Stop!  Leak!

One of the most common “shade-tree fixes” we see in the shop is the use of stop-leak products.  They make ‘em for lots of different things, like cooling system stop-leak, power-steering system stop-leak, and so on.

Most of these products fall into one of two categories – stuff that clogs things up, and stuff that makes rubber seals swell up.  Some products combine the two.

Stuff that clogs things up is what we usually see in cooling systems.  The problem with stuff that clogs things up is that it… clogs things up!  It doesn’t discriminate between a leak and a coolant passage.  Sometimes it clogs things up so well that we have to replace things we wouldn’t have had to replace otherwise.  Sometimes it clogs things up so well that we have to flush the system out several times, or take things apart to clean them out.  Another type of stuff that clogs things up is a thicker version of whatever fluid is leaking – the thicker, or more viscous, fluid won’t leak out as fast.  It also doesn’t do as good a job doing the job it’s supposed to do – if ya follow me.  For example, a more viscous engine oil doesn’t do as good a job lubricating the engine because it takes longer to get where it needs to go.  This is a big deal, partly because most engine wear occurs on start-up.  If the oil takes a few seconds longer to make its way around the engine, the wear will be much worse. 

Stuff that makes seals swell is made for engines, power steering systems, transmissions – anything that has oil in it and rubber seals to keep it there.  Sometimes these seals wear or harden and leak.  Some products sold to solve leakage problems contain a chemical that makes these seals soften and swell.  These may be an acceptable short-term solution in a very few cases; by short-term I mean a month or two at the most.  I’ve done some experimenting with these products on my own vehicles.  The seals can swell so much that they are at risk of tearing out completely, resulting in catastrophic failure – forcing you to either park the vehicle or make the repair immediately.  In the best possible outcome, the seals swell to seal, then become so floppy or soft that they fail to seal yet again in short order.  It’s probably better just to deal with the leak (protect the driveway and keep the fluid topped up) and save your allowance to have the offending seal replaced.  Here’s another big problem - the seal swelling chemical doesn’t know which seals are leaking, and which ones are in good shape – so you end up replacing more seals than you would have if you’d just done the repair in the first place.  And here’s a word to the wise – many of the recently popular “high mileage” engine oils have seal swelling chemicals in them.

Thanks for your time!  Let me know it there’s a topic you’d like me to write about.

Dave

DOC Auto

The Facts About Nitrogen Inflation

In the last couple of years, inflating tires with nitrogen has gotten a lot of press.  Much of the hoopla is based on misinformation, so here’s the real story.

Nitrogen has been used in aircraft tires for a long time, for one main reason – it doesn’t support combustion, as air at the altitudes we live at does (because of the oxygen content).  Airplanes often operate at altitudes at which the air is much less dense than it is at ground level – that’s why they have those little oxygen masks that fall out of the overhead panel.  If something bad happens that creates a lot of heat in the area of an airplane tire, the heat could cause the tire to fail, releasing whatever gas is in it.  If that gas supports combustion, a fire could result.  A secondary benefit of nitrogen in airplane tires is that the bottled or generated gas they use is very dry compared to atmospheric air.  Moisture in a plane’s tire could condense, puddle, and freeze, leading to an out-of-balance tire when it lands.  This really is just a secondary consideration, because compressed air can easily be dried with equipment that already exists.  If you’re worried about the air in your tires supporting combustion, when your car is already driving around in air (your car is probably powered by an internal combustion engine, using atmospheric air), nitrogen inflation is for you.

One of the benefits claimed for nitrogen inflation is that nitrogen molecules are larger than oxygen molecules, so the theory is that it’ll leak out of your tires more slowly.  Well, air is almost 80% nitrogen.  Combine that with the fact that without special equipment that no shop has, it’s impossible to completely purge the air out of a tire when nitrogen-inflating it, and this theoretical advantage disappears – into thin air.  I read about a test in which 50 tires were inflated with air, and 50 were inflated with nitrogen.  A year later, the researchers checked the inflation pressures of all 100 tires, and found no statistical difference between the two groups.

Some people claim that their car rides better with nitrogen in the tires instead of air; I guess that 20% oxygen is pretty stiff.  I’m not going to dignify that absurd claim with further response.

Another “benefit” of nitrogen is less chance of corrosion of the wheel, tire and TPMS sensor.  Well, isn’t the outside of the wheel and tire rolling around in air??  Sounds dangerous!  Other claims, such as better fuel mileage, are equally silly.  Bottom line – if you want to partially fill your tires with slightly less oxygen and slightly more nitrogen, knock yourself out.  It does no harm.  Just so you know the facts.

Thanks for your time!

Dave

DOC Auto

They should have named it the “Check and Repair Engine” light!

Tonight’s bedtime story is about a wicked, nasty little fellow, known to all as the Check Engine light.  Now, you’d think that  a light would be good - illuminating stuff and helping folks out.  But not the Check Engine light!  This miscreant spent his days in a decidedly un-illuminating way, spreading misinformation, hiding correct information, and generally causing confusion and chaos throughout the land.

