engine running too cold?

Having problems keeping my heater blowing warm. When the truck idles, it blows hot. But when driving the heater blows luke warm. Not warm enough to keep you warm. I thought the thwrmostat was maybe stuck open, so I replaced it. But that didn't fix it. I'm temped to put card board in front of the raid. Any ideas?

Before you try and block some of the radiator from getting air, (I wouldn't do that myself) try checking to see if the shut-off valve for the heater core is all the way opened first.

If this is a second gen truck (86-93) then it should have a valve that gets opened when you turn the temperature knob on the dash to the hot (or red) side.......it should be all the way opened when it is all the way to the hot side of that dial.
Once you have it there, or better while your turning the knob, look at the linkage for the shut-off valve which is right near the gas pedal area but right above the transmission hump. It looks like this.....the mechanism is circled in red....



This is a pic of the heater core housing removed from my truck, you can see I have disconnected the heater core tube in the left of this pic......it connects to this heater core shut-off valve, so what you want to make sure of when looking at yours is that your getting the full range of motion on your linkage to insure that this shut-off valve is opening all the way and your getting enough hot coolant through the heater core.





It's really just a little "ball" valve....





Opened!





Partially opened!



And closed!



If this is not being opened by your linkage when you turn the temp. knob, then your not getting the full extent of your heat source!

Check it out, but you DON"T have to remove things as I did here....I was doing a major cleaning on one of my trucks dash when I got most of these pics.

That valve checked out ok. i took off the pully wire to see if it would open more, and it didnt. maybe the heater core is getting all clogged up.

I used to block off half the radiator with black-painted cardboard. But I later just installed a 195F (or 192F) thermostat, that helped my heater performance.

You can try doing a good flush before replacing the radiator and heater core.Now this may sound crazy but I have used the product lime away(or off brand same thing),as my flush.I drained system,refilled with distilled water and two bottles of lime away and drove around for like 15-20 minutes seriously.Return drain and the crap that came out.Next just refill with water and run for 15 min and drain again.Granted I have a new rad,htr core just flushing my block out really good and did use this in these NEW items and it will remove alot more than your regular flush products I assure you.Just have your heat on,high fan,and flush out at least two times IF you use the lime away! with clean water,let the trk idle like 15 minutes or more drain,refill and repeat then mix ur coolant to water (distilled water is better) to % of temp protection. Replacing the radiator cap is a good idea too.I use the stant vent lever version.Btw I still cover a 1/4 of my rad in winter soley to speed up my heating temps with my new rad,htr core and stuff.I am pretty tired after work so If I let something off bare with me.Hope this helps in the ideas anyway.

was a radiator repair/rebuild mechanic for 2 years of my younger days in life. flush kits/products are a waste of time and money. you may be better off replacing the heater core. these trucks are 20+ years old, there's probably a ton of build up inside it not allowing proper flow.

thanks guys. new heater core is next up on my never ending parts list

If it was mine, I'd rig up a recirculating pump of some sort JUST to the heater core, and pump through vinegar (acetic acid) or dilute phosphoric acid for an hour or two to clean out the heater core. That would be much easier than replacing the heater core, if it works. Or use one of those lime/rust cleaners as stated above for bathrooms and plumbing.

This i the proper way to go, the other ideas work, for awhile. But to do it right, replace the heater core and the radiator and change the coolent once a year.