low heat

[Smitty31]

1986 custom deluxe 4.3 v6 WO/A. I have very low heat if its hot outside it works pretty well lol. But the colder it gets the worse it does. I have replaced thermostat, water pump all hoses and flushed the radiator 3 times and backed flushed heater core. ive probaly backed flushed the heater core a dozen times atleast. What came out of heater core was pretty nasty but then would turn clear as it ran. The truck has never been hot since ive owned it. And maintains a constant water level. So my question is this. Is there a better flush to use than Prestone i would rather not pull the core out at this time. Later im gonna add air conditioning and will change the heater core then. Just really wanting to get through this winter with it.

[VileZambonie]

Are your heater hoses hot? How do you have them plumbed?

[Smitty31]

one comes out of the intake and then into the heater core the other one comes out of heater core and into radiator.

[VileZambonie]

Are your heater hoses hot?

[Smitty31]

yes the hoses get hot.

[VileZambonie]

Then your blend door is not working correctly.

[Smitty31]

How can I test that.

[Smitty31]

So if it's the blend why doesn't the heat get hot idling. Even on a day like this in upper 70's it didn't get hot just warm.

[VileZambonie]

Make sure the door is operating correctly. Verify which hose you have going where on both ends or post a pic. If the thermostat is working correctly, the hoses are plumbed correctly and the blend door is working correctly then you need to replace the heater core.

[Smitty31]

The heater hoses are two different sizes one comes out of the intake and into the heater core it feeds the heater core. The one coming out of the heater core goes back into the radiator. The heater blend door seems to function normally. Does anyone know of a better flush than prestone.

[VileZambonie]

The lower heater core hose is going to the port near the thermostat housing on the intake correct? The upper heater core hose goes to the radiator correct? You flushed in both directions? Anything more harsh may damage the core and create a leak.

[Smitty31]

Correct that is the order of the heater hoses. I have flushed in both directions. I wait a few days and flush again and the water is pretty dirty but runs clear pretty quick. I have probaly back flushed it more than a dozen times. But have only ran the prestone through it 3 times.

[75gmck25]

If you remove the glove compartment door (5-6 bolts hold it on from the bottom), you can see the top of the heater plenum, and there is a vertical vent plenum for the defroster, held on the center with a couple screws.

Remove the vertical plenum and at the bottom you should be able to see inside and view the blend door.  Move the dash lever and make sure the door swings fully in both directions.  It may be blocked by junk in the plenum (everything off the dash falls in there), or the cable might be out of adjustment.  The cable adjuster is on top of the plenum, and you can see it move back and forth when you move the dash lever.

Bruce