10 Car Mysteries Solved: Expert Car Clinic Q&A

PM senior automotive editor Mike Allen tackles readers questions on cars and pickups that won't start, when to change brake fluid and steel vs plastic calipers.

By Mike Allen
September 8, 2009 12:00 AM
The pins on a noid light (used for testing fuel injectors) match up with the pins on your fuel injectors. (Photograph by Dennis Kleiman)

Lights On

My car has become very unreliable. It often won't start. Yet by the time I get it towed to the shop, it's fine. I can't tell if the problem is the ignition or the fuel injection. Is there some easy way to tell if the injection is working?

Tackle this one systematically. If the engine has fuel, spark and compression, it will start. Does the fuel pump work? You should be able to hear it run for a few seconds after turning on the key. Is there spark? Get a spark tester and confirm there is a spark across the gap of the spark plug. Is the injection delivering fuel? You can pull an injector and check that it's spraying, but a simple test of the injection system is called--I kid you not--a noid light. And no, I don't know why it's called a noid light. Anyway, this simple test uses a small bulb mounted in a case. The bulb has contacts that mate the harness to the injector. Unplug an injector, any injector, which probably won't take any tools at all. Plug in the noid light, and prop it up so you can see it from the driver's seat. Crank the engine, and the light should flash. If it does, you've confirmed power to the engine computer and data coming to the ECM from a half-dozen different sensors. Yes, you can do this with a digital multimeter, but it's sometimes hard to back-probe those injector connectors, and it's not a good idea to probe the female pins, because they're easy to damage. The noid light is just a simple, inexpensive go or no-go test.

Oil Spill

My daughter has a 2001 Ford Explorer with 90,000 miles on the clock. It runs great. However, when I changed the oil I found coolant in it--yet the coolant level is full. In my many years on this planet I have never seen this happen. What is going on?

There are three alternatives:

1. Someone is pouring coolant into your oil-filler cap.

2. Coolant is leaking into the oil. And it's probably from a bad head gasket. (Of these two alternatives, I'd bet on the second. As to your claim that the coolant level is still full, it only takes a small amount of coolant in the oil to look like a lot of coolant in the oil.)

3. It's not really coolant, but condensation turning into a mayonnaise-like goo and collecting in the cooler parts of the crankcase, including the inside of the oil-filler cap. This is a problem during extremely cold weather, and in vehicles that are used for urban service and never warmed up for a long enough time to force the water out through the crankcase vent system.

Long-Life Lights

I have a 2005 Chevy Tahoe Z71. The third brake light is out. I went to the auto parts store and they sold me the bulbs. I removed the light assembly from the truck but cannot find any way to open it so I can replace the bulbs. Is there a way to do this? Or, do I need to replace the entire unit? It would seem crazy to replace an $80 part to change a $1.50 bulb, no?

You need to go back to that auto parts store. The CHMSL (Center High Mounted Stop Lamp, if you must know--hey, it's the DOT's terminology, not mine) on your truck is populated with light-emitting diodes (LEDs), not replaceable incandescent bulbs. It's a sealed assembly, and you can't replace the LEDs yourself. If that sounds crazy, just remember that the customary life span of those LEDs is far longer than the life span of your truck. And I doubt that every single one of the dozen or more LEDs soldered into that assembly is fried.

Check the wiring. Check the fuse for the third brake light, which is different from the fuse that controls the brake lights in the car's body. It's a 10-amp fuse labeled "CHMSL" in the fuse panel. By the way, this fuse also feeds the brake-light circuit in the trailer connector, so if you've been towing trailers with funky electrical systems--which is most of them, it seems--it may well be blown.

ABS Anecdote

While replacing a broken wheel stud on my girlfriend's 2005 Chevy Cobalt, I had to unplug the ABS wiring located above the spindle so I could pull out the hub. I plugged the two connector ends together after putting the hub back in place, but now the ABS light on the dash panel is lit. She is sure it wasn't on before I did the work, so I was wondering if a temporary illumination of the light is normal after it is unplugged?

