. The water pump is original...he line from the pump to the heater core stays cool to the touch, as does the return line...but the heater core was just flushed and flowed freely.....I hope its not time to send it to auction....

blazes9395

Thats probably your problem, specifically the metal tube/line from the pump casing to the heater hose, that area, its probably clogged/restricted.

59woody

I thought it was the water pump too..put a brand new (not rebuilt) waterpump on this afternoon..good job, no problems, no leaks, engine heats right up to 200..does not overheat..

But..no heat...pulled the heater hose off from the waterpump and there was no flow out of the tube, thus no flow through the heater core.

This cant be that hard!! What am i missing???

old_master

The hose on the water pump is the heater core return line, the hose on the intake manifold is the supply. Take both hoses off of the engine and flush the heater core using the lines. Flush in both directions.

___Brandon

I'm not sure on the blazer, but I had trouble with my 93 Grand Marquis and the actuator that opens and closes the ductwork when you turn the dial on your dash to ask for heat.

My problem started out not being able to turn the heat off last spring.

At first I thought the slide control on my dash board was bad, so I went and got another from a bone yard. The replacement took it from cold to hot and back to cold but it was then stuck on cold again.

I got lucky and fixed the problem by moving the selector back and forth from hot and cold over and over again. The stuck actuator under the dash loosened up and is now working great, and hopefully will keep it up all winter.
Otherwise I'll have to pull the dash and replace the actuator.

old_master

Your 93 Grand Marquis uses a vacuum operated water valve to control coolant flow through the heater core. Your valve might be binding. The 98 Blazer does not use a water valve. On the Blazer, both hoses should be HOT when the engine is running at operating temperature.

59woody

Here's a question...what kind of pressure / volume should i see coming out of the manifold line?...right now, at idle, there is some flow, not enough pressure to blow past my finger covering the hole. At higher engine speed I can feel some pressure start to build...but, since its a 16 psi rad cap, it shouldnt be too high of pressure..but what about flow? how do you judge the right flow rate into the heater core?

old_master

The pressure and flow are both low. The radiator cap allows cooling system pressure to build from the heat generated by the engine. The water pump does not build pressure, it merely moves the coolant through the cooling system.