Coolant leak on a 2006 trailblazer from underneath the engine. what could possibly be a cause

booster failure .

The thermostat is a possibility. If it is not opening to its fully open position when the coolant reaches normal operating temperature, then it could cause the engine to overheat. Probably something that should have been changed along with the water pump. You mention several good possibilities. The important question is does it require adding coolant? Or have you driven it enough to tell yet? Only two ways it would require additional coolant: either it is leaking or it is boiling away. The best way to check for leaks is with a pressure test. There are many places where the coolant can leak internally in the engine or externally, and none are good. Check your oil dipstick for coolant mixing with the oil, a sure sign of head gasket or intake manifold gasket failure.

The sensors could be seen on a scan tool capable of showing live stream data, and should quickly show if they are operating normally or are out of range. Sorry I don't have an answer on how to test the fan clutch-it may be a simple test, too. I'm pretty sure the fan blades should be free wheeling, with the engine off, fan not running.

check for a bad head gasket, radiator, hoses etc. or a bad soft plug. if water in oil headgasket is bad!!

You have a small leak on the rear of engine whioch is difficult to see. Run the engine to operating temperature. Put it on a ramp and examine from underneath with engine idling.

Yes it can, the coolant leaks from the heater core, and causes the engine to lose coolant. The sad part is, if your heater core in underneath your dashboard, you will have coolant in the floorboard.

Check your coolant level, low coolant or air in your cooling system will make a "thud"noise in your heater core when the engine is under load from acceleration. The coolant rushes in to the heater core where the air pocket is trapped and then your hear the noise.
Start with the simple and make sure your coolant level is correct and then try to purge the system to remove the air out for your coolant system.
Thank you for using fixya and good luck

Depends on what the "fluid" is. If it is brake fluid or gasoline or coolant you have a serious problem that must be fixed immediately. Gasoline is expensive and a fire hazard. Brake fluid implies that the brake system needs attention. If it is coolant and the vehicle has a rear heater there could be a leak in the heater core or the lines that run from the engine compartment to it. If it is plain ordinary water and the vehicle has rear air conditioning it is just the condensate that is produced when the rear air conditioner runs. It is normal and is no cause for concern.

The belt should be on an automatic tensioner ,your problem is not in the belt but it is possible you have air in the coolant system and the coolant sensor is not submerged and therefore will not allow engine to reach maximum rpm's,try running engine up to temp while the coolant cap is off and wait for all air to come to surface.that should solve you problem. good luck.

I HAVE A 2006 CHEVY TRAILBLAZER AND NOTICED THIS WEEK IN THE EXTREME COLD AFTER I HAVE LET THE TRUCK WARM UP IN THE MORNINGS THERE ARE SMAL PUDDLES OF ANTIFREEZE THAT IS LEAKING IN FRONT. AFTER I DRIVE IT I HAVE NOT NOTICED THAT IT IS STILL LEAKING AND THE TEMP IS NOT GOING UP WHILE I DRIVE THE TRUCK. WHAT COULD POSSIBLY BE WRONG?

you are loosing engine coolant, and it
can be related yes!

G