So I have been trying to figure this out and would love to get it corrected before winter hits, My Blazer will not heat up to normal operating temperature. It one takes forever to heat up, on temp gauge it will heat to about 210 degrees and then drop the gauge down to about 150~160 degrees.

I have replaced thermostat, lower & upper radiator hoses, flushed coolant system (twice), back flushed coolant system and heater core and on Monday & Tuesday replaced lower intake gaskets, & valve cover gaskets as I was blowing oil out the back of the motor. Also when doing the hoses I pulled the radiator and verified that my radiator was not leaking at all. Also tried burping the coolant system as well to no avail.

Now when I did that job, I flushed coolant system again and refilled with regular green antifreeze.

It still seems like I am getting an air pocket somewhere in the coolant system or some other weird anomaly.

Only other things I can think of are, radiator cap or reservoir cap. Is the reservoir cap suppose to have a seal on the inside? If I tighten mine down I bows out on one side.

Any ideas would be great!

Thanks
pctechdude

 

My blazer was having roughly the same issue. It would take forever to heat up, then it would shoot up to the top of the guage, then drop down to normal, over and over again.

I just plugged a code reader in (I had a service light) and it said
1.) Check coolant Level
2.) Faulty termostat
3.) Faulty/Dirty Coolant Temerature Sensor (CTS)

I haven't dug into the blazer yet as I found this out today and its raining, but I'm gonna check em' all and let you know. Maybe even post some pics.

 

Take another look at your thermostat, I have had brand new aftermarket thermostats stick open on the first use. Also have you verified with a temp guage that the temp isn't coming up, or by turning on the heater. Could be a bad temp sensor and the engine really is warming to temp.

 

the darn bubbles of air are a pain to get out. Did you elevate the passenger side front when burping the system? Also, new rad cap might be in order to make sure you aren't introducing more air into the system. Someone posted a good howto about purging the air (Swartik?) that I followed and was successful with.

My reservoir tank cap has a gasket on it, btw. The symptoms you describe could sound like an air pocket.

 

Back in September, I had to change the radiator on my 1999 s-10 Blazer. I decided to just put water in it until I was sure there were no other leaks. The temperature on the dash was about 195-200. Last week I drained the water and put the green stuff in and the temp dropped to 165 on the dash.