If you're overheating while moving then the fan clutch has nothing to do with it. It's only purpose is to draw air through the radiator while the vehicle is stationary. The fan clutch should not spin freely but provide some resistance when you turn it by hand. It's purpose is to turn while idling but when the engine RPM's increase it slips slightly so it acts as a rev limiter reducing the fan noise. Swartikk mentioned something about it increasing tension with the heat of the engine..I'll take his word for it as he knows just about everything there is to know about these engines. I'm pretty much working from my own experience living both in Arizona and Florida where your cooling system must be operating at 100%.

Check your radiator after the car is warmed up. Stop the engine and feel top to bottom on the radiator. If it's hot on top and cool on the bottom that means you have crap blocking the lower passages. If you look inside your radiator you'll see little horizontal slits where the water flows. It doesn't take much for them to get blocked. If a chemical flush doesn't clean it out you'll have to replace the radiator which is what I wound up doing. Mine most likely got clogged by mixing regular coolant in with the original DexCool which I'm told tends to create globs.

The other symptom you had was a collapsing return hose. When the engine heats up the coolant expands building up to 16lbs of pressure. The excess pressure and coolant flows into the reserve reservoir As the engine cools a slight vacuum is produced which is supposed to draw coolant back from the reserve tank. If your hose is collapsing that would indicate to me excessive vacuum which could be caused by a leak, weak hose, bad radiator cap or the reservoir line is plugged. When you opened the cap it let air in which relieved the vacuum. You were asked if you were loosing coolant but I didn't see a response. Also you mentioned 185 degrees ...the 4.3 thermostat should be 195 degrees which is required for proper engine operation.

 

Read AGAIN what dobyken said.

The flat hose is a dead giveaway! The rad cap only allows coolant TO the reservoir at 16lbs or above. The cooldown scenario says the cap will draw FROM the reservoir at minimal vacuum.. certainly LESS than required to collapse that hose, unless it's really weak.

Therefor you have a kink in the hose to the overflow bottle or the bottom of that bottle is filled with crap. What does the bottle look like inside.. lots of 'brown sludge? -sigh-


However you may have another problem, too. It's conceivable that unable to refill from the overflow it's sucking air from somewhere else.

Wife's bravada is not here right now so I cant look.. have you checked the rad when cold? It SHOULD be to the cap level.

Another possibility is bad head gasket taking cylinder gases to coolant passages. Very common for head gasket fail. but dont get in a panic till you solve the 'fail to draw back overlflow' problem.

 

So I worked a little on my Blazer this afternoon and cleaned up the coolant reservior. There was a bunch of gook at the bottom of the return opening so I took a pipe cleaner to it and cleaned it up. I also cleaned up my rad cap a bit. I cant tell if the cap is bad. Whether that is the problem and solution or if its just a part of the cause. I haven't had the opportunity to run a true test on it by driving it and letting it cool for 5 minutes and driving it again. Im hoping that will take care of it.

Im going to be keeping an eye on the upper rad hose to see if it collapses again. I did realize after a few of the posts since yesterday that I know that no coolant has either entered or exited the overflow.

As a correction, my Tstat is the 195 rather than the 180 that I previously posted. I couldn't remember the degree when I made my initial post. I also am thankful for you guys, I honestly wouldn't have thought of most of the stuff that you all have brought to my attention.

 

Hoses should not collapse. I would replace the hoses and the cap. Very cheap preventative maintenance.

 

like they said air in your system or the thermistat is going bad.

 

guys, may I ask where I can obtain this T adapter for the heater core hose so I can bleed air out of my coolant system??

thanks

 

Radiator flush kit, at all parts stores. Less than $15.00 for the kit.
Example:Help/Universal radiator flush kit includes 2 pcs. clamp and 1 pc. each of 5/8 x 3/4 in. T, garden hose adapter, elbow and cap (47018) | Radiator Flush | AutoZone.com

 

^^^ I would do as kristoph said, I can almost guarantee replacing the rad hoses and cap will fix your problem.

 

Mike, I have that already but it doesnt have a bleeder.

 

The first thing you should try is elevating the front of the truck a few inches then running the engine with radiator cap off for about 20 minutes after reaching operating temperature. That should burp the air from the system. The "T" adapter is for flushing the cooling system but I have used it a couple of times to pump coolant into the engine on babies that didn't want to burp.