2002 Chevy Tahoe How to Flush the Coolant System

  • V8
  • 2WD
  • 150,000 MILES
I started to drain the coolant system for a system flush and could only get about 7 of the 14 quarts in the system to drain out. I poured the coolant back in until I figure out what's up, and the system shows to be full.

What do I need to do other than removing the reservoir cap and opening the drain valve?

I removed the upper radiator hose and it did not help.

I started the engine and ran it until the engine reached temperature - still nothing additional came out beyond a trickle.

I started this exercise because the system started running about 245 F under highway loads, and I thought the thermostat was stuck. Is the trickle I'm getting the flow through the thermostat air bleed valve?

How should the draining normally be done?
Sunday, May 10th, 2009 AT 10:50 PM

1 Reply

  • 1,482 POSTS
In order to totally drain all the fluid out of the system you must remove the soft plugs in the engine block. The radiator holds about 1/2 of the coolant in the system (when full and running) and the engine block holds the rest.
To totally flush the system - remove the thermostat - drain the coolant in the radiator only - then put in some coolant system flush (prestone is the best) - and fill it up with DISTILLED WATER - run the engine (without a t-stat) as directed in the instructions of the flush. Then drain all the coolant out by first draining the radiator - then filling with regular water - run for a while - drain coolant from radiator. Keep doing this until the coolant is all water.
Next - drain as much water out as possible by removing the upper and lower radiator hoses and the radiator drain plug (as usual) - install a NEW thermostat - add coolant and be sure to mix coolant with DISTILLED WATER or just buy pre-mixed coolant.

I do not recomend removing the soft plugs in the engine block to drain coolant - unless you are rebuilding the engine. Flushing the system is the way to go.
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Tuesday, May 12th, 2009 AT 4:21 PM

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