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Orange vs green: coolant basics you need to know

Understand the difference between coolants, and how to look for problems

Editor's Note: This article was originally posted in 2009. On GM's own consumer site, the debate regarding its Dexcool antifreeze continues. And in mixing any antifreeze with water for a 50/50 mix, the use of distilled water is highly recommended.

What is coolant?

Coolant (sometimes referred to as antifreeze or radiator fluid) is used to regulate your engine temperature and prevent it from overheating.

Can I mix green coolant with orange coolant?

This is one of those questions usually asked after the fact, and usually engine damage has already occurred. The green and orange coolants do not mix. When mixed together they form a gel-like substance that stops coolant flow, and consequently, the engine overheats.

There are some coolants that claim compatibility with Dexcool, but I would rather err conservatively and add what the system is supposed to take rather than gamble. To guard against major engine failure, read on.

What exactly happens when these coolants are mixed?

The coolants chemically react and form a gel rather than a liquid. The coolant stops flowing through the system, clogs up coolant passageways and water jackets, radiators, and heater cores. The water pump overheats and fails due to a lack of lubricant in the coolant. Head gaskets blow, heads warp, and the engine suffers major damage.

If I have Dexcool in my car, can I leave it in for the life of the car?

GM suggests flushing Dexcool for the first time at 150,000 miles.

What exactly is Dexcool?

In the 1990s, GM introduced an engine coolant called Dexcool. It's supposed to last 5 years or 150,000 miles, but there have been problems with this coolant. Cooling systems that use Dexcool exhibit more acid buildup and rust in the system when the coolant level gets low and oxygen is allowed to enter the system. The acid eats away at head gaskets and intake gaskets. Rust builds up in the system, inhibiting coolant flow, which causes overheating.

Overall, numerous cooling system problems have been attributed to the use of this controversial product, although GM firmly stands behind it. There were class action suits against GM on this issue, and GM reached settlement agreements with some owners beginning in 2008.

So what are the guidelines on maintaining engine coolant?

Here's the bottom line when it comes to cooling system maintenance. Whether you are running Dexcool (the orange stuff) or ethylene glycol (the green stuff), inspect the coolant level and the condition/protection of the coolant at every oil change. In addition, completely flush and refill the system every two years or 25,000 miles, whichever comes first. These actions will avert the problems associated with Dexcool or any other coolant product.

Watch for signs of oil or rust.

The color of healthy engine coolant is green (for ethylene glycol) or orange (for Dexcool). A rusty color indicates that the rust inhibitor in the coolant has broken down and it can no longer control rust and scale buildup. The system must be cleaned/flushed and a fresh 50/50 mix of coolant installed to restore integrity.

A milky color indicates the presence of oil in the system. This is not good; it usually means that a head gasket, intake manifold, or transmission oil cooler is leaking oil or transmission fluid into the engine coolant. This is a deadly mix that will kill an engine or transmission in short order. Address the probleFrim immediately!

Slippery coolant is a sign of good coolant.

The engine coolant should feel slippery to the touch and smooth (like the engine oil). If it feels gritty, the coolant is dirty and should be flushed and replaced with a fresh 50/50 mix. If the coolant does not feel slippery then it has lost its lubricity (the lubricating and rust inhibiting agents have deteriorated) and the system is at risk for rust and scale buildup, as well as water pump wear.

Use your nose.

Change the coolant if it smells burned. Also change the thermostat; it's probably gone bad because it was exposed to overheating (or it caused the overheating). Overheating damages the bi-metallic spring that opens and closes the thermostat valve. Most importantly, find out what caused the system to overheat and repair it to avoid major engine damage.

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