I'm working on 1 98 Blazer. It overheats on very hot days, otherwise fine.

What temperature differential should I expect between the top and bottom hose. I am finding very little difference with a digital IR thermometer. I can see flow through the top few bars of the radiator when I run the engine with the cap off. The thermostat was opening and closing controlling flow.

I am currently running a radiator flush and have pulled the thermostat. The top and bottom hose are no more than 10 degrees different, sometime less. The engine is running at about 210 and the top and bottom hose are bracketing 178 degrees. [Note: to get the temp this high I had to turn on the A/C with the windows down to get the load on the engine].

Thanks for any info on normal heat loss across the radiator and any other measurement points.

Kevin

 

When the vehicle is at idle in park, there is no air flow through the radiator and the temperature will be almost equal at the inlet and outlet. The radiator relies on the fan clutch to pull air through the radiator. If the fan clutch doesn't pull enough air through, the engine will overheat, even with the thermostat removed. It will also cause poor A/C performance at idle as well. The thermostat regulates the coolant temperature and the fan clutch regulates the radiator and AC condenser temperature. This link explains how the clutch works and how to test it: Learn about how the fan clutch works from howstuffinmycarworks If it needs replacement, install a "Severe duty" clutch. Hayden #215158 is around $60 They are noisy, but they work!

The cooling system passages in the engine, radiator, hoses and heater core all must be clean, not just the coolant. If they are restricted with scale, rust, sludge etc, both coolant flow and heat transfer from the engine to the coolant decreases, and engine operating temperature increases.

Normal operating temperature should be ~195F to 200F. You can easily check it with a scan tool, no need for an IR thermometer.

 

The fan on my blazer runs all the time the engine is on. I thought all the radiator fans in these early 2nd gen units were direct drive.

That said I can turn the fan by hand, it does not bind, nor does it spin freely, or wobble. I do not see any signs of leakage. It seems Okay unless I am missing something.

Ps. I was using the ir thermometer to see if there were any cold/hot spots in the hoses, radiator.

 

The clutch engages and disengages depending on different conditions & temperatures. When you first start the engine, (cold start) the clutch is engaged and you should hear the fan "roar". Even with the windows closed, it is very noticeable. Depending on how cold the clutch is, it might take 3 minutes or so to gradually disengage and quiet down. The clutch will remain disengaged until the engine begins to overheat. It will then gradually engage and the "roar" sound will return until the air flow temperature through the radiator cools down. If you start the engine cold and bring it to operating temperature, and can't notice any change in the sound of the fan during that time, the clutch needs replacement.

 

I just replaced mine with a severe duty the other day. Captain is right if you can't hear it after it gets hot or on first start up then your fan clutch is bad.

 

I can't hear mine on startup, I have one on order. Thanks Captain.

 

replaced the fan clutch today. I can hear the clutch engaged when starting the engine cold and when the engine get up to highest temp. The old clutch was firm when turning it at first but quickly moved to free wheeling when turned by hand. You couldn't feel it on the vehicle, but I could on the bench.

 

Did replacing the clutch cure the problem?

 

Have not had the very hot days to find out yet. I could not get it to overheat with inlet fan partially blocked, A/C on and RPMs elevated. So I think so, but have no way to prove it.