Re: Heater core replacement procedure '99 S10?
First off, thank you very much to all of the people who have posted their ideas and suggestions about this topic. It has saved me a lot of time and money! I just wanted to post about my experience with the "No heat" problem with 98-02 Sonomas.
I bought a '99 Sonoma earlier this year for my son. It has had 3 previous owners, so I really have no idea how well it has been maintained. About a week ago, my son complained that the heater and defroster weren't working. (We are in Boise, ID, so the nights are starting to get nippy this time of year) I got online and started going through these threads. Here is what I did to solve my problem, start to finish:
1) I checked the blend door actuator to see if it was working. I did this by opening up the glove box and releasing the springloaded catch, which allows the glove box to swing all the way down, giving me access to the area behind it. You can then see the blend door actuator sitting on the top right side of the heater box. With the key in the "On" position, turn the heat control from full cold to full hot. As you do this, shine a flashlight on the blend door actuator, specifically on the rod the actuator is connected to, which goes directly down into the heater box. Make sure this rod is actually turning. If it is not turning, chances are you have a bad blend door actuator. (You can change this actuator without removing the dash, but it is tricky. See some of the other posts here about how to do that.)
2) Going under the hood, I removed the blower motor resistor. This part is located just to the left of where the heater core water hoses go through the firewall, on top of the black plastic case (not sure what this piece is called, but you get the idea). When you remove the resistor, you can actually see the blend door. Once again, with the key in the "On" position, turn the temperature control knob to full cold. Note the position of the door. Then turn the temp control knob to full hot. If the door has moved, you know that part of the system is intact, and the blend door/actuator are working and doing their job. (If you move quick enough, you can actually see the door move. Or you can just have someone else turn the knob while you watch- that way, you don't have to put down your beer)
3)The next thing I did was take the truck down to Meineke and had the radiator fluid changed and the system flushed. I could have done this myself, but I didn't want to deal with the hassle, cleanup, disposal of old fluid, etc. Apparently, the fluid hadn't been changed since the truck was brand new. The manager said the fluid was in the top 10 dirtiest radiator fluids he had ever seen! I asked if he flushed the heater core directly, and he said he hadn't because their machine couldn't hook up directly to the heater core connections. (I think this is BS, but I haven't seen the machine, so...) Anyway, he told me to run the truck for a couple of days and see what happens. He also quoted me a flat $1000 to change the heater core, if required. That seems in line with what everyone else is saying here.
4) A few days later, still no heat. So I decided to flush the heater core directly myself. I did this by following the water hoses from the heater core to their connection points on the engine block. I disconnected them from the block, and then took a garden hose with spray nozzle attachement and sprayed first into one hose, allowing the water to flow freely out the other end, and then doing the other hose. I got quite a bit of orange junk (solidified Dexcool) out of there the first couple of times. I then did each side again, this time pulsing the spray nozzle in short bursts to get more pressure through there. On one of these pulses, a BIG batch of hardened Dexcool came out. After 6-9 times of doing this, I reconnected the hoses, refilled the coolant, and started it back up.
I decided to go for a drive to help the coolant warm up faster. During this little test drive, the temperature gauge started climbing past the normal midrange. I didn't want to be caught too far from home in case of an overheat, so I went back to the house. I stopped out front, and let the engine idle. The temp gauge continued to climb up to just short of redline. It stayed there for about 2 minutes, and then suddenly dropped right back to the normal midrange. During this whole test drive, the heat would come and go, but would never remain steady, hot or cold. I was thinking that I didn't have the problem fixed. Then, after the temp went up to redline, hung there, and then came back down, the heat started coming out full bore!
Ultimately, I think it was just a clogged heater core (which, when the junk came loose, got temporarily hung up in the thermostat, causing a near overheat). This has fixed the problem for now, but I'm sure I've got a heater core change coming in the future- hopefully a few years from now. But, armed with the knowledge from this chat board, the job will be a cakewalk.
Once again, thank you to all of the people who have posted on here. It is really cool to see regular people helping other regular people, and keeping us all from getting screwed by the dealerships!