CORRODING CATS - CAUSES AND CURES


This article by J.D. Palmer appeared in the May 1986 issue of the Ontario Jaguar
J.D. Palmer
London, Ontario
Canada
My first encounter with corroding Jags came in 1961 when I snapped a moderately rusted MK IX to use in an automotive corrosion talk - as an illustration that corrosion affects the mighty as well as the Mini. At the time I was running a winter test to determine whether the addition of a phosphate inhibitor to highway deicing salt would reduce the corrosive effect of the salt. It didn't.
Bitten by the bug (flea?) I got my first Jag - a '61 3.4 Sedan manual LHD with overdrive. Corrosion soon struck when the Servo vacuum reservoir corroded through with loud hissing sounds. The reservoir isn't needed when the car is running and by-passing worked until the car stalled on a ramp where the hand brake was quickly needed. A epoxy-fibreglass patch on a well- abraded surface corrected the problem.
Corrosion struck again on a trip to Boston. The fuel pump was loosing suction intermittenly and a new pump bussed in overnight to a Massachusetts motel didn't solve the problem. The drive through the hills consisted on frantic down-hill runs to build up enough momentum to get up the other side much to the annoyance of other drivers. The cause was a corroded fuel line where it passed through grommet-temporarily patched with Plumber's Epoxy.
Beleagured by a clumsy wife learning to drive and unable to handle either the MKII or my Sunbeam Alpine, I traded them both for an Alpine wagon - a real dinky little car. The same wife cost me my second Jag.
The next cat, a '68 340, was a steal from a Pontiac dealer who didn't know what to do with it. It was used on business and one day while waiting for a client on a job site, I noticed the blister typical of underbody corrosion - right in the middle of the right front door panel! Removal of the trim casing showed that someone had stuck a piece of foam rubber behind the pivot of the window winding linkage - presumabley to keep it from rattling. The open cell foam held the moisture nicely and knocked a 1/2" hole in the panel. I caught the left side before it perforated.
The 340 went when, as part of a business tax manoeuvre, transferred it to my wife who promptly sold it! She went shortly after and I was finally in a position to enjoy Jags unencumbered. Subsequent ladies were quite aware that I came complete with Jag and planned on remaining so.
A well treated '74 XJ6 (Automatic) came next. It had been corrosion- proofed (Ming?) and was in good condition, but in the last few years a few body corrosion problems have developed, and this car illustrates Jag corrosion problems in particular and auto corrosion in general. My recent acquisition - a partly restored '61 MKII again, has few visible corrosion problems now that the rad has been recored.
The deicing salt inhibitor test, I previously mentioned, was initiated in a period when highway deicing salt use was escalating phenomenally and car owners were screaming loudly. Several U.S. cities including Rochester, N.Y. had tried inhibitors added to the salt but no proper scientific testing had been carried out. I was commissioned to design, build, and operate a test track where the relative corrosion rates of unsalted, salted, and inhibited road conditions could be determined. A carousel type of rig was used with steel coupons enclosed in fenders were wheeled around with one rig unsalted,one salted, and one exposed to inhibited salt. The use of salt roughly doubled the corrosion rate but the inhibitor (a polyphosphate) was not effective in reducing the corrosion.

Deicing salt consumption continued to escalate and a few years later Cargill Inc. came up with a promising non-polluting inhibitor, and I was retained to direct a cooperative test sponsored by The American Public Works Association, Cargill, Ford, and the Salt Institute. The test was run year-round including three winters using nine Ford Falcons. Three were driven daily in an unsalted suburban area, three in a salted urban area, and three in an urban area where the inhibitor was added to the salt. As well as studying the effect of the inhibitor, we looked at the seasonal corrosion patterns, the effect of industrial pollutants, and the effectiveness of various paint and trim system preventive measures - The cars were completely dissected after the third winter and evaluated by Ford staff. There was little difference between the inhibited and uninhibited cars and the inhibited salt was not placed on the market. Other evaluation tools showed that when the inhibited salt was used at least twice a week, significant benefits did result. Undercutting at paint chips was reduced and some trim components were benefited.

