Mag Chloride vs Road Salt on Your Car in Frederick

Mag Chloride vs Road Salt, Side by Side

Both are chloride salts. Both melt ice by lowering the point where water freezes. The difference is in how they act once they land on your car.

	Mag chloride	Road salt
Form near Frederick	A liquid brine from CDOT trucks and the Firestone crews	Granules, like the Ice Slicer that Frederick spreads
When it goes down	Before and during a storm, to stop snow from bonding	Early in a storm and on packed snow
How it acts on metal	Sticky. Dries into crystals, then pulls in water again	Washes off more easily, but soaks parts that sit in slush
When it does the most harm	Damp air, the dry and wet swing of a Front Range winter	Parts that stay wet, and dry air in the lab tests
Where it hides	Seams, brake lines, frame rails, wheel hubs	The same places, plus slush packed in the wheel wells

So the useful question is not which one is gentle. It is how long either one stays on the metal. That part is up to you.

What Goes on the Roads Around Frederick

You drive on three road owners in a normal week here. Each one treats the road a little differently.

State highways. CDOT runs I 25, SH 52, SH 66 and SH 119. In its 2012 winter release for the Boulder, Longmont and Estes Park crews, CDOT said it used liquid mag chloride above a pavement temperature of 16 degrees. Below that it used a cold weather mag chloride with a corn byproduct mixed in. It also spread Ice Slicer and salt granules, often on curves and intersections. That release counted about 171,708 gallons of liquid deicer and 1,708 tons of solid deicer for those crews in one winter.

The same release listed automatic deicing systems on SH 52 and SH 66 where they cross I 25. It also listed three on I 25 between Weld County Road 20 and SH 66. That is the stretch right past Frederick.

Frederick town streets. The Town says its plow trucks spread ice slicer granules early in a storm, sometimes with the blade up. The town looks after about 104 miles of streets. The Ice Slicer data sheet that Longmont posts lists it as 90 to 98% sodium chloride. That is road salt by another name.

Firestone streets. Firestone says it sprays mag chloride when the forecast shows a 50% or better chance of snow. It may spray again on packed snow after a storm. Then its plows lay down granules once 2 inches build up.

So a trip from a Frederick cul de sac to I 25 can pick up both kinds in ten minutes.

Which One Is Harder on Your Car

CDOT paid for a study on this exact question. University of Colorado Boulder researchers published it in May 2002. They tested both salts on steel, stainless steel, aluminum, coated body panels and copper wire.

The tests did not agree at first. One method showed mag chloride as worse on bare metal. Two others showed salt as worse. So the team dug into why. Their answer was moisture.

• Mag chloride is thicker and pulls water out of the air more strongly.
• It sticks to metal and dries into crystals.
• When the air turns damp, the crystals melt back into a wet film.
• That cycle made mag chloride the worse one in humid conditions.
• Salt was the worse one when parts sat under water, and in dry air.

After the study, CDOT changed its buying rules. The mag chloride it buys has to be no more corrosive than salt on aluminum and stainless steel, in one standard lab test.

That rule is good news, but read it closely. It covers two metals in one test. Your brake lines are coated steel. A gentle label on the tank does not mean the film under your car is gentle.

Where It Does the Damage

Brine does its work where it can sit. Those are the low, hidden parts that rain never rinses.

Part	What to look for	Why it matters
Steel brake lines	Flaking, swelling, rust that is thick and scaly	A line that leaks can drop the pedal to the floor
Rubber brake hoses	Cracks near the metal ends	Fittings rust and hold the hose tight
Caliper slides	Uneven pad wear side to side	A stuck slide wears one pad fast
Parking brake cable	A lever that feels stiff or will not let go	Rusted cables bind in the cold
Frame seams and rails	A white crust after the snow melts	Brine packs in seams and stays wet

Brake line rust is a slow problem. Federal safety regulators studied brake pipe failures in about 2 million GM trucks and SUVs sold in their list of salt states. Complaints ran under 0.1 per 1,000 trucks at 7 years. They climbed past 1.0 per 1,000 after the 12th year. Most of the failures came on trucks more than 10 years old.

NHTSA closed that case in 2015 without a recall. It said the coating wore out under harsh road conditions. Then it told owners to wash the underside and have the lines checked.

A Winter Rinse Plan for the Front Range

1. Rinse the underside, not only the paint. Pick a car wash with an underbody spray, or use a garden hose on a warm afternoon. Aim at the wheel wells, the frame rails and the lines along the frame.
2. Do it after a storm cycle. NHTSA says to wash the underside regularly all winter. It does not give a number. Once the roads dry out and the day climbs above freezing is a good time.
3. Let it dry before a hard freeze. Water locked into a door seal or a lock on a cold night is its own problem. A short drive after the wash helps.
4. Clean it well at the end of winter. NHTSA calls for a full underside clean when the season is over. Wait until the last spring storm has passed.
5. Get older cars looked at twice a year. NHTSA says older cars in cold weather states should get a check at least twice a year. If rust turns up, check again at every service.
6. Look for yourself. Lie on a mat with a flashlight. Find the thin metal tubes that run from the master cylinder to each wheel. Scaly or swollen spots are worth a call.

Common Misreads

Colorado does not salt its roads. It does. CDOT lists salt granules right beside its liquid brine. Frederick spreads Ice Slicer, which its own data sheet lists as 90 to 98% sodium chloride.

Mag chloride is 70% less corrosive than salt. That line comes from an August 2002 Summit Daily story about the CDOT rule of the time. The CDOT study out that May had already found mag chloride worse in humid conditions. The rule that came out of the study asks only that it be no worse than salt on two metals.

The salt belt is back East. On paper, yes. NHTSA's list of salt states for its brake line case named 20 states and Washington, D.C. Colorado was not one of them. Your brake lines do not read that list. They react to what is on them.

Dry air protects you. Not from mag chloride. The study found it pulls water out of the air and goes wet again. A sunny Front Range week after a storm keeps that cycle going.

When a Line Looks Bad

A rusty line can look solid and still be thin. Do not pick at it with a screwdriver to test it. A line that fails under your thumb fails at a stop sign, too.

Watch for these signs on the road.

• A pedal that sinks slowly while you hold it at a light.
• Wet spots inside a wheel or under the car near a wheel.
• A brake warning light on the dash.
• A low level in the brake fluid tank under the hood.

A sinking pedal is a leak, not worn pads. That car should not be driven anywhere.

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