Hello I am working on a 2000 blazer. 4.3l no heat. the temp guage is at about 210 the coolant level is good in the reservior and the radiator is full. all of the functions on the dash switches appear to be working properly, when it is put to hot the air coming from the vents is only very slightly warm. the blower motor is working fine. the only thing I have noticed so far is the hoses coming from the heater core one is hot and the other is only slightly warm. One last thing the owner of the vehicle put in two doses of stop leak over a year ago. any suggestions would be greatly appreciated.

 

Follow the heater hoses to the motor & disconnect 'em. Try taking a garden hose and going back and forth between them try to push the crud out.

 

Yes, try reverse flushing the heater core. Do not directly connect the garden hose to the heater core. City water pressure usually runs from about 40 psi to well over 100 psi. This can break the heater core which normaly runs about 15-16 psi. Just hold the garden hose up to the heater hose with your hands. You may get sprayed but safer for the heater core.

 

By any chance, did you put in anything like Prestone instead of DEXCOOL? I did, and it gelled up the system. I had to back flush three time to get my heater core unplugged. I drove cross country back in 2007 in 19 degree weather before I decided to figure it out. Don't over pressuize the system...it makes for a bad project to change out the core!

 

Thanks for the suggestions, I will try to carefully flush out the heater core. I will ask the owner about the Prestone I really hope that is not the case.

 

I use the prestone 50/50 in my coolant system. The green/yellow that works on all breands and models. That stuff is pretty safe. If it was the glycol green stuff though, then I would probably flush the whole system and go with the all make and model's brand/Dexcool.

+1 on the back flush. If you can afford it use the prestone flush stuff as it works great for getting the rusty stuff out from old fluid that has gunked up.

 

I flushed the heater core today, all is well now thanks for all the suggestions.

 

I'm glad it worked for you.

 

Just had my heater core flushed out the 2nd time in 2 or 3 years. I couldn't hardly stand the heat when they were done. The mechanic showed me the junk he got after each of 3 times as I was sitting there. They said they flush a lot of blazers and that he thinks the antifreeze is one of the problems. If you live in the northern climate, like I do , It might pay to just have it flushed every 2 years or so. I'm also thinking of trying a Tefba filter ! --------- 2000 Blazer 130000 miles

 

I just had this same problem. All of a sudden on Friday, no heat. 2 months or so after I changed the coolant and re-filled with dexcool. To diagnose the problem after a quick google I warmed the vehicle and sure enough the left heater hose at the fire wall was warm and the right one was cold. Disconnected the pipes at the manifold and rigged up 2 pieces of heater hose with pipe nipples and flushed the heater core one way and the other until it was flowing good both ways, used light air pressure to empty it. Then we (my mechanic, really) topped up the coolant and it's working awesome again. I hope this doesn't happen again before I change the coolant to the regular green stuff (I'm hearing horror stories about dexcool and head gaskets and stuff, should've put in the regular stuff).