The time of year that a car was first exposed to a salted environment was found to be important. A car put on the road in the spring after salt application has ceased will form semi-protective corrosion products before the next winter sets in and will suffer less corrosion after a years service than a car put on the road in the fall or winter. This effect is less important in maritime areas where salt exposure occurs year round.
The report recommended that the best use for an inhibitor was in a car wash with an underbody spray. This was further researched in England and found effective but has never been picked up by the commercial car wash industry. The only reason I can find is that an underbody spray tends to stall cars and presents a vehicle handling problem.

All automobile components and systems are subject to corrosion; under- body, under-trim, exhaust, brakes, fuel and cooling. All have their own charcteristics and I'll discuss each separately. But first, why do cars corrode?

Underbody corrosion is caused by what is called "poultice" and "sheltered" corrosion mechanisms. Poultice corrosion occurs when a lump of road soil forms on a steel surface, retaining moisture, and causing corrosion around the outside of the lump. The corrosion rate is increased if the moisture is contaminated by salt, exhaust condensates, acid pollutants, and the many other corrosive agents that can be found on the road. Sheltered corrosion occurs when a surface does not dry out,quickly and remains wet for a high percent of the time. Salt contaminated surfaces corrode during cold weather because the steel surface is wet when it would normally be dry.
The corrosion rate is temperature dependent, doubling for every 18 degree F increase. The APWA test showed that the highest annual corrosion rates occurred during the spring when the salt-contaminated surfaces started to warm up. Similarly, a dark-colored car absorbs more radiant energy than a light-colored car and will corrode at a higher rate. other testing has shown that underbody corrosion tends to be greater on the curb side and in the rear because of the more intense slush spray. Interior corrosion tends to be greater on the driver's side because of tracked-in salty slush in the winter.

Geographically, deicing salt corrosion is common to the snow belt but is higher in the warmer wetter east and mid-west than in the cold dry central area. Salt induced corrosion is found on the warm humid sea coasts with Houston and Miami representing very corrosive conditions.

Under-Trim corrosion is caused by corrosive moisture retained in the crevice between the trim and the body. The paint is often damaged during trim installation, causing localized corrosion of the bare steel. The attack can be accelerated by galvanic effects - a condition where, for example, stainless steel will accelerate the corrosion rate of mild steel if the two are in electrical contact. The same action causes aluminum to corrode in contact with steel or copper and steel to corrode in contact with copper or brass.
Exhaust System components are affected by three different corrosion mechanisms. The internal surfaces are corroded by acidic exhaust gas condensates which tend to form in the lower, cooler points in the system. This effect is worse in colder areas and under stop-and-start driving conditions - to work and back or on shopping trips. The effects are lowest on extended long-distance travel.
The outside surfaces are corroded by wet road soils when the metal is cool - again worse under stop and start conditions. When the surface is hot, high temperature oxidation occurs usually at a lower rate than under wet cold conditions.
BRAKE SYSTEM hydraulic tubing can be corroded by the same mechanisms that cause underbody corrosion and is particularly affected where the tubing contacts the body or passes through sections - usually through a rubber grommet which forms a crevice.
The corrosive action can be accelerated by fretting which removes the somewhat protective corrosion product exposing fresh metal to the corrodents.

Cooling Systems may contain cast iron, brass, copper, aluminum, and lead/tin solders, and galvanic corrosion will occur if the coolant contains corrodents. The presence of oxygen in the coolant will increase attack - a system that is regularly topped-up with fresh water will be more corrosive than a tight leak-free system. Commercial coolants contain corrosion inhibitors but these deteriorate with time and temperature and the coolant itself can decompose to form corrosive acids if left unchanged. Combustion product leakage into the coolant will also introduce acidic corrodents.

