New engine in 2001 Blazer (Jasper Engine with 4000 miles). When warming up, engine will heat up to 210 then drop to 2 lines below 210 and pretty much maintain that temp. Was really warm in Georgia today, but engine temp. did the same as always. So, about 10 miles from home (daily commute is 33 miles one way) I decided to try my AC for the first time since having the new engine installed. The temp jumped up to 210 and stayed there. About 1/2 mile from home, I have to go up a steep hill to get in my subdivision. The temp jumped 2 lines above 210 and stayed there until I got home. I let it sit for about 45 minutes. Got in and drove it and the temp hoovered between the 2nd and 1st line below 210, never getting up to 210, without the AC being on. I know the fluids are full, I check them often (bad radiator cap and water pump with the new engine, both were leaking so now I keep an eye on the fluid level). The oil level is great also. Where should I start?

 

Try looking at the thermostat. If your water pump and radiator cap is bad, if you can, it would be best to buy new ones.

 

How old is the fan clutch? Fan shroud in place? Radiator condition?

 

Check your thermostat, there is a disc on a spring at the bottom of it, if its stuck, missing or damaged it will not push the coolant through the radiator, the disc closes off a bypass that is open when the thermostat is closed, the bypass recirculates coolant through the block, when the stat opens and moves downward it forces the disc to close the bypass port which then forces all coolant into the upper radiator hose to be cooled, if that disc isnt there to close the bypass you will only get about 50% flow into the radiator and recirculate the hot coolant back into the block. Its worth checking even if its been replaced, because an incorrect thermostat will fit in its place just fine but cause big problems.

 

New thermostat, water pump, and radiator cap installed with new engine. Radiator is only 2 years old. New water pump and radiator cap were both bad upon initial installation and had to have new ones re-installed. Will check thermostat. Fan clutch is what I am leaning toward, has never been replaced. But, with my new parts already having to be replaced once, I am suspicious of the thermostat also. Thanks!

 

Has the engine overheated with the new thermostat? I ask because there is an optional "Fail Safe" thermostat that i use that has a little extra stroke and if the engine overheats it will lock the stat wide open permanantly to allow full coolant flow, only downside is you have to replace it once thats happened but chances are you would have the cooling system open anyway if you have an overheating problem so it not really a bad thing. Fan clutch is very possible too but rolling down the road you should have enough airflow to keep it cool, if it was the clutch you should notice a big difference while parked.
So your running hot when you add a little extra heat in front of the radiator with the AC, seems like you would only have one of 2 issues, airflow through the radiator, or coolant flow through the radiator? Have you looked down into the radiator to see if there is scale buildup on the crossover tubes? Can you verify no airflow restriction? Stock grill is intact, upper and lower fan shrouds are intact, maybe pull upper shroud and make sure there isnt something between there like a beehive (Yeah that was a fun one...)or cardboard, some people stick it there for faster warm ups in the winter and forget about it or sell the vehicle and dont tell anyone (I dont know your history with the vehicle so just guessing?)
Only other thing I can think is that its running lean which will make it run hot, any check engine light? Could try clean the mass airflow sensor, when dirty the will cause a lean condition.

 

The fan clutch doesn't need to be replaced unless it stays engaged and will not disengage...makes a constant "loud noise" when engaged, or unless it never engages. But you can tell if it never engages even if the A/C is off.

 

I do have a problem when not going down the road (even when the AC is not on, the temp goes up when I am stopped or idling and goes down when I start to go down the road again). When the AC is on, the temp. goes up to 210 and stays there until I slow way down or stop, and then it goes up. That is why I am leaning toward Clutch Fan.

 

Also, when I got the Blazer back after the new engine install, I noticed a popping sound like popcorn popping. It seems the exhaust was not attached to the engine correctly when the new engine was installe. I am hearing this sound again. Would that cause my engine to run lean leading to the overheating? I talked to the mechanic who installed the new engine and they seem to think it is the fan clutch. We will see. If it turns out to be the thremostat, it is still under warranty. I am changing the fan clutch out this weekend and giving her a try. I will post the results.

 

I do know that when it was running hotter than usual the other day, the fan was not running as fast as it used too. It was slow and looked wobbly.