Coolant questions asked and answered

In a previous MACS blog post we discussed Seven reasons why coolants may fail at low mileage. That post led to several interesting questions from Richard in New Zealand, who explained he was “not a mechanic and seeking honest advice.”  To answer his specific  questions, we submitted them to MACS member Dr. David Turcotte, Technical Director, Zerex at the Valvoline Company.

Q.  Does stale engine coolant smells bad?

A. Used coolant often smells bad and can be darkened with time.  Sulfur-containing compounds used for rubber curing can be leached from the cooling system hoses to produce an offending odor.  Small exhaust leaks, fuel, oil and other contaminants can add
to this smell.  Coolant that sits in a bottle for many years probably has no smell.      

Q. As quoted in the service recommendations of a new vehicle:
Engine coolant replace long life coolant at 150,000km( 93,205 MILES ) or 10
years. After first replacement coolant should be replaced at every 75,000km
(46,602 MILES ) or 5 years with long life coolant.
How come before the first change the coolant lasts 93,205 miles/10 years and why after that it only lasts 46,602miles/5 years?

The first coolant change is a very competitive, marketing-influenced point.  The second interval is more conservative and a good engineering approach.

Q. Do you agree with the first change? Does coolant last 93,205 miles/10

If one tops off with the same long-life coolant, maintains the proper dilution, maintains
the cooling system and has good fortune with repairs, yes, the mileage and time
are reasonable.

Q. In New Zealand, radiator experts have to follow the requirements
on the back of a work sheet. It states most coolants lose their protective
properties within 12 months of installation into a vehicle! Do you agree with

While some additives do deplete in service, modern coolants retain their protective
qualities for many years.

Q. If the mechanic changes the water pump before the life expectancy
of the coolant (for example the coolant has done 2 year/33,000 miles), should they reuse the coolant they had drained from the coolant system?

If the fluid is free of debris, particulates and contaminants, properly diluted, correct for
the application, it is OK to reuse it. If your mechanic drained the fluid into a dirty oil pan,
scraped gasket pieces into it and threw a cigarette butt in for good measure, maybe it is time to change the coolant.  If one changes the coolant, it may be the safest action.  Coolant
is inexpensive, engines are not.

Q. On the standard 15,000km (9320 miles) service checks, should the
mechanics be checking the condition of the coolant as well as just topping
up the coolant levels?

The mechanic can only check for fill and proper dilution / freeze protection.  He
assumes the additives are OK and expects that the coolant will be changed in keeping with the manufacturer’s guidelines.

When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.

If you’re a service professional and not a MACS member yet, you should be, click here for more information.

You can E-mail us at or visit to find a Mobile Air Conditioning Society member repair shop in your area. Visit to find out more about your car’s mobile A/C and engine cooling system.

The 32nd annual Mobile Air Conditioning Society (MACS) Worldwide Convention and Trade Show will take place January 18-20, 2012 at the Rio All Suite Hotel and Casino in Las Vegas, NV.


About macsworldwide

Mobile Air Conditioning Society (MACS) Worldwide Founded in 1981, MACS is the leading non-profit trade association for the mobile air conditioning, heating and engine cooling system segment of the automotive aftermarket. Since 1991, MACS has assisted more than 600,000 technicians to comply with the 1990 U.S. EPA Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment. The Mobile Air Conditioning Society (MACS) Worldwide’s mission is clear and focused--as the recognized global authority on mobile air conditioning and heat transfer industry issues.
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