S-10 blazer, no heat, challenge yourself on this one!

Thank you in advance. Here goes. Own a 2004 Blazer, last model made in the s-10 model? Anyway,I had no heat. Opened the radiator, discovered 'mud'. I drained and flushed all lines....started it and 'great success', heat again....for a little while then cold air, no heat. Hmmm....blocked heater core I think...again flush heater core (with hoses detached), in one side with the hose, flush water thru till clean water comes out other side, and reversed it just to make sure. Wallah, heat.....for a lil' while then nada, cool air again. Invested time and more money in a flush 'system', did it till, no doubt, clean water everywhere-it is as flushed as it will get!!! There can not be any clogs! Sometimes the inlet hose would be noticeably hotter than the 'return' hose so I started blazer and disconnected both hoses from the heater core to see...... There was no coolant going into the heater core, nor any coming out!!! Now what?? I assume, that sometimes there must be coolant making its way into the core, but then eventually stops. What's up?:banghead: Be advised the temp gauge remains at normal the whole time no matter what is happening, it is not stuck however, it seems to be operating normally. TY

I would assume its the thermostat.

Thank you in advance. Here goes. Own a 2004 Blazer, last model made in the s-10 model? Anyway,I had no heat. Opened the radiator, discovered 'mud'. I drained and flushed all lines....started it and 'great success', heat again....for a little while then cold air, no heat. Hmmm....blocked heater core I think...again flush heater core (with hoses detached), in one side with the hose, flush water thru till clean water comes out other side, and reversed it just to make sure. Wallah, heat.....for a lil' while then nada, cool air again. Invested time and more money in a flush 'system', did it till, no doubt, clean water everywhere-it is as flushed as it will get!!! There can not be any clogs! Sometimes the inlet hose would be noticeably hotter than the 'return' hose so I started blazer and disconnected both hoses from the heater core to see...... There was no coolant going into the heater core, nor any coming out!!! Now what?? I assume, that sometimes there must be coolant making its way into the core, but then eventually stops. What's up?:banghead: Be advised the temp gauge remains at normal the whole time no matter what is happening, it is not stuck however, it seems to be operating normally. TY

OK-Educate me, what's the therms job and how does it work, if it's 'broke' it could shut down flow to the heater core? Shouldn't there always be flow to the heater core regardless of 'outside' factors just because of the way the coolant hoses are laid out, the 'plumbing' so to speak, no?

Thank you in advance. Here goes. Own a 2004 Blazer, last model made in the s-10 model? Anyway,I had no heat. Opened the radiator, discovered 'mud'. I drained and flushed all lines....started it and 'great success', heat again....for a little while then cold air, no heat. Hmmm....blocked heater core I think...again flush heater core (with hoses detached), in one side with the hose, flush water thru till clean water comes out other side, and reversed it just to make sure. Wallah, heat.....for a lil' while then nada, cool air again. Invested time and more money in a flush 'system', did it till, no doubt, clean water everywhere-it is as flushed as it will get!!! There can not be any clogs! Sometimes the inlet hose would be noticeably hotter than the 'return' hose so I started blazer and disconnected both hoses from the heater core to see...... There was no coolant going into the heater core, nor any coming out!!! Now what?? I assume, that sometimes there must be coolant making its way into the core, but then eventually stops. What's up?:banghead: Be advised the temp gauge remains at normal the whole time no matter what is happening, it is not stuck however, it seems to be operating normally. TY

Remove heater hoses and see if you can blow air threw the heater core.
Also make sure you have coolant pressure out of the hot feed heater hose.
I have had good luck reversing the heater hoses for 3-4 days or a week to help clean out a part clogged core.

"Remove heater hoses and see if you can blow air threw the heater core."
Also make sure you have coolant pressure out of the hot feed heater hose.
I have had good luck reversing the heater hoses for 3-4 days or a week to help clean out a part clogged core.

1.....I have taken the garden hose and forced water from one side thru to the other, both ways- with water flowing generously in and out-no clogs!
2.....I do not have any pressure out of the hot feed, so what is it? Am I getting closer to an answer? Like I said earlier, I disconnected both hoses from the heater core while the car was warm and running and no coolant was coming out.
3....Please don't stop-HELLLLLPPPPPPPP!!!!!!

