99 Tahoe rad flush

[TC23]

I have 150 000 KMs on my 5.7L and I wanted to flush the rad. Is there anything that needs to be done? I have heard of opening bleeder screws to let the air out and where are these located? I was told you take a hose and hook it up to the rad to clean it out. Any info on how to do this would be appreciated.

Thanks in advance

[sprucegoose]

I am not a big fan of flushing the coolant system myself... Two reasons:

1) It is a PIA because you have to remove the thermostat and cut into one of the heater core hoses to put in a Tee connector for the garden hose. And yes it makes a big mess!

2) It inevidably leaves water from your hose in the system, which will dillute your 50/50 mixture of new coolant.

I just drain the system and refill. Put the rear up on ramps (to get the motor tilted forward for best drainage) and just drop the lower radiator hose and let gravity do the rest. As long as you do this before the coolant goes bad and destroys your radiator or other components you'll be fine. Pull off your overflow jug and hose, and rinse them out well. Also, always mix your new coolant with distilled water so you don't put any minerals in the system...

[97cavalier]

make shure when you refill it you have all the air out of the system.

[sprucegoose]

Originally Posted by 97cavalier

make shure when you refill it you have all the air out of the system.

Good point, I forgot to mention that. There is no "bleeder screw", at least on my 98 anyway...

What I do is fill the radiator up completely (back on level ground now), and then start it up with the cap off. The water pump will suck the level down considerably, and then top it off right away, putting the radiator cap back on. Fill the reservoir to the required cold level, and let the motor idle till the thermostat opens the first time. Watch the temp. gage and it will climb till it reaches about 200F or so, and then it will quickly drop off. A few minutes after that, you shut the truck off and let it totally cool down (at least 1 hr).

The system should suck the level down from your reservoir into the radiator. Add the correct amount to the cold level and now you should be able to drive it. Check it after each use for a day or two, and add more to the reservoir when it is cold if necessary.

[DJ JEFF]

When I recently drained my rad to change the water pump I drained mine and filled it almost exactly like what Spruce says above. The one thing that I couldn't understand was why after the thermostat open and the truck was at operating tempreture, the bottem hose was still fairly cool. The top hose was hot. Could not hold hand on it but for a few seconds. Bottem cool. Drove truck for a while and the bottem hose got warm but not hot.

[sprucegoose]

Originally Posted by 01TahoeJunk

The one thing that I couldn't understand was why after the thermostat open and the truck was at operating tempreture, the bottem hose was still fairly cool. The top hose was hot.

The bottom hose will never get as hot as the top. The coolant is cycling thru the engine in one direction. As the thermostat opens, the hot coolant from your motor goes up out of the top hose and into the radiator. It then siphons back and forth thru the channels of your radiator as it goes down towards the bottom, gradually cooling as the air going across the fins draw the heat away. Then as the thermostat opens again, the water pump sucks this coolant from the bottom of the radiator back into the engine to begin the process again.