2000 Catera - Stumped on an overheating issue

[Elo]

Hey guys, having a weird issue with my Cat that's really got me stumped. Hopefully someone can help me out.

I was driving home from work about 2 months ago when I noticed the temp gauge starting to climb pretty quickly. I pull over and notice I'm pouring out coolant. I look, and the radiator has cracked in the plastic near the upper radiator line.

Fast forward to this past Saturday...

I get the new radiator installed, the coolant refilled, and then fire the car up. No more coolant leak (hooray!), but the temp gauge kept on climbing. The air coming out of the heater would be hot, then it would cool off. Knowing that this is a symptom of an air block, we burp the system to get all the air out. The heater constantly blows hot air at this point, but the car still overheats. We also notice that the fans never once came on.

We proceed to pull every single fuse and relay that we can find and test them out using a DMM. Everything was fine in those regards, so now we're stumped.

Thoughts on what I should look into next?

[CateraMV6]

makes me wonder if the thermostat is stuck close... does the water ever flow through the radiator once it reaches 198°F... and if it does then the thermostat is good...

After that you can look at the coolant sensor that tells the ECU how hot the car gets and then based on that it turns on the fans...

Try holding the hose from the block to the radiator and see where it opens... of course have someone look at the temp gauge to see what the temp is on there...

Another thing is the TEMP Sensor may have gone bad and it could be reading too high of a value.... I would hook up a scan gauge and try to see what Coolant temps the ECU is seeing!...

Then go from there...

Also check all hoses, because I had an old car where the bottom hose was not tightened properly and no matter how many times we tried to evacuate the air out of the system ass soon as the thermostat opened the car sucked air from the bottom hose but didnt have any leaks and it bothered me for months...

[Elo]

Originally Posted by CateraMV6

makes me wonder if the thermostat is stuck close... does the water ever flow through the radiator once it reaches 198°F... and if it does then the thermostat is good...

After that you can look at the coolant sensor that tells the ECU how hot the car gets and then based on that it turns on the fans...

Try holding the hose from the block to the radiator and see where it opens... of course have someone look at the temp gauge to see what the temp is on there...

Another thing is the TEMP Sensor may have gone bad and it could be reading too high of a value.... I would hook up a scan gauge and try to see what Coolant temps the ECU is seeing!...

Then go from there...

Also check all hoses, because I had an old car where the bottom hose was not tightened properly and no matter how many times we tried to evacuate the air out of the system ass soon as the thermostat opened the car sucked air from the bottom hose but didnt have any leaks and it bothered me for months...

At first, it didn't seem like we were getting flow through the radiator since it wasn't getting hot. After we bled the air out, the radiator did get hot. This was also when I had constant hot air. The thermostat is definitely something we are considering, but weren't sure with everything else.

Do you happen to know which sensor it is that tells the ECU how hot it is? Is it one of the two sensors that are plugged into the driver-side of the radiator?

I'll see what I can do about hooking up a scan gauge.

Also, I forgot to mention in my first post that if we hot wire the fans to the battery, they run. So I think you may be on to something with a sensor issue.

[lakesidepark]

I 'think' the sensor at the radiator controls the fans, and the sensor on the coolant bridge reports to the ECU.