VEHICLE:
2001 Chevrolet Blazer
4.3L 6 cyl 156k miles on body, 120k on engine

Hello all,

Was reading through a lot of posts about issues with overheating, and it seems everyones problems differed a bit from mine.

I was parked the other night at my girlfriends work, had my car on, AC on, and was inside for about 10 minutes. Came out, got into my car, and noticed a coolant smell. I looked down at my gauges and saw my blazer was at about 240-250 degress.. I freaked, and shut the truck off, as to not let it get hotter. Went to the front and heard a drip, antifreeze was leaking from the over-flow in my reservoir. I pulled the cap on the reservoir and the coolant was so hot, it was bubbling and still spewing from the over-flow.

Left it parked there, went to Oreilly's next day because I knew my Blazer was throwing a code for low coolant/bad tstat. So I went and spent the $10 on a new tstat rated for 195 OE temp. Put it on, refilled with antifreeze, and let her run. Seemed fine all day yesterday. Temperature stayed about 190-195, never went above. Thought cool, its good... Then today, go back to my girlfriends work, went in for 10 minutes, car running, AC on... came back outside, gauge was reading at ~230.... hurried, turn the defrost on, and heat on [95 degree weather] and drove it, and it cooled down.

Anyone know what could suddenly be causing the overheating? what my solutions could be? Had one guy tell me bad water pump, another tell me radiator clogged or bad headgaskets/intake gaskets, or bad fan clutch? I'm at a loss... first major issue ever with the vehicle. Thanks to any that can help!

Here's 2 pictures from today of it after letting it cool down, then driving

This is just after sitting at an idle, and driving off:


This is while sitting at an idle after going into walmart for 5 minutes:


Also, here's a link to a video of the fan spinning. Not sure if it might help or not

http://www.facebook.com/v/218658371589401

 

Well if you replaced the thermostat and no luck simple checks on a cold start run it and see how long it takes to warm up double check your hose running out of your thermostat housing going back to the radiator and see if its getting warm after the guage goes up too 195-205 making sure its pushing fluid through from expirence i have had a few brand new ones go to sticking if heated up too high. If your waterpump was bad more then likely it would be leaking double check the valve underneath the waterpump for leaks when it gets past 210-230 on the guage the hotter the temp the more likely youll find a leak also double check your housing most housing that require a paper gasket i lightly rubb some rtv silicone around the whole thing cause alot of times its in a hard spot to get to to begin with and i don't want to have to do another tear down ever since i have gone to that method i havnt had leaks around there they could be the smallest pin leak but there hard to find unless the engine is heated up with pressure in the coolant system double check for leaks also when you filled up the radiator fluid after the swap did you leave the cap off and let the bubbles get out of the system? before placing the cap back on ive done that a few times myself and all it did was overheat and run out of the overflow. Also the other thing is if you have the orange fluid (dexcool) it tends to gunk up your radiator they recommend you replacing that every 5 years otherwise it tends to cause alot of build up and corrosion. However when doing the bubble check also make sure when its steady level make sure its not sucking the radiator fluid back down otherwise you may have a head gasket leak. Im not for sure about the clutch fan but im guessing if the fans spinning and is engaging when heated up it should be cooling make sure its not disengaging when its getting past 210 i believe it is. Hope some of this helps

Also check your oil dipstick when its getting to the point where you think its getting to hot check that for bubbles if theres bubbles theres a good indication theres radiator fluid mixxing with the oil in which you have a bad head gasket 9 out of 10 times ive had this problem with a gm car overheating tho it checks out good.

 

When its hot check all your hoses to see if they are all hot...if not then you have a flow issue.
These heater cores like to plug up and that could affect flow. Also air in the line will do this.
i had a similar situation last summer...would run for awhile and over heat...thought it was t-stat so i changed it out...no help. It turned out to be the mechanical clutch fan...swapped in a new one and was all good. Before you go that far though check what was suggested above.

 

After reading that & the suggested remidies I'd look at the fan clutch as well. The AC being on is going to make it run hotter, but shouldn't be that much.
I know an air bubble in the system will cause HUGE amounts of grief as Wart said.
Try driving the PS side up on a ramp or elevate it somehow. Take the rad cap off & let it idle to temp (190 or so) & then hold 1000 or so RPM's for a minute or 2. Slowly let off the gas & let it idle a minute. Then rev it back up to 1000 or so.... hopefully this will purge the cooling system of air. Put the cap back on & see how it goes.

 

Quick question; havent done it from a cold start, but just did it after driving and it was warmed up [and at 210 degrees] the fan has great movement, with no restriction. Is this what its suppose to do? or should it stop once i let go? Gonna be pulling the cap and burb this kid once its cooled down, but figured I'd ask about the fan

 

When the engine warms up the heat causes the clutch on the fan to grip more, there for pulling more air through the rad & across the engine.
When it's cold the clutch should have very little resistance & not draw much air through the rad & across the engine.
I've read a couple people say the opposite - that the clutch disengages when hot. Why would it when the rad & engine NEED more air to cool it?!

 

I was in your situation a couple of weeks ago, with the same temperature readings.

Also was ready to replace the fan clutch, an a friend had an idea. We got an obdII scanner and checked the engine temp, and it was much cooler than the gauge told.

The engine was not really overheating, just a faulty gauge.

Check that first, before you start replacing things.

 

I was thinking the same thing with the guage being not accurate however he did state he had low coolant light so more then likely it is getting hot otherwise the pressure wouldnt be so hot its kicking out the overflow causing him to lose fluid i would eliminate that possibility but would make sense tho glad theres people out there trying to help

 

Yeah after the other night, and the coolant boiling over, I'd say the gauge is working good considering coolant has a boiling point of ~250.

 

Got a fan clutch for $50 last night, threw it on there, made quite the difference, takes ALOT longer for it to heat up. Instead of 10 minutes, it took about 30 minutes. still gets 2 clicks over 210 but not as fast. Pulling my radiator today, coolant reservoir, and water pump, cleaning the system thoroughly, and gonna throw it all back together and and put a new wp on, and all new coolant, and see what she does then. did the burp method Rottidog explained, and didn't exactly burp lol so gonna give this all a go today and see what she does