How to drain and refill coolant on C5 Corvette.

Fig. 1 Coolant mixed with distilled water.

Fig. 1 Coolant mixed with distilled water.

Fig. 2 Drain valve detail

Fig. 2 Drain Valve Detail

Fig.3 Draining the coolant. You can see the drain valve and the drain cock here.

Fig. 3 Draining the coolant.

Fig. 4 Coolant filler-cap removed from reservior.

Fig. 4 The coolant reservior fill cap removed.

Fig. 5 Bottle cut in half to use as a funnel.

Fig. 5 Plastic bottle cut and used as a funnel.

Your C5 Corvette requires that you drain and refill the coolant in the radiator every 5 years or 100,000 miles and every 3 years or 36,000 miles thereafter.

In order to do the job, you need three gallons of coolant. (Figure 1.) When you attempt to buy the coolant, you will see two ways Dexcool is offered for sale; premixed and not-premixed. The stuff is $10 a gallon either way, so just buy two gallons of the "not-premixed", and two gallons of DISTILLED water and mix it yourself with the Dexcool.

**NOTE** Make sure you buy distilled water and not mineral water or drinking water.

**NOTE** The GM manual directs you to open the drain-cock and examine the color of the fluid that drains out. If the fluid is clear and clean looking, you are instructed to just drain and refill the system. If, however, the fluid is murky or rusty colored, or brown, you are directed to flush the cooling system. I will document here the drain and refill method only.

If you find your system needs flushed, you can buy a flushing kit at any automotive supply store. You will have to follow the instructions on the kit.

**NOTE** I had the car on a service lift, but you could just as easily slide a pan under the drain-cock and reach in from the top to open the drain valve.

Tools and Materials Required:

Locate the drain valve on the lower passenger side of the radiator. (Figure 2.)

Using a 1/4" drive ratchet, gently turn the drain valve 1/4 turn counterclockwise. If the valve resists turning, use one hand to gently pull the valve outward (towards the rear of the Corvette) while still trying to back it out.

Be careful and gentle with the drain valve, as it is a brittle plastic and is easily broken.

Allow the fluid to drain (Figure 3.) until it slows to a trickle. I get about 10 quarts out of a C5 Corvette when I drain one. The GM service manual instructs you to remove the fill-cap on the radiator reservior before opening the radiator, but I find that I get more fluid out if I leave the cap on.

Close the drain valve by turning the drain valve clockwise until it stops. Do not force the valve. If you have difficulty turning it, try to gently push it in while still trying to turn it.

Remove the coolant reservior fill cap (Figure 4.)

Fill the reservior until the coolant is 1/2" above the full cold mark on the surge tank.

Start the engine and run it for one minute.

Shut off the engine.

Replace the cap on the surge tank.

Start the engine and allow the coolant temp to rise to 210 degrees, and then shut the engine off.

**NOTE** I do not find that it is critical to get to 210 degrees. You are just getting the coolant up to "hot" range for the purpose of topping off the system. In this case, on a 2002 Z06, I was able to put right at 2 gallons of coolant into the cold surg tank. Then, after getting the coolant up to 170 degrees or so, I shut the engine off and topped the coolant surge tank off with about two more quarts of coolant.

Slowly remove the coolant surge tank fill cap and top off the surge tank, again just covering the baffles in the coolant reservior as you see when you look into the filler neck.

You are done! I would check the coolant level after you drive the car a while to ensure that the coolant level is 1/2" above the full cold mark on the surge tank.