That light would go out on its own if the ABS sensor was working. I'm always skeptical when people tell me that none of the warning lights were on before an (attempted) repair. I always start any diagnosis with a short scan-tool session, downloading trouble codes and browsing for problems--not all of which will make a light come on. Also, I'm curious. What exactly happened to this car that caused the broken wheel stud? Those studs are stout, so anything that could break wheel studs could have inflicted collateral damage in that entire corner of the car. Check the clearance between the sensor and the tone wheel. Try swapping a different sensor in that corner if one of the others will fit. But I'd start by removing the connector, swabbing it out with some electrical contact cleaner and putting it back together.

Properly Mixed

I accidentally poured some windshield-washer fluid into the radiator. My coolant mix is two-thirds water, so will the washer fluid hurt the radiator? Or should the radiator be drained and filled with new coolant?

First off, your mixture is incorrect. The coolant mix should be 50/50 coolant to water, not 33/67. That combination will provide your engine with the proper compromise of good cooling, freeze protection and proper additive concentration to fight corrosion in the cooling system.

Exactly how much windshield-washer fluid did you add, and what kind? Winter-grade washer fluid is 70 percent alcohol, which has a boiling point well below the water or coolant. More than a few ounces in the system could lead to a boilover as you're traveling uphill on some hot day. Summer-grade fluid has less alcohol and is basically just water, a little surfactant and blue dye. If your cooling system is really two-thirds water and a quart or so of alcohol-based washer fluid, you need to flush and refill it with the right stuff.

Next time you remove a cap and it says "use 50/50 mix of coolant and water," take note. They're not telling you how to make a margarita.

You Need This: Pulling the Wires

Sparkplug We've discussed the procedure for removing an old steel spark plug that's installed in an aluminum head before. It ain't easy. Last week I had to change a set of plugs that hadn't been touched for 15 years. The hardest part was actually removing the spark plug wires to access the plugs. The rubber boots had stuck to the porcelain insulator, and refused to let go. Pulling on the wires will just leave the boot and metal cap stuck on the plug. And the rubber boot acts like a Chinese handcuff--pulling harder only tightens its grip. I had to go back into the toolbox and get my special plug-wire pliers. The secret? Grip the boot with these pliers, pull a little and twist a lot. This will break up the adhesion. The small flange on the base of the pliers will lift the boot from the bottom.

Exhaust Plug

A friend of mine took his 3-year-old pickup in for an oil change. The mechanic talked him into a $52 fuel-injector cleaning. Within two weeks, his catalytic converter plugged up to the point that his engine would barely run. His dealer confirmed that the problem was a plugged-up converter and changed it under warranty. I wonder how many others have gone through the same experience. In your opinion, is there any problem using injector-cleaning additives?

I have to think the injection-cleaning procedure was not followed properly, damaging the converter. Your friend is lucky the dealer fixed it for free.

I don't recommend routine injector cleaning for vehicles that are running properly. There are two classes of injector-cleaning machines: on-car and off-car. The on-car style requires the mechanic to clamp off fuel lines and isolate the fuel rail. Then a concentrated cleaning solution is pumped in and the car is allowed to idle for 20 minutes or so, burning the cleaning solution instead of gasoline. Not following the injector-cleaning-machine manufacturer's directions can make the engine run too rich or misfire, and literally slag down the inside of the catalytic converter.

A more expensive way to clean injectors involves removing them from the manifold and installing them in a device that recirculates a powerful solvent through the injectors as they sit inside a clear chamber where you can watch the spray pattern and measure the flow. This procedure can't damage the cat, because the car is likely on the other side of the shop while the injector work is done. Any injector that has a low flow rate or a poor spray pattern will have to be replaced.

Most cars don't need periodic injection cleaning. An occasional bottle of injector cleaner or an occasional tankful of Top Tier gasoline (which has more detergents than the EPA requires) should do the job.

On the other hand, if your driveability or fuel economy has dropped off, and the problem doesn't seem obvious, a session on one of these machines might help. At least if it's properly done.

Plastic Pistons

I need to replace the rear brake pads and caliper on my 1999 Jeep Grand Cherokee. The counter guy at the local shop asked me if I wanted the part to be phenolic or stainless steel. I called my Jeep specialist and he didn't know there was a choice?and wasn't familiar with the term ?phenolic.? Have you done comparisons between the reliability of phenolic versus stainless steel?