CORROSION CONTROL is a joint effort between the car manufacturer and the owner. Corrosion problems are designed-in by the manufacturer and his mistakes must be corrected by an owner who has little opportunity to find the mistakes and limited opportunity to correct them.
Manufacturers initiate the problem by their mechanical design and material selection. The initial design is a compromise between safety/performance considerations, manufacturing costs, and marketability. From a corrosion standpoint, the manufacturer selects a design criterion - say five years to first underbody perforation. Typically, unprotected 20 gauge auto steel will perforate within three years. Protective measures can be precisely engineered to give another one, two, or three year's of life.
In Canada, the "Federal/Provincial Anti-Corrosion Code for Motor Vehicles" introduced a 3 year perforation-free requirement for 1978, increasing to 5 years in 1981. Unfortunately, in 1978 Worth American manufacturers were planning a 5 year life and the governments, without competent advice, allowed them to postpone the improvements for another three years. Currently, a five year life to first perforation is the common standard,Underbody and sheet metal design combines structural considerations with aesthetic factors. The unit-body design relies on structural contributions from the sheet metal and safety considerations make protection against corrosion necessary. The recent trend to weight-saving high strength- low alloy steels has increased this requirement since these steels actually corrode more rapidly than ordinary body steel under poultice and crevice conditions. Reinforcing creates many crevices, nook, and crannies which may be open to road splash or precipitation run-down but which drain and dry poorly. Enclosed areas such as-rocker panels and doors may be equipped with drain holes but these may not fully drain the area and may be easily plugged.
The manufacturer must then identify these locations and apply some form of protective coating (paint?) to extend the service life. Protection of these areas was much improved by Ford's development of electrocoating where the body is immersed in the paint and the film is deposited by an electrical charge. This process can be engineered to provide uniform paint thickness on edges and in crevices and is now the standard process in the automotive industry. Some locations are not suited to this type of coating and the "Ziebart" approach may be used, where protective materials are sprayed into sections after the car is assembled.
Zinc-coated steel use has greatly increased with both galvanized and zinc-rich coatings used extensively. The weight or thickness of the zinc coating can be adjusted to give a specific service life. Galvanizing can adversely affect the performance of finishes, and special primers and pre-treatment may be needed. various primers may be used to both improve finish adhesion and to control undercutting at paint defects.
Current top-side finishes are of high quality, often consisting of a base color-coat followed by a final clear coat which provides chemical resistance, ultra-violet resistance and protection against physical damage. On areas where mechanical damage is more common, a high-build vinyl or urethane top-coat may be used and is recommended for refinish project, particularly if gravel roads are regularly travelled.
Increasingly, plastic body parts are being used, offering much improved corrosion resistance but reduced resistance to the discoloration and hardening caused by ultra-violet radiation.
Trim and Bright Metal applications often involve stainless steels and anodized aluminum. Performance can be excellent but care must be used in the use of abrasive cleaners as both materials rely on a surface oxide film for their resistance to corrosion. Aluminum coatings on the- contact side of stainless steel mouldings have been effective in reducing crevice and galvanic corrosion effects, as has the use of improved synthetics to prevent electrical contact between the trim and the sheet metal. Stick-on trim is common but the adhesives used have not always been durable.
Modern chrome plating for automobile service actually consists of two layers of nickle with a chromium. top-coat for improved appearance and durability. The chromium may be applied with a micro-cracked surface to spread the deterioration uniformly over the surface.
Improved exhaust system life has resulted from the increased use of galvanized and aluminized steel. Stainless steels would give further improvements but the relatively inexpensive replacement market situation makes the increased cost difficult to justify. Modern mufflers usually last about three years and most new cars are traded within this period, leaving the replacement up to the used car buyer. Catalytic converters operate under severe conditions and are filled with expensive catalysts, and more resistant alloys can be justified for this service.
Cooling system - components are protected against corrosion by blended inhibitors added to commercial ethylene glycol. in general, brass, copper, and cast iron are the most durable with aluminum subject to cavitation pitting, velocity corrosion, pitting due to copper deposition, and galvanic attack. Inhibitor depletion can affect some materials more than others. The inhibitor contains different constituents which are added to control specific types of corrosion and some may deteriorate more rapidly than others. Surveys have shown that around 20% of one-year old cars have appreciable cooling system corrosion and that most cars coolant concentration are lower than the 50-70% mixture recommended for low temperatures and severe driving conditions. In this case, all the manufacturer, can do is recommend coolant replacement frequencies in keeping with his materials and operating conditions.
BRAKE lines are now almost always Terne coated (lead-tin alloy), galvanized, aluminized or stainless steel although the latter material has a tendency to pit and crack. Failures continue to result from grommeted fittings and from corrosion-abrasion where the lines are in loose contact with another component.
What does Jaguar do? Jaguar dealers in Toronto and London, Ontario could give only limited information on their corrosion prevention measures. They use a type of wax-base undercoating for underbody parts. I looked at a 1986 XJ6 being dealer prepared and found that there was a heavy overspray of some form of mastic on a floor panel and most of the rocker panel drain holes were plugged with a black material. It is unlikely that a dealer would check and clear all drains. Jaguar still uses open cell foam rubber beneath the floor mats, even though closed cell silicone foams are readily available. I was told that high-build materials are used on below-door level modesty panels but the XJ6 I examined did not appear to have this type of resilient top-coat.
Paint finishes remain a multi-coat baked acrylic system although they are apparently looking at the base-coat/clear coat approach. Jaguar does not recommend any of the post-assembly corrosion preventive treatments. Mufflers, resonators, converters and exhaust pipes are stainless steel but the tail pipes are mild steel.
Where do Jags Corrode? : Using the MKII series as a guide, attention should be focused on major underframe structural components with particular emphasis on the left and right side member assemblies. The "U" shaped main members will corrode from the inside out. The front and rear floor panel assemblies are next in importance, corroding on both the inside (wet floors) and from the outside - particularly at joints where open crevices exist.
All the remaining underframe components and all body panels below the "belt line" (door handle level) are subject to insideout attack. Above the belt line, in some areas where high humidity is common, overnight condensation can cause severe internal corrosion of the roof panel. All under-fender nooks and crannies where soils can be retained are trouble spots including the headlamp and sidelamp sockets.
Brake and fuel lines will corrode at grommetted and contact points and the upper surface of the fuel tank is sheltered and subject to serious attack.

