I have a 2004 Blazer 4x4. Last summer while towing my tent trailer up the mountains the temp got between the 3/4 mark and the red line. Last winter temps was fine. Last April I had Pepboys do a cooling flush. That did not help. On days under 100 my temp runs 1 line below 210. If I turn on the AC the temp runs a line or two past 210. If I tow my tent trailer up the mountains to the lake it gets to the 3/4 mark. On days with temp above 100 the temp runs 2 to 3 lines past 210 and the 3/4 mark with the AC on. One time in June it was 106 out and I was towing my tent trailer up the mountains and my check gauges light came on. The temp was one line before the red line on the temp gauge and the AC was off. Luckily I was less than a minute from the top of the hill and I went down hill and the temp cooled back down to 3/4 mark. Another thing I noticed is before if I was towing up a long steep hill with the AC on and it got one line before the 3/4 mark and soon as I reached the top and started down hill I could see the gauge cool down fairly quick. Now if the same thing happens it takes a lot longer to cool down while going down hill. The gauge moves really slow. Before it would take less than a minute or so to cool back now several minutes if I have a long down hill. Heater works fine at all times I checked it.

I have taken my Blazer two times to PepBoys and they say the could not find anything wrong. I changed the thermostat and put in one rated for 195. I also changed the radiator cap. PepBoys said the flow was good in the radiator and they put a dye in and did a block test and all was good. I am not loosing antifreeze its always full when I check it. One day when it was running way to warm I opened the hood and check the upper and lower radiator hoses. I ran the engine to about 2500 or so from the engine compartment so am not sure of the RPM and the lower hose did not collapse.

I got a temp gun today. I warmed the engine and checked the radiator at different locations.
All temp readings are the front of the radiator cooling fins not the metal around the radiator.

Left top 104
Left middle 108
left bottom 114

Middle top 108
middle center 102
middle bottom 98

right top 117
right middle 122
right bottom 117

lower radiator hose about 2" from hose clamp 160
Upper hose about 2" from hose clamp 176
Temp gauge was one line below 210.

I am at a loss as what to do. Radiator and water pump are expensive so I don't want to change them if they don't need it.

Thanks in advance for your help

Jim

 

My daughter has a 2001 with 200,000.0 miles and the gauge when hot is just below the line before the 210 mark, A/C on just barely over the line before 210. Towing the 4 wheeler same thing. When towing and A/C on just below 210. Also when above 90 degrees also just below 210 line. No matter what it never goes more then one line above or below the line before 210.
After all that it never goes above 210 and I had the same thought as you a while back and from what I have read it's Ok where it's at.
I had a 1995 blazer and it never went over 160*.

 

I would suggest replacing the radiator. Your temp samples tell you that it is inconsistent. I recently purchased my 2004 4x4 4 dr with 169,000 that ran hot sometimes and over 90 dgrees with a/c it got real hot. A new water pump had already been installed,but the radiator appeared to have never been flushed/drained. It had sediments that had clogged the reservoir intake hose and mud came out of the drain,which is very difficult to get access to by the way. Long story short radiator looked good and acted good most of the time but it was clogged in some spots reducing cooling capacity. I think you have the same problem.

 

My 2001 Jimmy in the summer on 85 plus days runs just below the 210 mark on the dash

With my digital readouts I'm getting 190's maybe 200's in traffic. I don't think it is too much to be concerned about at those levels. This with A/C

Now the 3/4 level (I don't know what that temp is since the gauge isn't scaled worth crud) that may be something to worry about if run at extended periods like that. 240 is uh-oh territory to my knowledge and above that should trip that light.

Another thing to check would be the physical fins on the radiator, clean them out of dirt and road grime as that on them will hamper their ability to cool the car. You also have to factor in the altitude as well as the humidity as both will affect how well the air will cool the radiator

 

Contrary to what you may read on the internet, humidity has very little affect on cooling(so long as it isn't raining). Does humidity affect cooling? Yes, but.....Probably less variation than variation in repeatability of any given test. For most applications, it can be ignored. Altitude, absolutely does has an affect.













The best location to measure the coolant is the steel tube, just above the thermostat.