There are lots of misconceptions about the Check Engine light (also called the CEL, which is what I’m going to call it from now on ‘cause it’s easier to type) that we run into at the shop.  I’m just going to quickly touch on a few of them.  The CEL - sometimes also called a “MIL”, for Malfunction Indicator Light (not Mother In Law!) - indicates that the car’s computer has detected a malfunction, and has stored one or more codes related to the malfunction.

One thing we commonly encounter is the belief that the code or codes tell you what’s wrong with the car.  This is not correct!  OBD II (which stands for On Board Diagnostics, Second Generation) codes are nothing more than a symptom.  The folks who built your car have written diagnostic procedures for all the different codes. One of the first steps a good technician takes is to refer to his diagnostic information system to look up the procedure(s) for the code or codes in the car he’s working on.  It’s a common occurrence for someone to swing by one of the big chain auto parts stores to get the code read (usually with a code-reader, not a true scanner).  The parts dude then sells the hapless motorist a part.  Hapless motorist then happily skips off to install the part at home.  Imagine his chagrin when the light comes back on a few miles down the road!  This is because the cause of the problem was never diagnosed – just guessed at.

I mentioned that there’s a difference between a code-reader and a true scanner.  Actually, there are many differences – thousands of them if you’re paying for one!  The scanners we use at the shop have many diagnostic functions in addition to the ability to read OBD codes.  They typically have bi-directional capabilities as well as data-stream features, component tests, misfire monitors, diagnostic databases, and many other powerful tools.  Some have four-channel lab scopes and multimeters built in as well.  These capabilities make diagnosing complex problems possible, where a simple code-reader would leave a technician in the dark.

Sometimes, the cause of an illuminated CEL is not really a big deal in terms of the actual operation of the car.  For example, let’s say your gas cap is not making a good seal against the filler neck.  This can trigger an evaporative emissions leak code.  The car will run fine with this leak, so some people will be inclined to just ignore it.  This is one of my pet peeves (I have an entire menagerie of them!)  Sure, the small gas cap leak is not a big deal, but you only have one light!  If something more serious happens, the light’s already on, so you won’t know about it.  Bad stuff can happen as a result.  Another reason that ignoring the light is a bad idea is that many minor faults can increase the workload on other components that are trying to compensate.  But ultimately, I prefer to repair all problems that cause the CEL to come on because it’s the right way to do things.

The CEL tells us that the computer has detected a malfunction – nothing else.  At the end of the day, maybe the poor Check Engine light was just misunderstood…

Thanks for your time!

Dave

DOC Auto

"My ____ fluid needs changing??"

It's a perennial mystery to me that almost every person in the world understands the need to change a car's engine oil from time to time, yet when I tell someone that I recommend changing almost any other fluid, I get a blank stare (or its telephonic equivalent).  The blank stare is sometimes followed by a comment, such as "Well, I never changed that before!"

To me, it stands to reason that all automotive fluids have finite life spans.  A couple of factors play into why a lot of drivers, especially older drivers, "never changed that before."

First, modern cars run much,much longer than ever before.  When I started working on cars in the late 1970s (!), most cars were junked by about 100,000 miles.  So if, say, the gear oil wore out at 60,000 miles, did it make sense to change it if the car was going to be scrapped in a couple of years - or less?  In many cases, no.  In fact, odometers in those days usually only had five digits!  Today, though, almost any decent car will easily go over 250,000 miles without any catastrophic failures of major components.

Another big factor is heat.  Today's cars run much hotter than the old dinosaurs did.  One of the reasons for this is efficiency.  When engines are run cold, they use more fuel.  Computerized engine management systems allow engines to run more efficiently without a meltdown.  Another contributor is the compactness of modern cars.  Everything is packed tighter, so lots of stuff doesn't have much air space around it to help keep it cool.  Heat accelerates the rate at which fluids deteriorate.

A third factor is complexity.  Many modern systems are much more sensitive to fluid condition than they used to be.  An example is brake fluid.  Modern cars have anti-lock braking systems that have little passages and valves in them that don't like gummy, gritty fluid.

The last factor I'll mention also relates to modern automotive technology.  Cars today are made out of many more kinds of materials than old cars.  Different kinds of plastics, aluminum, steel, cast iron, copper, rubber, etcetera, go into cars today.  All those different materials place more demands on the fluids that come into contact with them.

When I feel ambitious, I'll write about individual fluids, what happens to them over time, and what that means to you.

Thanks for your time!

Dave  

We meet some interesting people here at DOC Auto!

One of the fun things about working at DOC Auto is the opportunity we have to meet interesting people and talk about the cool things they’re doing. 

Alia and Travis Reese are long-time DOC Auto customers.  Travis is a Marine whose job frequently sends him on overseas deployments.  Alia began using scrapbooks with photos of Travis to keep him involved in the day-to-day conversations of their two young children.  She realized that other Marine families could benefit from her idea, so she’s written and published two books, American Hero Books: My Daddy is a Marine and American Hero Books: My Mommy is a Marine, with places to insert photos of Daddy or Mommy.  She’ll be coming out with American Hero Books for the other branches soon.  Check them out at americanherobooks.com.  You can look at and fondle the books in person here at the shop.  Great idea, Alia!