"Remove heater hoses and see if you can blow air threw the heater core."
Also make sure you have coolant pressure out of the hot feed heater hose.
I have had good luck reversing the heater hoses for 3-4 days or a week to help clean out a part clogged core.

1.....I have taken the garden hose and forced water from one side thru to the other, both ways- with water flowing generously in and out-no clogs!
2.....I do not have any pressure out of the hot feed, so what is it? Am I getting closer to an answer? Like I said earlier, I disconnected both hoses from the heater core while the car was warm and running and no coolant was coming out.
3....Please don't stop-HELLLLLPPPPPPPP!!!!!!


Is engine running at normal tempt?
Rad full of coolant?
Good circulation in rad?
Check heater pressure hose back to engine.

"Remove heater hoses and see if you can blow air threw the heater core."
Also make sure you have coolant pressure out of the hot feed heater hose.
I have had good luck reversing the heater hoses for 3-4 days or a week to help clean out a part clogged core.

1.....I have taken the garden hose and forced water from one side thru to the other, both ways- with water flowing generously in and out-no clogs!
2.....I do not have any pressure out of the hot feed, so what is it? Am I getting closer to an answer? Like I said earlier, I disconnected both hoses from the heater core while the car was warm and running and no coolant was coming out.
3....Please don't stop-HELLLLLPPPPPPPP!!!!!!

Check the heater hoses for being stopped up and the heater hose connections/pipe plugs to engine and intake and or water pump.
If water pump is circulating coolant it should be pushing water threw heater hose.

Replace that radiator cap! Could be the cause of mud. If your holding temp at normal on the gauge then I think there is pressure. Could also be that the water pump is not circulating as much as it should. Maybe the fins are getting worn in the water pump.

Replace the thermostat with a 192f version.

Replace the radiator cap with a version that is NOT Acdelco.

If the water pump wasn't working properly, wouldn't the temp in the car (temp gauge) be affected also? It's true, there is no pressure coming from the water pump-I too suspected the water pump, but then why is car not overheating, etc.?

Try what BlazerLT said. Replace the t-stat and the radiator cap. T-stat could be stuck open and the cap could me malfunctioning and letting air in. This would explain the muddy coolant because air contaminated the dex-cool. Also this would explain no pressure in the hoses having a open stat and defective cap. Both are really cheap. 10 dollars total could fix this. If that doesn't fix the problem, then I would look at water pump. Hope this makes sence. It did while I typed it.

I'm not really familiar with the late model S-10s but I know some vehicles have heater control valves that regulate the heated water going to the heater core. Maybe you have one of these and it is malfunctioning.

Are you sure that you're putting enough coolant in? You can't just fill the radiator and recovery bottle after you flush, you have to run it with the cap off until the thermostat lets go and the coolant level in the radiator will immediately drop. Then you top it off. Otherwise you won't have anywhere near enough coolant in the system.

You guys are a home run, and I do appreciate it (i am married, but the following is gay, I know...Its nice to see that there are strangers in this world who will another stranger, no questions asked). Thank you, I will try these latest things and will see. One more note, I go out today, pretty decent distance-no heat. Coming home, have heat for a little while........:banghead: :banghead: :banghead: :banghead: :banghead: :banghead: :banghead: :banghead: :banghead: Thanks again- i will advise of the cure when it happens.....

Replace the 195f stat and the rad cap and run the engine with cap off and top off the coolant as the stat warms up and open and sucks coolant into the engine. Keep topping it off till it start puking out and then put the cap back on quickly.

I changed the thermostat and low and behold everything works great-hot hot heat. So that was it, but I still dont get why the truck wasn't overheating with a busted stat?

I changed the thermostat and low and behold everything works great-hot hot heat. So that was it, but I still dont get why the truck wasn't overheating with a busted stat?

It will overheat if it was stuck closed.

Yours was stuck open.

Geeze, howd I miss this one.

Lt is right. When the T-stat is stuck open you are cooling the engine as much as your cooling system can (minus the fan, which probably never had a chance to turn on).

OK, I've sat and read this whole thread because I'm having a similar problem(muddy coolant, incosistent heat) in my '98 ZR2. I replaced my therm. a week ago(192F), ran the truck, topped off the coolant, everything was great for a week.

Today, inconsistant heat again.