What Can You Do?

Starting with a new car or a major restoration, you must consider some form of post-assembly corrosion-proofing. Most applicators will not warrant used cars but some have treatments designed for used vehicles. In either case, it is necessary to drill holes to get access to the many closed off (but not sealed) box sections and crevices. A protective coating must be sprayed in with 360' coverage over the length of the section. The coating material must have low viscosity and good wetting ability and must be resistant to water and chloride and acid solutions. The paraffin-based hydrocarbon materials typified by the Ziebart material appear best suited for this application.
To properly protect a vehicle, the applicator must carefully analyse the manufacturer's assembly drawings and determine how each particular section can be reached. Success is then dependent on how thoroughly the person doing the application follows the procedure. A CONSUMERS GUIDE TO BUYING AUTOMOBILE RUSTPROOFING, published by the Maine Attorney General's office (Augusta, Maine 04333) is the best guide I've seen. It would also assist those wanting to apply protection during a ground-up restoration.
During a restoration, new parts may be protected before installation but this is limited where welding is required. An alternative would be a carefully selected post-assembly treatment. Sandblasting and application of a high solids zinc-rich inorganic coating primer followed by an epoxy or urethane top-coat would be a premium treatment. Epoxy coatings requiring less rigid surface preparation are also available. Zinc-chromate primers followed by epoxy top-coats are also a very resistant system. Galvanized replacement parts may also be available and are a good choice although finishing requires special treatmeats.
Cleanliness is next to godliness where body corrosion control is concerned. The following section from the Haynes Owners Workshop Manual covers this point nicely.
  1. " The condition of the bodywork is of considerable importance as it is on the visual condition of this that the resale value of the car will mainly depend. It is much more difficult, and costly, to repair neglected bodywork than it is to renew mechanical assemblies. Attention to the hidden portions of the body such as the wheel arches and the underframe is as important, if not more so, than periodic cleaning and polishing of the paintwork.
  2. At frequent intervals, especially during the winter months, remove the rear wheel covers, raise the car and thoroughly hose down underneath to remove all mud and road dirt from the wheel arches and projections on the underframe. Pay particular attention to the front part of the front wheel arches, the valance beneath the radiator, inside as well as the outside of the four jacking points, and do make sure that the rubber plugs are fitted at these points, the space between the petrol tank and the body and the wheel covers themselves. These, amongst others, are all places where mud will collect and cause corrosion especially if impregnated with salt.
  3. The insides of the doors are fairly well protected but nevertheless take off the door panels at least once a year, to make sure that the drain holes are clear and that there is no corrosion.
  4. once a year, preferably in the summer, is advisable to have the underside of the body steam cleaned. This will remove all traces of dirt and oil so that the underside can be examined for rust, damaged pipes or electrical wiring.
  5. The wheel arches should be given particular attention to ensure that the undersealing has not been damaged by stones thrown up from the wheels. If damage is found, clean down to the bare metal using a wire brush and then paint on a rust inhibitor or, if preferred, red lead and finally recover the area with underseal. "
Use a screwdriver to clear all door and rocker panel drain holes and reverse flush through the holes. Remove the rubber plugs in the jacking slots and flush - in all cases until the water runs out clear.
Car washes are a debatable subject. From an underbody corrosion control viewpoint they are questionable. Few have effective underbody sprays and most recirculate their wash water, resulting in a salt solution being driven into crevices in deicing salt areas. A wash with a good underbody spray using clean water would be a worthwhile investment. In any event, a thorough spring and fall cleaning is the minimum requirement. Regular winter cleaning-would be a great help, as would summer cleaning if you drive on gravel roads where calcium chloride is applied for dust control.
Interior floor panel corrosion can be controlled by first removing any open cell foam rubber and cleaning the floor and applying a coat of a fast-drying bituminous mastic. If desired the rubber strips in the floor corrugations can be replaced with a closed cell silicone rubber contact-cemented in place. The floor undermat should be checked regularly and removed and dried if moist Similarly carpetting will rot if left wet and should be dried out with a hot air blower.
The paintwork requires regular cleaning and waxing. Again many Fine car owners prefer hand-washing to automatic washes. Cleaners and waxes are heavily promoted. The July '81 issue of Consumer Reports rated 35 polishes, finding considerable variation in performance on both dull and shiny surfaces. Protect It #3 and Rain Dance paste were top-rated and I have been very satisfied with Rain Dance. Re-polishing when water stops beading is recommended - after about eight washings. Retouching of stone chips and scratches with either paint or clear lacquer is desirable. Brightwork and trim cleaning requirements vary. Aluminum and stainless steel cleaners should be non-abrasive while chrome plating can be cleaned with household or automotive abrasive cleaners. Cleaning trim next to painted surfaces must be carefully done to avoid paint damage. A used tooth brush is useful for wire wheels and similar complex surfaces.

