The fan should be 2 circuits, one for high and one for the other three speeds. Check the fuses, it oculd be the resistor pack(its seperate for high setting), or the switch on the dash. Usualy culprits.

Too clean the radiator just spray water through it. tO flush the radiaotr you pop of the radiator hoses and stuf your garden hose in each one and let it run for a few minutes, then switch rad hose. Stuff the garden hose in the water pump, and stuff it in the thermostat housing opening after you remove the thermostat. This flushes and back flushes the engine, radiator, and if you let it go long enough your heater core. Replcae the thermostat with a new one, replcae and hard radiator hoses, and install a new radiaotr cap.

 

Another thing you can check for overheating is your clutch fan operation.
Turn the fan by hand when the engine is cold, then turn it by hand when the engine is warm. (engine off of course)
There should be more resistance when it's warm.
I have a test that I use (not for the weak of heart), I take a piece of heater hose and see if I can stop the fan when the engine is running. If the fan clutch is weak, it'll stop the fan. If the fan clutch is good I'll try to rip that hose out of your hand. Use extreme caution if you try this!
I'll see if I can see something with your blower in a wiring diagram, later.

 

sweet im gonna do this tomorrow! Thx alot!

 

For your blower fan, you can also check that the ground wire is tight. It should come out of an engine harness and to a bolt or a screw near the cruise control module on the cowl.

 

Yeah, if you can't remember when the last time that your coolant was changed, now is the time to do it. I did mine with a garden hose. I removed the lower radiator hose and had it dump into a bucket. Flushed the radiator out as Hanr3 detailed. I removed the heater core hose off of the water pump to flush out the heater core. Flushed the block out through the t-stat opening. I then used 3 gallons of distilled water to displace most all of the hose water I used, then put in 1.5 gallons of prestone all makes all models antifreeze (big yellow) and topped off the system with distilled water. I washed out my overflow bottle with some simple green, a rag, and some steel ***** from some bearings we had laying around to get it clean. Then filled the overflow bottle with 50/50 mix of the antifreeze and distilled water. All told I used 4 gallons of distilled water, and alittle more than 1.5 gallons of coolant with everything topped off and bled out.

With the fan, you could jumper the relay and see if the fan turns on high. I don't have the schematic in front of me, but IIRC, you'll want to jumper pin 87 to pin 30 (should see the pin #s on the bottom of the relay). Pin 87 should be battery supply voltage through the 30 Amp HVAC fuse (check this fuse first) and pin 30 is the supply line to the blower motor. Ok... Just looked up the schematic for my 2k, should be the same for yours. Pin 87A is the voltage supplied through the resistor pack. Pin 85 is the relay coil ground and pin 86 is the relay coil +12v trigger from the HVAC control head.

Before jumping pin 87 to 30, check the 30 Amp HVAC fuse to make sure that it is not blown. Then check to see if you have +12v on pin 87. By jumping pin 87 to pin 30, it should tell you if its a ground or relay problem. If, when jumpered, the blower motor runs on high, then your problem is either with the relay, or in the relay coil +12v switched trigger (pin 86). You'll also want to check pin 86 for +12v when the key is on and HVAC fan control is set to high. If it does not have +12v, then your problem is between the HVAC control in the cab and the blower motor relay. And by +12v, I mean battery voltage. With the engine off, this could be as low as +11.5v and with the engine on it can be as high as +14.5v.

Also, just to add more info, for the high fan setting, the relay clicks over to supply full battery power to the blower motor. Any other time, the relay is supplying power that comes thru the resistor pack. For Low, it is stepped down through a 0.71 Ohm resistor, a 2.10 Ohm resistor, and a 0.26 Ohm resistor or a total resistance of 3.07 Ohms. For Medium 1, it's only stepped down thru the 2.10 Ohm resistor and 0.26 Ohm resistor or a total resistance of 2.36 Ohms. For Medium 2, only thru the 0.26 Ohm resistor. These resistors limit the power to turn the blower motor giving you the different speeds.

PM me for more information.

 

WHOA. Thats detailed..... lol

I'm gonna have to print tat out and read over it a few times then I should start on it. (if its not to hot out!) lol


Should I really be having this problem at 55k miles? [:@]

 

Ok this is what the Chevy dealer friend says.....

 

Sorry to contradict your friend Dory, but the blower motor resistor simply does not control the high fan function to the blower motor. What I posted above is from the wiring schematic. High function is controlled through the blower motor relay which bypasses the resistor pack to supply full battery power.

As far as the heater core goes, if the temp came down or was managed when he put the heat on, the heater core is functioning properly. Not that a clogged heater core should cause a vehicle to overheat anyway. My old '97 RAM had a completely blocked off heater core and it ran exactly on temp all the time. Cooling systems really aren't all that different between makes either.

If the cap is bad, it could easily cause the truck to overheat. Replace that and make sure you've got the radiator and overflow full and see how things go. If it still overheats, change out the t-stat and give it a good flush.

And electrical components don't really care how many miles are on the vehicle. Same goes for radiator caps, t-stats, or really any other component on a vehicle. They just go sometimes.

 

Is all this common around 55k miles?

 

I would say no, they aren't common problems to be having, but all are affected by rate of use, operating conditions (outside temperature and other factors), and manufacturing defects that may shorten the life of the component. No product is 100% defect free. Just look at the space shuttle.

*EDIT* - And it would never be a bad thing to do a cooling system flush if it is suspected of being problematic, which in your case it is. Especially if it has never been serviced. A 2001 is comin' around to the 5year service limit of Dexcool. I just serviced the cooling system in my bravada a few weeks ago after having the coolant in for over 6 years without being serviced. Clean as new in there.