Cor­ro­sion: silent killer of ve­hi­cles

Winnipeg Free Press - Section F - - AUTOS - JIM KERR

WITH our busy lives, it’s easy to over­look some ve­hi­cle main­te­nance items, such as chang­ing the en­gine coolant. If it’s still work­ing, ev­ery­thing must be OK, right? Wrong. Cor­ro­sion is a silent killer of ve­hi­cles. By the time we can see cool­ing-sys­tem cor­ro­sion, costly re­pairs are of­ten needed.

A cool­ing sys­tem is a com­plex as­sem­bly of com­po­nents and ma­te­ri­als. Alu­minum, cast iron, steel, stain­less steel, cop­per, brass, rub­ber, plas­tic — an en­gine coolant must be com­pat­i­ble with all of them. The coolant must also trans­fer heat ef­fi­ciently, stop cor­ro­sion and pro­vide lu­bri­cant for water-pump seals.

This task doesn’t sound too hard un­less you re­al­ize that any time two dis­sim­i­lar met­als (such as dif­fer­ent alu­minum al­loys) are placed in con­tact with an acidic liq­uid (used an­tifreeze), you have a crude bat­tery. Elec­tric­ity gen­er­ated by the cool­ing sys­tem causes ac­cel­er­ated cor­ro­sion of the ma­te­ri­als. Chang­ing the coolant when re­quired will pre­vent ex­ces­sive acidic build-up in the sys­tem and help pre­vent cor­ro­sion.

Three types of an­tifreeze are com­monly used in light-duty ve­hi­cles. Ethy­lene gly­col has a sweet taste, but even a small amount can be fa­tal to small an­i­mals and chil­dren so care must be used when stor­ing or drain­ing it.

Propy­lene an­tifreeze is less toxic and has a slightly bit­ter taste, so it’s less at­trac­tive to an­i­mals, but care should still be taken to store it safely. Both ethy­lene gly­col and propy­lene gly­col con­tain sil­i­cates, phos­phates and/or bo­rates as cor­ro­sion in­hibitors to keep the coolant so­lu­tion al­ka­line. Th­ese an­tifreezes are typ­i­cally green in colour.

A third type of an­tifreeze is also ethy­lene gly­col-based, but con­tains or­ganic acids that pro­tect the en­gine from cor­ro­sion. Gen­eral Mo­tors started us­ing this an­tifreeze un­der the Dexcool name in 1996. It has a five-year/160,000 km life­time ver­sus the two-year life of most other an­tifreezes. This “long-life” an­tifreeze is or­ange in colour, but don’t be fooled by or­ange or red coolants in non-GM ve­hi­cles. Check the owner’s man­ual to see if it should be changed at five-year or two-year in­ter­vals.

Don’t mix long-life and reg­u­lar an­tifreeze to­gether or the life of the an­tifreeze will be short­ened to two years. If you have to add an­tifreeze, mix it with water in the ra­tio shown on the con­tainer. Some come pre-mixed, but most rec­om­mend a 50/50 mix­ture (some cheaper ones are 60/40).

A low coolant level in­di­cates a leak. If there are no vis­i­ble stains or cor­ro­sion on the out­side of the en­gine or com­po­nents, the coolant could be leak­ing in­ter­nally into the en­gine oil. This can dam­age en­gine bear­ings quickly, so have it checked out as soon as pos­si­ble by a me­chanic.

The most en­vi­ron­men­tally friendly way to change an­tifreeze is to take the ve­hi­cle to your lo­cal re­pair shop. Most shops now use an­tifreeze re­cyc- ling machines to flush the cool­ing sys­tem, clean your old coolant and fill the ve­hi­cle with re­ju­ve­nated coolant.

Dur­ing a cool­ing-sys­tem flush, the old coolant is re­moved from the ve­hi­cle into the re­cy­cling ma­chine, and then water is forced through­out the sys­tem and drained. Next, the old coolant in the ma­chine is fil­tered and tested for its strength (freez­ing point) and its pH bal­ance. New an­tifreeze is added if nec­es­sary to in­crease the coolant’s strength.

An ad­di­tive is used to bal­ance the pH level of the coolant so it’s no longer cor­ro­sive and a chem­i­cal package con­tain­ing ex­tra cor­ro­sion-pro­tect­ing ma­te­ri­als and water-pump lu­bri­cant is added. Then the re­cy­cled coolant is pumped back into your cool­ing sys­tem.

While an­tifreeze coolants do pro­tect the en­gine from freez­ing in cold weather, their abil­ity to pro­vide heat trans­fer and raise the boil­ing tem­per­a­ture in hot weather are just as im­por­tant to en­gine dura­bil­ity. Com­pared to water, with its 100 C boil­ing point, a 50/50 mix­ture of an­tifreeze and water has a boil­ing point near 130 C.

Clean, qual­ity an­tifreeze mixed in the cor­rect pro­por­tions with water will pro­tect your cool­ing sys­tem from cor­ro­sion and help pro­tect your en­gine from over­heat­ing. So don’t over­look ve­hi­cle main­te­nance that is at the bot­tom of your “to do” list. Jim Kerr is an ex­pe­ri­enced me­chanic, in­struc­tor of au­to­mo­tive tech­nol­ogy, free­lance jour­nal­ist and mem­ber of the Au­to­mo­bile Jour­nal­ists’ As­so­ci­a­tion of


While an­tifreeze coolants do pro­tect the en­gine from freez­ing in cold weather, their abil­ity to pro­vide heat trans­fer and raise the boil­ing tem­per­a­ture in hot weather are just as im­por­tant to en­gine dura­bil­ity.

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