Trailblazer overheating

I'd suspect air is trapped in the cooling system. Hope that helps! Jim

I suspect that as well but the shop said they used an air lift to fill it which vacuums the system and releases the coolant to fill. But there could be air trapped by the new tstat. The heater still blows hot so it's getting flow through there. I'm at a loss because the hoses still feel super squishy like it's not pressurizing. But that would mean it's got a leak and it's not loosing fluid.

Using a $3 hydrometer, check to make sure the coolant is a 50/50 mix. I just had this problem, my mix was around -19 degrees. A 50/50 mix should read -35 degrees on the meter. If you need more concentrate, add it. There is a drainplug on the passenger side of radiator at the bottom, to make room for more concentrate. Run it with the cap off for as long as you can, I even shook my TB violently to get as much air as I could out. FYI, the stat only goes one way, can't install it incorrectly. If you're in N. CA, I'll help ya.

I'm in Denver area. I've got a neighbor who was a master mechanic for 30 years. He does think it's getting any flow. Like the tstat isn't opening or the pump is bad. Which both are new parts so they should be good. I'm just getting a run around from the shop.

I haven't seen any bad pumps out of the box, but I have seen bad stats out of the box. Along with bad fan clutches (many of them) out of the box for our platform. Try running it without the cap, shake the vehicle, try to get all the air out. Or use a jack and lift the front passenger side up high, that's another method of getting rid of air. Worth a shot, and it's free. I just went through my tranny cooler that burst inside of my radiator. I had to start from scratch, get all air out, and make sure mixture is 50/50 on my own Trailblazer.

By the way...... I had air in my system too, hoses were squishy until I got it all out, using the methods above. Hard as a rock now.

Double check your belt routing. Some water pumps are reverse rotation. In other words they spin the opposite direction of the crankshaft. Hope that helps! Jim

I went and washed the radiator out. I jacked the front right up super high and ran it for 30 min with the cap off. The hoses feel better but it's still overheats going uphill or when the AC is on. If I run it with the heater it stays at 210 which has been it's normal for the year I've had it. If it's just idle with AC it doesn't do that.

I've also replaced the radiator cap and checked the belt as recommended above. Starting to think maybe it's the fan.

Oh and spent the entire 30 min checking temps of hoses, block and overflow with an infared temp sensor. The two hoses were average 18° difference after stat opened. Never got more than 50° difference.

This is a coolant circulation problem. Or, if this is a high mileage vehicle you might be looking at a worn timing chain or a problem with the distributor, if equipped. A worn timing chain will cause the valve timing to be retarded (late) and will cause the engine to run hot. Especially under load. Same is true if the electronic advance mechanism is not working in the distributor. You have good airflow or it would be overheating at idle. So it's not going to be the fan. Hope that helps! Jim

One other thing, if the engine has a valve tap or other noise the knock sensor may be picking it up and sending a signal to the computer to retard the ignition timing. Hope that helps! Jim