Bad Thermostat?

[nwjones18]

My aunt has a 98 S10 Blazer with the 4.3 V6. The heat is not working on it and the bottom radiator hose is not getting warm while the top one is hot. The radiator was replaced last summer and I put an air hose to the heater core and it's not stopped up. Would a stuck thermostat cause this? I pulled the hoses off to the heater core and there is barely any water getting to it at all.

 

[wrcsixeight]

If the upper hose is hot, the T stat is opening.

Sounds more like the water pump is not pumping

 

[Jim_Beverlin]

What is the temperature guage reading? If the gauge is working properly it should read around 200F. At least that is what my 97 did. I would be concerned about overheating if the pump is not working. Another option is if you have or have access to an OBDII scanner that may provide the coolant temperature and give you an accurate readout. The 2 scanners I had did have coolant temperature readouts.

 

[nwjones18]

The temperature is reading about normal, when I squeeze the lower hose I can see the water level rise and feel the pressure in the upper hose, so I have to believe the radiator isn't stopped up. Can a water pump quit working as efficiently as it should? There is no noise or leaking and the truck hasn't been overheating. I am a ford guy and know the lower hose always gets hot first, but have heard that on some vehicles the upper hose gets hot then the thermostat opens for the bottom hose, but I don't know if that's right or not.

 

[crazyoildude]

heater control valve

 

[Chris142]

Originally Posted By: crazyoildude
heater control valve


Isn't one on this truck. hot coolant is circulating through the heater core anytime the engine is running.


Originally Posted By: nwjones18
Can a water pump quit working as efficiently as it should?
Yes. I've seen impellers that fell off the shaft and others that were worn out but the engine never got hot.

Are both heater hoses hot?

If they are both hot then the hot coolant is getting to the heater and you have a blend door or control issue.

If one is hot and the other cold.........Plugged heater.

Neither hot......WP ain't pumping like it should.

 

[nwjones18]

Well I'm changing my tune.. The heater core is stopped up. It has good pressure going into the core and water just barely flows out. If you run the engine up to around 3k rpm you'll start getting hot air. I guess it has enough pressure to force it through the core then. I am going to try blowing some air through it, but I'm thinking I'll have to change it. Not fun on a Chevrolet.

 

[Jimmy9190]

Is it possible to disconnect the heater hoses under the hood at the water pump and thermostat and use a water hose to back-flush the heater core to flush the gunk out of it?

 

[Rooy]

Yes, use a hose to flush it in both directions. Water pressure will work much better than air to remove gunk. To get it really clean, you'll have to use a chemical flush.

 

[dwendt44]

Flush in both directions until the water comes out clean, then do it some more.
That may be just a stop-gap fix, but it should help a bunch. Been there done that.

 

[nwjones18]

Well I flushed it both directions with water and air. Then filled it up with radiator flush and did it again. I've got heat! hopefully it stays that way.

 

[Chris142]

It will plug up again. The block is contaminated and needs to be flushed and then have the drain plugs removed and flushed with those out. Removing the lower radiator hose won't drain the block.

 

[dwendt44]

Some times, even with repeated flushes, the heater will only put out heat around town. Out on the highway, the coolant flow through the heater core is either to fast due to restrictions or to slow because the thermostat is wide open (radiator problem).

In that case, you got problems. A new heater core or a professional radiator cleaning is in order.
If there is a heat valve in the heater line, that also could be bad.
I've had both situations on older vehicles.

 

[nwjones18]

Originally Posted By: Chris142
It will plug up again. The block is contaminated and needs to be flushed and then have the drain plugs removed and flushed with those out. Removing the lower radiator hose won't drain the block.


I flushed out the system over the summer before I replaced the radiator, I'm assuming it broke everything loose and then it got caught in the heater core. We just didn't notice since we had no cause to use the heat. Hopefully that was the last of the crud and it will keep working.