Most brake calipers have traditionally used hydraulic pistons made of hard-chrome plated steel. Steel is a good match for the cast-steel caliper. Neglected vehicles, and those operated in wet, salty environments like the seashore or the Midwest, can have problems with the corrosion of the steel as well as with flaking, pitting chrome. Eventually, the corrosion interferes with the movement of the piston in the caliper bore. Then it's time for a rebuild.

A few years back, some car manufacturers switched over to pistons made of phenolic resin?i.e., plastic?to reduce corrosion and weight. As a side benefit, the pistons transmitted less heat from the friction material in the pads to the brake fluid. And that reduced fluid breakdown.

Some mechanics didn't like the plastic pistons, because they couldn't really be reused. For many vehicles, you have the choice of replacing a caliper with a rebuilt unit that uses the original phenolic, or steel. I actually prefer the lighter plastic ones..PM

Risen From the Dead

My pickup has failed to start on several occasions after sitting overnight. In the morning, the ignition is dead and there is no electrical power at all (interior lights do not work). Then I'lI hook up the battery charger and immediately the interior lights come on and the truck will start. It's obviously not the battery as I have purchased a new one and still have the same problem. I've taken it to the GMC dealer and they can't find anything wrong.

It's almost certainly a bad connection to the battery at the posts or the cables. No interior lights or dash lights when the key is turned on means either a completely dead battery, which would take many hours to charge, or simply an open connection.

The physical act of attaching the battery charger leads is disturbing the battery connections just enough to make the connection, and off you go.

I'm the kind of guy that will leave a meter on the front seat for the next non-start. That will allow me to chase the voltage drop across every connection anywhere near the battery until I find the one that reads 12 volts across the connection, pinpointing the problem. Other folks who may be less curious or less obsessive (you know who you are) will simply clean and tighten all the battery cables.

Don't forget, the problem is just as likely to be the ground side as it is the positive cable.

Saab Story

I have a 2001 Saab that was recently in a front-end accident. The airbags deployed, but the engine and everything except for the radiator and fan came out unscathed. Even though the damage is mostly cosmetic, our insurance company is going to total the car, because we received a quote of over $4000 to replace the airbags, along with the sensors and computer?and the entire dashboard?even though I haven't found any damage to it. Is this normal?

Yes. Most car manufacturers recommend replacing not only the airbags themselves, but the entire airbag system, including the airbag controller, the sensors and all the wiring harness, as well as the dashboard and its underpinnings, if the airbags deploy. Four grand is typical. (Ouch!) The insurance companies are concerned about the possibility of future lawsuits if a repaired car is in a second accident and for some reason the airbags don't deploy. So they prefer to total the car and wash their hands of the whole mess.

No surprise, many of these cars are eventually repaired and sold, although they generally must carry a salvage title. Body shops buy these cars from the adjuster, and keep them around to work on in slow weeks, eventually selling them to private individuals or sending them off to auction.

You might try to keep the title and possession of this car yourself and have it repaired. A good shop should be able to make the airbag system as safe as new, by replacing any parts actually damaged with new or salvaged parts. I would specify new, rather than used, airbags.


I have a late-model Chevy Silverado that is used as a daily driver?no trailering or heavy loads. My dealer's maintenance pamphlet suggests changing the brake fluid every 30,000 miles. The dealer claims the brake fluid can absorb moisture and become very hot, thus justifying a change. My vehicle has ABS and it seems to me this could cause more harm then good.

GM agrees with you that brake fluid never needs to be replaced. They seem to be the only manufacturer that doesn't recommend periodic flushing of old fluid. The issue, as you suggest, is water contamination, which lowers the boiling point of the contaminated fluid to a level where hot brakes might make it boil, reducing brake effectiveness. There are electrical testers and disposable strips to check the moisture content of brake fluid.

But there's a second issue. The brake-bleeder bolts in the calipers or wheel cylinders will eventually freeze in their threads if they are never loosened. If it ever becomes necessary to bleed the system, they can then be difficult to remove. I recommend semiannual flushing of old brake fluid. If you watch, and see how the old fluid looks when it comes out (it will look like squid ink, not clear, like new fluid), you'll probably agree.

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