I've got something different in my problem though. My truck IS overheating. . .Kinda. The temp will get up to around 230-240 for awhile, then go back down to normal for awhile, then back up for awhile, but it never really hits 250 and sets the "check gauges" light off. When it's at normal temp., I get great heat. When it's hot, I get no heat. I've turned the heat on and off and tried it both ways, temp. gauge still goes up and down constantly.

Any more suggestions?

OK, I've sat and read this whole thread because I'm having a similar problem(muddy coolant, incosistent heat) in my '98 ZR2. I replaced my therm. a week ago(192F), ran the truck, topped off the coolant, everything was great for a week.

Today, inconsistant heat again.

I've got something different in my problem though. My truck IS overheating. . .Kinda. The temp will get up to around 230-240 for awhile, then go back down to normal for awhile, then back up for awhile, but it never really hits 250 and sets the "check gauges" light off. When it's at normal temp., I get great heat. When it's hot, I get no heat. I've turned the heat on and off and tried it both ways, temp. gauge still goes up and down constantly.

Any more suggestions?

1.) You continue to drive it like that and the engine will be toast.
2.) Flush your cooling system including the heater core ASAP.
3.) Install a Stant rad cap.

I don't get why in gods name you have muddy coolant, yet you are not flushing the cooling system and just topping it off and driving it some more?

Comon man, common sense.

I've flushed the damn thing once already. . .I'm doing it tonight and using a chemical cleaner this time. If you'd like to offer intelligent and positive suggestions, that's great. Don't "common sense" me.

Anyway, I pulled the hoses leading to the heater core off tonight so that I could flush the whole thing out again. They were badly clogged with what appears to be crystalized radiator fluid (??) Is that even possible? I suppose it could be rust or something else, but it sure looks to be like reddish black, burnt-up radiator fluid. When I drained the radiator this time I let everything flow into a clear one-gallon container so I could look at it (last time I drained it into an oil pan). There were obivously chunks of the same solid gunk floating in the fluid.

Radiator fluid doesn't evaporate and crystalize, does it? What else could this crap floating in there be? I'm not driving it the rest of the week, so that I can screw with it this weekend.

Thanks for any mature and intelligent advice.

I've flushed the damn thing once already. . .I'm doing it tonight and using a chemical cleaner this time. If you'd like to offer intelligent and positive suggestions, that's great. Don't "common sense" me.

Anyway, I pulled the hoses leading to the heater core off tonight so that I could flush the whole thing out again. They were badly clogged with what appears to be crystalized radiator fluid (??) Is that even possible? I suppose it could be rust or something else, but it sure looks to be like reddish black, burnt-up radiator fluid. When I drained the radiator this time I let everything flow into a clear one-gallon container so I could look at it (last time I drained it into an oil pan). There were obivously chunks of the same solid gunk floating in the fluid.

Radiator fluid doesn't evaporate and crystalize, does it? What else could this crap floating in there be? I'm not driving it the rest of the week, so that I can screw with it this weekend.

Thanks for any mature and intelligent advice.

Flushing your cooling system is not just cleaning the rad, and piss off about the intelligent and mature advice bullshit, I was trying to help you.

You didn't flush it last time seeing if you did, you wouldn't have crud in your cooling system. You said you topped it off, if you flushed it, then SAY THAT and don't think we are all goign to read your mind.

Replace your rad cap ASAP, it is what is causing the cooling system to failure and allowing air into the cooling system.

You can do all the flushing you can, but it will return to crap all in short order with the stock AC Delco defective rad cap.

I've flushed the damn thing once already. . .I'm doing it tonight and using a chemical cleaner this time. If you'd like to offer intelligent and positive suggestions, that's great. Don't "common sense" me.

Anyway, I pulled the hoses leading to the heater core off tonight so that I could flush the whole thing out again. They were badly clogged with what appears to be crystalized radiator fluid (??) Is that even possible? I suppose it could be rust or something else, but it sure looks to be like reddish black, burnt-up radiator fluid. When I drained the radiator this time I let everything flow into a clear one-gallon container so I could look at it (last time I drained it into an oil pan). There were obivously chunks of the same solid gunk floating in the fluid.

Radiator fluid doesn't evaporate and crystalize, does it? What else could this crap floating in there be? I'm not driving it the rest of the week, so that I can screw with it this weekend.

Thanks for any mature and intelligent advice.


As said if you done a proper flush the coolant would be clean.

Are you sure it is actually heating up or is your gauge not reading right?

