My 98 2dr 2wd Blazer is overheating when it idles in one spot for more than a few minutes. When I say overheat I mean it will climb to the mark inbetween the 210 and 260 degree marks. The outside temp is over 100 degrees and the AC is on. When I resume acceleration it will shift out much later and I can hear the fan roaring quite loudly so I believe it is engaging. When I am moving down the road at any speed it will be at a steady temp around 200. Does this sound like I may need a flush and if so should I do a back flush with a garden hose or a chemical flush?

Tonight I will try and spin the fan clutch cold and hot and see if it appears ok. I will try to check for debris around the radiator as well.

 

It could just need some antifreeze in it... I'd also check the thermostat, esp if it's never been changed. Check hoses etc.
Not sure if the 98's are the same, but on the 97's the fan should run all the time since its belt driven, unless something has caused it to quit.

 

Mine is belt driven but has a fan clutch. I tested it cold and it spins freely, but stops once you let go. I believe that is right. I will let it get hot later and it should have more resistance spinning by hand.

I checked the coolent level already and the thermostat was replaced with the new engine 3 years ago.

Since it only overheats sitting still it makes me think its low airflow, but the fan seems ok.

 

Turn the air off when stopped...0 cost solution. I remember when I lived in Arizona and the temp was 115 in the shade...160 in the sun without the air on. Did you put in a crate engine or a used one? Air flow is only one factor in cooling an idling car. The fan only spins as fast as the engine and since idle speed is only 500-600 rpms you don't get a lot of air through the radiator so it will run a bit hot. In an area with high ambient temperatures an electric fan is better for city driving. That assumes that there are no other issues with your car such as radiator or water path blockages.

 

I will try your suggestion of turning off the AC if I ever get caught idleing somewhere and the engine temp is taking off on me. It is a new crate engine. I think my radiator may still be somewhat obstructed from neglect of never flushing it. The coolant is 3 years old along with the new engine, the radiator is original. But if it really were obstructed I would think it would run hot all the time.

We have been having record highs of up to 110 degrees here in Oklahoma so I know that factors into it all.

 

There is nothing wrong with it! 210 - 260 in 100 degree weather with the AC running and sitting idling? Sounds perfect!

Unless it starts to boil over, or TRULY overheats. Dont touch a thing.

 

Do you drive Nascar on weekends? You're right in that with the proper coolant mix and pressure it will not boil over but the temp shouldn't go much over 210 in a properly functioning system. Since the radiator is the original It's possible that there are some clogs near the bottom of it. Feeling it after running to see if it's hot all the way down would tell a lot. Radiators tend to clog at the bottom before the top.

 

Mine is doing the samething so glad i saw your post my radiator and whole cooling system is brandnew and it has been flushed 2 different times just this year i am in nebraska and the heat is crazy hot here. Mine will cool back down if i shut off a/c

 

Not sure what kind of Coolant you are using.
Not sure what your mix is with coolant and water.
A 50/50 mix with a working 15 PSI radiator cap
should give you a boiling point close to 260-265 degrees.
I know it has been very hot in the midwest lately.
I have an older vehicle that I have changed everything
over recently. I put in a new all aluminum radiator, along
with Propylene Glycol Antifreeze & Engine Coolant. A 60/40 mix.
No DEX Cool Here anymore.
I have had the air conditioning running while idling when it has
been 100 plus outside. My truck idles around 700RPM at a standstill w/AC.
I have had a scanner on it and so far it has not gotten above 208 degrees
even at idle when it is 100 plus outside. It drops to 196 at 30mph.
I have had the changeover for about a year now.
I use synthetic fluids/oils on anything I can put into her.
I think this overall helps keep her cool too.
I believe to keep any vehicle cool at those Oklahoma temperatures for this
summer everything has to be working perfectly with each other.
Just some thoughts.

Mark

 

The fan clutch should not spin freely cold - it should give some resistance. If there's no resistance, your clutch is bad.