Engine gets close to overheat with ac on

[Bunger317]

Usually not
Clogged heater core/hoses will cause temp to go up and down randomly, not related to RPMs or engine load
And never above 3/4 on the gauge
Heater core is fed from thermostat housing, so if flow is restricted it will cause coolant to heat up more in the housing and that opens thermostat more so temp drops and thermostat closes a bit, then repeats, so temp goes up and down on the gauge, but randomly because hoses or core are never completely block, unless you do it on purpose, lol

Thinking this may be my issue then. Heater still works fine but it fluctuates quite a bit even in winter now. My dads 4.0 doesn't move at all same year and everything.

 

[RonD]

Heater wouldn't work fine if core is clogging up, wouldn't warm up the cab very well
After engine is warmed up turn fan to HIGH
If air coming out starts to cool down then coolant flow thru the core is partially blocked

 

[Bunger317]

What I've noticed is when is once temp gauge goes up and if give it some throttle and get the rpm's up it starts to drop. As of the higher rpm's help it flow better

 

[RonD]

Then either the Fan clutch is failing or the water pump is

When engine is cold, has sat overnight, open the hood and try to spin the fan blades
Should be hard to spin, fan clutch is cold locked
Start engine, you should HEAR the fan pulling air then after 5-10seconds it should get quiet, clutch unlocked
Shut off engine
Spin fan again, should be easy to spin

After driving and engine fully warned up, shut off engine, like when you get home
Open the hood and spin the fan blades, should be hard to spin, clutch heat locked to cool radiator

 

[Bunger317]

Maybe fan clutch then because it has a new ac delco water pump. How hard should the clutch be to spin? I can spin it about a turn when it's cold. And in the summer when it gets really hot, I can hear it kick on.

 

[sgtsandman]

Maybe fan clutch then because it has a new ac delco water pump. How hard should the clutch be to spin? I can spin it about a turn when it's cold. And in the summer when it gets really hot, I can hear it kick on.

After initial start up and the clutch has had a chance to disengage, it should be almost completely free spinning. Before then and after the engine has warmed up, it should be difficult to spin the fan but not impossible.

If I remember the quoted specs correctly from an article I ran across the other day, free spinning, 20% of the engine speed is transmitted to the fan. When the clutch is locked, 80% of the engine speed is transmitted to the fan.

 

[RonD]

After warm up, if temp gauge starts to go up when stopped or driving very slowly, but temp starts to go down when driving a faster speeds then fan clutch is bad(assuming water pump is not)

Whole point of the cooling fan is to pull air thru the radiator to cool down the coolant when vehicle is stopped or moving slowly
At speed air is forced thru the radiator so fan is not really needed

 

[Bunger317]

After warm up, if temp gauge starts to go up when stopped or driving very slowly, but temp starts to go down when driving a faster speeds then fan clutch is bad(assuming water pump is not)

Whole point of the cooling fan is to pull air thru the radiator to cool down the coolant when vehicle is stopped or moving slowly
At speed air is forced thru the radiator so fan is not really needed

here's an example. Last weekend 40° ambient I'm going up a long gradual grade temp got up just over half. Towards the top it down shifter and rpm's went up to 3500 and the temp dropped to about the 1/3rd mark after 30 seconda

 

[RonD]

Just under 1/2 is where it should be after warm up
185-195degF, 1/2 on gauge is 200degF

Where is your at after warm up?

Temp going just over 1/2 would be normal on a longer hill