Im having a random overheating issue with my 96 blazer 4.3 I have owned the truck since 2006 and coolant temp was always under 210 until a month or so ago. I noticed the temp rising to 220 or so at random times, coolant level was ok. Started happening more often and about 2 weeks ago went all the way up to 250 and turn the check gauges light on. Drove home cooled it down pulled the t-stat and it was gummed up and i tested it in hot water and it did not open, replaced it refilled coolant and drove it the next day, still going over 210, next i tested the rad cap and it was junk, bought a new safety cap and drove it again, still the same. Drove it home cooled it down removed the upper rad hose from the rad and flushed the radiator and block with the water hose with the engine running until clear water found. Backflushed it and reinstalled the hose refilled coolant and retested. Same result. I already knew i had bad intake gasket so i pulled and replaced upper and lower intake gaskets checked coolant passages in the heads and all looks good. I have replaced the water pump also within the last 6 months due to a leak from it. Upper and lower rad hoses and heater hoses are about 2 years old. Reassembled everything and also replaced plugs, wires, dist cap and rotor, removed and cleaned throttle body and cleaned egr valve and ports. Filled and bleed cooling system and retested same result. Reinspected clutch fan and bleed cooling system again with the right front of the truck jacked up rad cap off and heater on. Got some air bubbles out and saw good flow from what parts of the rad i could see. Retested next day same result. Rechecked fan clutch and got it to free spin, removed upper rad shroud, removed front grille and cleaned all debris from front of condensor, between rad and condensor and cleaned from engine side of rad toward front of truck to remove debris, all looks ok. Replaced fan clutch and noticed big improvement of fan noise and airflow, old clutch was deff. bad. Reinstalled everything and retested, same result. Now not sure what to due, gonna have to check rad with infared thermo. but i know head gaskets ok, i do have coolant flow, fan working good, good flow through condensor, and it runs cool for about 10 to 12 miles and then it will go over 210, so it takes a little while to act up. I have replaced the heater core about a year ago so that should not be clogged up. But i do have the random heater core gurglle noise. So maybe air still in system. Any ideas that i may have missed. Thanks

 

Sounds like there is still air in the system.

Also, just a tip, please try to use paragraphs to break up your post. One big paragraph makes it difficult to read.

 

If you can find someone with an infrared imager it would be easier to check the radiator that an infrared thermometer. It sounds like your radiator may be plugged. I bought my 97 Blazer for a grand due to over heating issues. Same as yours. The guy had the original cap, leaking heater, leaking intake ect ect ect . The dexcool reacts with air and forms jello. jello doesnt flow well through the core of a radiator.

Good luck!

 

Thanks for the replies, sorry for the long post just wanted to include as much info as possible. Thinking about pulling rad and try to flush with water hose to see if i can see anything inside of it, i know i tried it with it in the truck but wondering if being able to move it around might help. Also this have been converted to green coolant before i got it.

Any more ideas on trying to bleed it out, it think there might still be some air cause i have heard the noise under the dash this morning. Just not sure that this is the main culprit right now. Thanks Again

 

try a nice drive with the stat off and see if it acts up.

 

haha makes me wanna not read it at all BUT i did

 

Driving with the stat out wont help. it will agravate the problem if the radiator is plugged. The blazers run a t-stat that opens one port while its closing another when it gets hot. Whn its cold, the stat opens the port that just curculates coolant through the motor. When its hot, that port is totally blocked off. Pulling the stat will allow coolant to circ back into the motor instead of forcing it into the radiator.

If the radiator is blocked the upper hose will be VERY hard when the t-stat is open.

 

Oh ok thanks i will check the upper hose next time, Thanks again! Also gonna bring some rad flush home from work tommorow, and try and flush rad again.

 

I flushed mine by removing the radiator, kept radiator cap on, and ran water from a garden hose full blast BACKWARDS through the radiator. I used a rag to seal the garden hose in the lower radiator hose fitting. Plan on getting wet.

 

Is the new thermostat an original temperature one or is it a hotter opening one? Just a thought.