Cooling systems require regular attention. Leaks require regular topping up - detrimental to the system so tighten up hose clamps regularly. Fill and top-up with no less than 50% coolant - 70% for severe driving conditions. Change the coolant at least annually - semi- annually for severe conditions and flush the system at the first sign of overheating.

Brake and fuel lines will benefit from thorough underbody cleaning but visible grommeted points should be regularly checked and replaced if localized corrosion is evident. If this is a chronic problem, a plastic tubing sleeve can be fitted over the affected area.
Garaging is a problem - particularly in the snow belt. The worst situation is a warm, poorly ventilated garage. A clean car left outside in cold weather will not corrode. A dirty Car will corrode less if cold. If you drive your car from a warm or even sheltered garage to a similar parking garage it will suffer accelerated corrosion.. Reinforced concrete garages across the world are themselves suffering severe corrosion in the snow-belt. if, like many, you lay up your precious cat for the winter, clean it thoroughly above and below and find a cold dry place. outside is OK if you have thoroughly waxed and polished before lay-up. Lay-up fuel system conditioners prevent corrosion and fuel additive decomposition and are beat added to a full tank and run-in for a brief period. Periodic warmups reduce the possibility of localized corrosion in the cylinders caused by acidic condensation, as will an oil change just before layup.
Electrical Components and particularly the terminals can be corroded by salt-contaminated moisture. The first step in diagnosing an electrical defect is to check and clean all terminal points, grounds, etc. Chronic problem components can be bagged with plastic and including a small packet of silica gel dessicant in a panty hose foot will reduce moisture levels. Commercial vapour phase corrosion inhibitors are available but not easily obtained by the average person.
Vaseline, Glyptal, and other commercial electrical coatings can be easily applied to terminal (cleaned) or used to seal off semi-enclosed terminal boxes. Commercial drying agents are useful and a hot-air blower is always handy.
In the operation of any vehicle, and particularly a valuable classic or antique, corrosion control is as important as any other consideration. For those interested in more detailed study, automobile corrosion publications are available from the following organizations;
National Association of Corrosion Engineers
Box 218340 Houston, TX
77218

Society of Automotive Engineers
400 Commonwealth Drive
Warrendale, PA 15096

In any event, Clean and Dry is Best for any Cat-feline or vehicle.
Sept 12, 2011 by Webmaster