If the coolant has that much crap in it has the Dex Cool been mixed with old green coolant?

You mix yellow and green and you will get brown mud.

As said if you done a proper flush the coolant would be clean.

Are you sure it is actually heating up or is your gauge not reading right?

If the coolant has that much crap in it has the Dex Cool been mixed with old green coolant?

You mix yellow and green and you will get brown mud.

I had the same problem occuring in my truck a year or so ago, it was the rad cap not holding pressure and allowing the coolant temperature to rise and the boiling point to drop.

OK, I took off the hoses into and out of the heater core and radiator tonight. All four hoses were lined with the same rust-colored crystalized chunks. I replaced all four with new hoses.

I used a prestone "superflush" kit to chemically flush the entire system, then I flushed with just water two more times. After that third flush I finally got clear water to run out consistently, even with the motor running and such.

You wouldn't believe the amount of that crystalized crap I had in my system. I've got a gallon jug sitting in my garage that is half full of anti-freeze, and half full of what looks like rust-colored gravel. When I drained the fluid last week, I got thick muddy fluid, but no sediment. I guess it was stuck in the system somewhere.

I need to replace the therm again (it's stuck open now) and I probably need a whole new radiator (I'm thinking the chunks are rusted pieces of my radiator's guts). But the truck isn't overheating for now. I drove it around for about a half hour tonight and it never got over 195 for a second.

I'm trying to figure out what could have caused that much heavy sediment in the cooling system. The truck only has 70,000 on it, and I've never touched the cooling system until last week. I just want a gameplan for what's getting replaced this weekend.

Quote from your upper post.
The truck only has 70,000 on it, and I've never touched the cooling system until last week.

A cooling system should be serviced every 3 years or 50K.
People that do have no trouble.

Not servicing system and bad rad caps and bad pressure systems and leaks and mixing green and Dex cools are leading causes to problems like yours.
MT

I bought the truck from a chevy dealer last year with 51K on it. I would HOPE they at least changed the fluids when they got it in. Even if not, the Owner's Manual says the Dex-Cool should last 100K with no issues.

Anyway, back to my last question. Any ideas (other than mixing the wrong coolant types, I know that didn't happen) on what would have caused rust chunks or whatever they are to be floating loose it there? I just want to know so that I can

a) decided if I'm putting on a new radiator this weekend
b) keep it from happening again

Also, if I'm radiator shopping in a junkyard, any warning signs of missuse I should be looking for before buying one?

Thanks for all the help and advice.

I bought the truck from a chevy dealer last year with 51K on it. I would HOPE they at least changed the fluids when they got it in. Even if not, the Owner's Manual says the Dex-Cool should last 100K with no issues.

Anyway, back to my last question. Any ideas (other than mixing the wrong coolant types, I know that didn't happen) on what would have caused rust chunks or whatever they are to be floating loose it there? I just want to know so that I can

a) decided if I'm putting on a new radiator this weekend
b) keep it from happening again

Also, if I'm radiator shopping in a junkyard, any warning signs of missuse I should be looking for before buying one?

Thanks for all the help and advice.


Read pois no 26.

Gm streaches things a little on the 150K 7 year coolant.
Like Blazer LT has been trying to tell you even a bad rad cap will mess up things.

Junk yard is not a very good place to find a rad.
Parts places or 1 800 radiator has new rad's at a good price.

If the truck is a 98 and coolant has never been changed is a good reason for coolant to be bad.
Even GM best shot is 7 years on Dex Cool coolant.
Good luck MT

Anyway, back to my last question. Any ideas (other than mixing the wrong coolant types, I know that didn't happen) on what would have caused rust chunks or whatever they are to be floating loose it there? I just want to know so that I can

a) decided if I'm putting on a new radiator this weekend
b) keep it from happening again


If you get low on dex-cool or if too much air gets in there you can get chunks. Leaking intake manifold gaskets on these model years help this along. That's why everyone is saying to replace the cap. Very important. A bad cap will allow air to suck in.
Also, if you overheat dex-cool it will clump up. Personally, I flushed the dex-cool out about 3 years ago and replaced it with the 'safe for all colors' coolant. I haven't had any problems since. My water pump died right after the flush, but that always seems to happen to me.
I wouldn't bother with a junkyard rad.

one word........warranty? shouldnt an 04 still be under warranty? let them deal with it.