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7 reasons why coolants may fail at low mileage

With all the long-life coolants, and even the three-year/50,000 mile conventional coolants, it’s fair to ask: why do we see so many cases of coolants failing at low mileage. The obvious reason, of course, is that we’re in the business. Unless there’s a vehicle problem that brings them in, people with healthy cooling systems don’t stop by and say, “My cooling system seems to be working just fine.”

What are signs of failure? The most common:
debris, including rust in cast-iron systems;
leaking heaters, evidence of plugged heaters or other restrictions,
overheating, perhaps even an occasional case of electrolysis (unacceptably high voltage in the coolant), leading to degradation of hoses or heater.
Add in a couple of general issues, although not frequent: antifreeze concentration and core sand.
Sometimes the factory fill is just weak, well under 50/50. So just because a vehicle is only a few years old and has never had a leak, don’t assume the factory fill is at specs. You’ve got to check, and here is a related problem: what do you use to check?
Except for laboratory equipment and lab procedures, the refractometer(see photo above) has logically been touted as the most accurate choice, and the hydrometer as the least accurate. Dip-type test strips have their fans, but our experience is they are not consistently accurate as indicators of freeze protection. So we stay with the refractometer as our No. 1 choice, and have not picked a No. 2.
Core sand is an issue that’s been around for a long time. With today’s precision molding, you’d think core sand would be history, but sometimes the release of the casting from the sand mold is not perfect, and some sand residue may end up in the engine. The heads and blocks are washed at the factory, but still we see the problem, and flushing with a machine is the only practical service fix.
Molds are usually allowed to air-cool before the release from the casting, but there are engine-manufacturing plants where the molds with castings are liquid-cooled to speed up the process, and this seems to result in a change in the surface of aluminum castings. The surface of the cooling system passages with this casting system may require a tailored antifreeze inhibitor package, therefore be more likely to corrode with other antifreeze formulas, according to one coolant chemist to whom MACS spoke. If so, it would be a good argument for not mixing types of antifreeze.
Cast iron is anything but history. When a purely organic acid technology (OAT) antifreeze is used and coolant level is low, rust can form on the cooling passage walls, and the rust may be washed into the radiator, where it causes plugging. This is what we saw when General Motors engines suffered the problem, as a result of a radiator cap vacuum valve issue on systems with DEX-COOL.
OAT antifreezes in general are not as heavily buffered as other types, so if the pH drops below 7, the cast iron may rust more severely.
Even with aluminum engines, a big drop in pH can result in a corrosion problem, the coolant chemist said, if excessive Nocolok flux is used on a CAB radiator (controlled atmospheric braze). Although the flux is inert, an excessive amount can produce a glassy residue that dissolves in OAT (and even hybrid OAT) antifreeze. This can lead to formation of fluoride, which affects additives and causes corrosion, he said. This possibility is a good argument for sticking with reputable radiator suppliers.
And if the problem follows a recent coolant change, perhaps the most likely cause is failure to get out enough of the old coolant, from the drain or flush.
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.
You can E-mail us at or visit to find a Mobile Air Conditioning Society repair shop in your area. Visit to find out more about your car’s mobile A/C and engine cooling system.
Thanks to MACS member SPX Robinair for the photo of the refractometer pictured above.

3 responses to “7 reasons why coolants may fail at low mileage”

  1. David Folts says:

    We have an older 4 cylinder Dodge Van with high miles. It runs well but I did find a problem when getting ready to change the coolant. We saw a white/gray paste about 1/16 – 1/32 of an inch built up on the surfaces on the radiator when looking down into it. This coating was fairly uniform occaisionally having higher mounds. The consistency was that of a paste when rubbing it between your fingers. The van does not overheat. Some of it must have built up at the drain cock because when we turned the drain cock handle 90 % the radiator would not drain. Tried to run a wire up through the drain cock but would not work due to the design of the drain cock. Ended up draining the coolant through the 3/8 inch plug in the engine block. We bought the van used so do not know if someone added a additive to the radiator. There isn’t any leaks in the system. Would a commercial flush added to the radiator clean this out.

  2. Here is a reply from Hecat a MACS member who specializes in flush machines
    Always check for any TSB’s regarding cooling systems buildups and/or clogging heater cores. The white and gray color pasty buildups first make me think of oil in the cooling system; so a good check for a cracked head, head gasket, Trans oil cooler (although it would be pink), etc. type of problems.
    Second thought is that some cooling system sealers do also have this color.
    The drain cock clog makes me think there may be more buildups (sediment, sealer, etc.) than most commercial flush chemicals would resolve (although it would not hurt to try), and a powerful flush of the separated primary
    components (radiator, heater core, and engine block) may be required.
    Karl Matis
    HECAT, Inc.

  3. Richard Ervine says:

    I am in New Zealand. I would really appreciate if you could answer my questions. As quoted in the servcing recommendations of a new vechicle. 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 QUESTION IS 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?
    QUESTION IS do you agree with the first change it lasts 93,205 miles/10 years?
    QUESTION IS 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 installion into a vehicle! do you agree with this? QUESTION IS If the mechanic changes the water pump before the life expentancy 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. QUESTION IS On the standard 15,oookm(=9320 miles) service checks should the mechanics be checking the condition of the coolant as well as just topping up the coolant levels?
    QUESTION IS Does stale engine coolant smells like urine? I am not a mechanic and seeking honest advice. Thanking you Richard