Well, its officially summer again and my blazer is heating up again. I recently replaced the water pump so I am positive that is not the issue. Replaced upper and lower rad hoses. I need to flush my heater core but from what I have read the HC does not really impact overheating of the engine. I replaced the thermostat last summer thinking that was the issue but I know that is not the case. I have a feeling that my radiator might be clogged but not for sure.

Any ideas I can do to either test the radiator or unclog it? I was thinking about running some concentrate through it and letting it sit overnight.

 

Need to isolate symptoms
WHEN does it tend to overheat? If going up long hill at 70 mph, it overheats.. radiator. Reason being you have changed pump, and thrmostat. The fan isnt really needed at 70
If OTOH it only overheats in slow city traffic and not on freeway, fan clutch.
Of course there's possibility of both being less than efficient but hope that helps.
If at anytime you've seen that brown sludge of overage dexcool, like in the overflow bottle,you need a cooling system flush.
follow directions with flush and only use approved solutions. That is unless you like changing head gaskets.

 

Honestly, its sporadic with the overheating. It seems like it starts overheating on the highway but only really noticeable once I have reached the 'city' driving (ie traffic lights and slower speeds). The engine will roar for about 5 seconds when applying gas and then quiet down even though the temp is still high.

I changed the water pump out of an accident. When I was changing my timing cover, I put the pump back on and it started to spew fluid from the weep hole. I replaced the thermostat last year because I thought that it was what was causing the overheating but that did not solve anything.

Also, there was some brown sludge in the overflow before I clean it out last summer. I actually could use a flush.

Is there anyway that I can determine if the clutch is bad? I read that the fan shouldn't be able to turn by hand. If I were a betting man I would say that it should be able to move by hand.

 

The stock blazer fan is heat sensitive. It should almost free spin when the truck is cold and tightens up as it heats up. If I were a betting man I'd put my money on the radiator. The lower passages get clogged before the upper ones which reduces the water flow. After the truck is warmed up turn it off and feel the radiator. If it's cooler towards the bottom then it's clogged and either needs a flush or replacement.

 

Replace the thermostatic fan clutch...

Also do you hear any gurgling noises in behind the dashboard?? You may also have air in the system..

 

I second fan clutch. Both our Blazers the fan clutch is stiff to turn at any temp. The fan clutch is most likely what your hearing & it is not locking up long enough to cool.

 

I do hear gurgling when I start out in the morning. From what I can recall I dont think I have ever been successful in stopping the gurgling. About the only time it has stopped for me is when my heater isnt working and I have to flush the core.

It didnt overheat on me today since it was cooler outside and the rain helped a bit as well.

Now from what I have read in the previous posts, if it were the clutch that was going out would I then not hear the roaring? Wouldn't it just sound normal and still overheat? It seems like mine doesnt really start to 'cool' until I reach the highway and keep on at a good pace.

There have been some mornings where it will roar for a few seconds even though the engine is cold, its been a little while since I have encountered that though.

I think I am going to try and do a good flush this weekend and get as much crap out of the system that I can providing there actually is crap in there.

 

If you have air in the system anywhere you will have overheating issues. Two ways you can bleed it out. First is a vacuum pump. Second when COLD remove radiator cap. start truck & let it run with cap off until all the air is out. This might take an hour. Sometime jacking up the front end helps. Be sure & turn the heater full blast hot.