2002 Isuzu Rodeo 2.2L automatic. Temperature gauge goes to HOT after driving less than a mile. Replaced thermostat, water pump, timimg belt, coolant temp sensor, and radiator. Had system pressure tested, mechanic says engine is not blown. Still overheating, What else could it be.

the dash gauge or its sender is bad.
use and IR gun for $15 and see that the coolant is
at 180F and the old crapppy gages is fibbing,
common this.
above poster forgets to read the COLD word.
and fails you big time.

I will now read the book for you.
the SM, service manual to see how yours works
most cars changed radically from 1996 to 2000
2.2L
3.2L engine? oops both are same, had to look both.
the sensor has one wire
and is not the ECT sender with 2 wires.

My rodeo had a leak under the air intake plentium theres a medal pipe runs threw there the O rings was dried out and started leaking

You did not mention the thermostat, which is the second thing to check after making sure the cooling system is full of liquid.

check your coolant level. Check to make sure your cooling fan is running, Thermostat could be an issue also. Also check water pump. To check thermostat feel top radiator hose when vehicle heats up if it gets hot your thermostat is probably working if it does not then ur thermostat is probably stuck closed and needs to be changed. If your water pump is leaking out the weep hole (small hole at neck of water pump) then you will need to change the pump because it is going or has gone out.

BS. Water pump should be replaced with the TIMING BELT. The serpentine belt doesnt even touch the water pump. If you have a V6 that is. but you didnt say what engine you have.

the fan is not operating properly
if it is a viscous fan hub( fan clutch ) replace it
if electric fans check the relay/s and coolany temperature sensor for correct operation
chweck all wires for continuity and connection faults

There may be an obstruction in one of the hoses, there may be an air pocket in the system somewhere.
Are you sure there is actually an overheating going on? Maybe it's a bad temperature sensor or temperature gauge stepper motor.

head gasket does the overflow bootle have bubbles in it when idleing warm if does most likey rear head gasket.

It could be engine overheating, once you are turning the defroster on you are acutally turning on the compressor which is usually used for AC. If the engine has a drain it will over heat a bit which sounds like what you are experiencing. Check to make sure your thermostat is not sticking and staying closed causing the temperature change. Did they change the thermostat when they did the water pump? If they didn't I would suggest you do that sooner than later since you have 123K miles on the car. Most likely this will fix your problem.

It may actually be a coolant temp sensor problem - they do have issues sometimes. I'd replace that before anything else - they're generally inexpensive (in the $20 or less range). If, when you ask for a new one, they ask you which one you want, you need the one for the dash gauge. Some cars have one for the gauge and one for the car's ECU. Your problem is with the one that drives the gauge, so get that one.