Draining automotive coolant.
Cooling System Service and Repairs:

Draining The Coolant On A
1999 GMC Jimmy Or Chevy Blazer



In This Article:

The radiator drain valve is opened with a 1/4" drive ratchet, and the coolant is allowed to drain into a plastic dishpan.

Related Articles:

Skill Level: 2 (Basic) Time Taken: About Half An Hour

By Bruce W. Maki, Editor

Draining the coolant may be necessary for many types of engine repairs. Draining coolant should only be done once the engine has cooled down and the radiator cap can be safely removed.


Do not attempt to open the cooling system if the engine is still hot. Cooling systems become pressurized up to 15 PSI when the engine gets hot enough.

If you remove the radiator cap while the cooling system is pressurized, the coolant in the entire system will suddenly boil and it will blow scalding hot coolant in your face, causing severe burns.

Let the engine cool down until the radiator hoses are no longer firm when squeezed. Just to be safe, place a rag over the radiator cap and turn it to the "first notch" where the cap does not seal the system. If the system was still pressurized, coolant will spray out around the cap but the cap will still be connected to the radiator and you might not get a face full. Sometimes when I do this I can hear a "rumbling" sound from the engine as the coolant starts to boil. If you hear this sound, push down on the cap and tighten it, and WAIT.


Location of radiator drain plug, 99 GMC Jimmy.

The radiator drain plug (arrow) is difficult to see, let alone reach.

This picture is looking almost straight down. The radiator is that black blurry thing on the left.


The radiator drain valve is a couple of inches above the bottom of the radiator, on the passenger side of the car.

I inserted a 1/4" drive ratchet into the center of the drain valve and loosened it about a half-turn. The center of the valve moves outward as it turns, and then coolant flows out through a drain hose.

Radiator drain plug, using ratchet to open.

The picture above is from my article about replacing the water pump, where I had the radiator shroud out of the way. My procedure was basically the same, but I had to use a couple of extensions with the ratchet. My extensions were about 5 inches long. I first inserted the extension into the drain valve, then I connected the ratchet with the extension. I placed the ratchet under the lower radiator hose, where I was able to rotate the ratchet enough to open the drain valve.

Dishpan used to catch coolant when draining antifreeze.

I placed a dishpan under the front of the car to catch the coolant that flowed from the drain hose.


A Closer View:

The drain hose (red arrow) is visible just to the left of the passenger-side tow hook.

Location of coolant drain tube, GMC Jimmy or Chevy Blazer.


Notes On Draining Coolant:

When closing the radiator drain valve, you need to push it inward and then tighten it. When fully closed, there is a small tab on the off-white center part that engages a slot in the black outer part.

After all the coolant has drained, I recommend closing the drain valve before putting all the parts back on the car, because it may be easier to reach the drain.



Filling radiator with anti-freeze coolant mixture.

After all repairs were made, and the drain valve was closed, I placed a long funnel in the radiator opening and poured premixed coolant into the radiator.

It can take a few minutes to refill the cooling system. I filled the radiator until the coolant reached the top, then I waited for the level to go down and added more. After repeating this process until the level no longer went down, I started the car so the water pump would push coolant through the engine and heater core.

Note that complete filling of the cooling system may be impossible until the engine gets hot enough to cause the thermostat to open and push out any air that may be trapped in the upper radiator hose. Many vehicles have a thermostat that opens at 190 or 195 degrees Fahrenheit (87 to 90 degrees Celsius).

On some vehicles I will run the engine for a while and watch the coolant inside the radiator. When the thermostat is closed, the coolant just sits there. Once the thermostat opens I can usually see the coolant moving across the radiator. BUT... the slanted radiator cap on the GMC Jimmy allows coolant to spill out, so I just install the radiator cap to the first "click", which covers the opening but doesn't seal the system.

Air In The Cooling System:

Often after filling the cooling system it's necessary to "burp" the cooling system to get rid of any pockets of air. This can be done by running the engine for a few hours (or even a few days) with the radiator cap turned to the "first notch" which simply holds the cap in place while not forming a tight seal. Turning the radiator cap to the "second notch" forms the tight seal needed for proper pressurized operation.

The Jimmy didn't seem to need any special burping procedures... I just ran it until the thermostat opened, added coolant to the radiator, and then topped up the coolant in the reservoir.

Antifreeze/Water Mixture:

While most mechanics recommend using a mixture of 1/2 antifreeze and 1/2 water, I use 2/3 antifreeze and 1/3 water, which has a substantially lower freezing point (about -60 F versus -35 F). Here in northern Michigan the extra protection can be worthwhile.


Wintertime Cooling System Repairs:

Getting the air out of the cooling system requires running the engine until the it gets hot enough for the thermostat to open. In the winter months, sometimes the engine never gets warm enough for the thermostat to open, especially when just idling or driving gently around neighborhood streets. To make the engine warm up quicker, I'll put the transmission in gear and hold one foot firmly on the brake pedal while revving the engine with my other foot. (I guess they call this a "brake stand".) BE CAREFUL if you do this. I put the car in reverse, so if my foot slipped off the brake pedal I wouldn't crash into my garage door. A smart person would put wheel chocks behind and/or in front of the tires.

Beware... excessive "brake standing" might overheat the automatic transmission fluid. By the way, you can't do this with a manual transmission.

Another pointer: If the car has air conditioning, set the climate control to defrost. Most vehicles will run the air conditioning system when the defrost setting is selected, even if the temperature control is set to maximum heat. By cooling and heating the air, moisture is extracted, just like a dehumidifier. When the a/c runs it taxes the engine and causes it to warm up faster. I always run the defroster after I start my vehicle in cold weather.

More Info:

Tools Used:

  • Ratchet, 1/4" Drive
  • Short Extensions As Needed
  • Plastic Dishpan
  • Long Funnel:

Materials Used:

  • Automotive Anti-Freeze
  • Water

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Written January 8, 2009