The most common problem for this is the thermosthat.

It could be the air blend doors, but first as suggested above, check the coolant temperature. Could be the thermostat.

As a rough check, feel the hot water hose to the heater. Does it get hot? (Use care and don't burn your hand.)

Thank you so much.
I shall try that.

Urlee

being a s-10 get it flushed. this is a common problem with s-10s and s 10 blazers, 9 out of 10 times the back flush will cure the problem. we had a fleet of s-10 based trucks and suvs for company vehicles, went through this with almost every one. believe the dealer charged about 90.00 bucke for this and took about an hr.

Wow 90 bux? I agree with the Bill on the flush part. Does the temp guage on the dash getting close to 210? It needs to run inbetween 180 and 210. Does the heater get better with engine RPM? If it does it probably needs to be flushed. We get repeat customers for this service every year. Easy to do. Take a plastic bag like a grocery bag, and place it over the Distributor cap, where the spark plug wires all plug in. This does not need to get wet. Remove both heater core hoses then take a water hose and spray into the tubes that are coming out the firewall. Go back and forth a few times untill the water comes out clean. Reattach hoses, top off water in radiator, remove plastic bag and see if you have heat.

Good news!

I did need a new thermostat.
My repair man took my truck for a run and when he came back, he said I do need a thermostat and he also back flushed it with a hose and said a LOT of crud came out so I am all set now.
Ooooof! The HOT! Have to roll down the windows now "lol"

Thank you all for your great suggestions and responses.

What engine do you have in the S10, 4.3? Go to http://www.imcool.com/
and read up on some crud issues with 1996 and on GM vehhicles.

Hi dennyin,
I have a Vortec 4.3 Liter.

Thank you for the url. I shall have to look at it.
Yes I have to use DexCool. Didn't see where to go to read on the crud?

Urlee

I don't think you HAVE to use dexcool. You can flush the dexcool and use the standard green stuff, or the universal yellow stuff if you want. Since you seemed to have already reinstalled dexcool, I'd leave it now and switch at next flush, say two years or so. It appears that dexcool turns to cr*p if air gets introduced into the cooling system. I've read enough complaints about cooling system problems related to this stuff to not want it myself.

Thank you so much gary for your input.

I shall look into this faithfully.

Urlee

It could be many things... But generally speaking, especially with the S-10 and the higher location of the heater core, it is usually caused by a terrible choice of coolant by GM, Dexcool. Dexcool tends to solidify when exposed to air. If you get air in the system, from letting the coolant level in the overflow can get too low, it will draw air back into the radiator and block. Usually the heater core is the first sign. It will plug up with solid Dexcool debris, and the heater quits suppling heat. Backflushing it will get rid of the sediment build-up, but it will likely return. You need to purge all air from the system, and then keep the level in the overflow can high to prevent air from being drawn back in. If the level continually gets low, you need to find out where the coolant is going to, look for leaks. The intake gaskets on the 4.3 are another weak point, they will start to leak coolant internally. They can begin to fail as early as 70K miles. I had the intake gaskets replaced on my s-10 at around 90K. I then switched to Napa extended life coolant, all type compatible. No more sold debris are seen in the overflow or radiator. Search for problems with Dexcool on the web, you will find it is a common problem, enough so that there have been class action lawsuits filed by both consumers, and even GM against the contractors that made Dexcool for GM.