Dr. Gizmo Automotive Column

"Dr. Gizmo"

By Phil Arendt

No Heat ! 

Question 1
My 2004 Volkswagen Passat with 14,000 miles has no heat blowing from the vents.  Air blows at all speeds but when setting the temperature high only warm air at best blows from the vents.  All the vents respond to the desired position on the controls.

I took the car to a repair shop where a technician found that hot antifreeze goes to the dash but he thinks the core in the dash is blocked so the antifreeze is not flowing through the part.  He tried to clear the blockage by flushing the system but this did not solve the trouble.  Now he says the part in the dash needs replacement, but he does not do these types of repairs on Volkswagens.  He suggests that I take the car to a dealership.

Do you think his diagnosis is correct?  Is it necessary for me to take the vehicle to a dealership?  T.L., email

Answer 1
The fact that he does not do major repairs on VWs is a minor point.  The heating system in your car works on the same basic principles that just about every other vehicle utilizes so his diagnosis likely is on target.  It is likely the heater core is blocked and needs replacement. 

Now that you are about to take the car to another repair shop more than likely when you tell them what was found at the original shop, their technician will likely confirm that indeed the core is blocked before they proceed with the repair.  This requires extensive disassembly of the dash.  Before a technician tackles the task he will want to make sure the trouble is in the heater core before he proceeds with the operation.

As for where to take the car for repair, a dealership shop technician certainly will have all the necessary tools and technical expertise to tackle the job.  Additionally, there are independent repair shops that specialize in this type of work so you might consider awarding the repair to an independent shop but keep in mind price, warranty and experience before making your decision.

Transmission Fails Testing But Operates Fine
Question 2
The check engine light turned on in my 2003 Porsche Boxster S with a 3.2 engine.  I took the car to a shop where a mechanic found computer codes that indicate a problem in the transmission.  The car has 40,000 miles on it and the transmission works just fine.  The technician cleared the codes.  The light was off when he was done.  During a test drive we drove a few miles and the light turned back on.  The technician said that he needed to test the computer again to see if the same code returned.  It did and he suggested the transmission needed replacement.

The transmission operates as good as it did when the car was new.  I don’t beat the car although once in a while I accelerate aggressively.  I don’t race it.  What do you think is wrong with the transmission?  N.L.K., email

Answer 2
You have more experience with the feel, sound and operation of the transmission than the technician.  Since it operates normally I doubt it needs replacement.  More than likely something as simple as a corroded electrical connection needs cleaning.  Consider taking the car to another shop for a second opinion and further diagnosis.

Disagreement Over Diagnosis
Question 3
I own a 2002 Jeep Liberty with a 3.7-liter engine and 125,000 miles.  I purchased the car two years ago when it had 100,000 miles.  It’s in excellent condition.  The trouble is that the service engine soon light turned on. 

I went to a reliable shop.  The technician said there is a code in the computer for a misfire in the third cylinder.  He checked the spark plug and suggested that the trouble is caused by an original spark plug installed at the factory.  He said that the trouble would be resolved by installing new spark plugs.  I did not authorize the work.

When I purchased the vehicle the previous owner gave me copies of all the service records.  The spark plugs were replaced at 60,000 miles.  A friend who knows a lot about cars said that spark plugs easily last 100,000 miles.  Do you think replacing the spark plugs will resolve the trouble or is there another problem?  L.F., email

Answer 3
It’s great that the previous owner supplied copies of repairs and maintenance.  Not all sellers will do that, but it’s a good idea to ask and make your purchase decision accordingly.

As for the spark plugs, certainly there may be troubles such as a failed coil or spark plug boot but according to the factory service schedule the spark plugs in your engine should be replaced every 60,000 miles.  More than likely installation of new plugs that meet or exceed factory specifications will cure the trouble.

Concerned Over Sound Made By Piston Slap  
Question 4
Recently, I purchased a 2006 Subaru Forester with a 2.5-liter 4-cylinder engine from a private party.  The car has 36,000 miles.  The seller provided all the service records.  The car was well maintained.

Since my purchase in the morning when I start the engine for the first time of the day I hear a knocking sound that seems to come from the engine.  I took the car to a dealership to have a technician listen to the engine but it wasn’t making the sound.  He said that it is common for a cold engine to make knocking sounds until it warms up.  He called it “piston slop”.  He said this is not a condition that needs repair and the engine should last the life of the car. 

Does this sound right to you?  T., email

Answer 4

It’s likely the noise you hear is commonly called piston slap.  The conditions you describe are consistent with this condition.  While the sound can be disconcerting it is considered an annoyance and not a symptom of impending engine doom.

The cause of the condition is simple.  When the piston cools down the metal contracts and the piston becomes smaller.  When you start a cold engine, the piston being a little smaller makes a knocking sound until it heats up and the metal expands making the piston larger.  Once it expands the knocking stops.  There is no cure. 

Broken Filter Impairs Transmission
Question 5
Recently, I had a problem with the automatic transmission in my 2005 Jeep Grand Cherokee Laredo with an 8-cylinder engine.  I took the vehicle to my local independent shop where a technician tested the computer and found several codes for internal problems in the transmission.  He also drove it and the transmission acted up for him.  Initially he thought the trouble would be cured by replacing the transmission but he said that the fluid level was proper and did not show any signs of internal problems.

While I was waiting at the shop he dropped the transmission pan and found a broken filter.  He cleaned the pan, replaced the filter and a screen and now the transmission works fine.  He said that he has never seen anything like this before. 

My Laredo has 82,000 miles.  It hasn’t given me any trouble until now.  Nothing has ever been done to the transmission.  Why did the filter break?  Do you think the transmission suffered damage?  I’m afraid the transmission will soon fail.  What do you think?  G.A.J., email

Answer 5
In my many years in this business I have learned that weird things do occur and to expect the unexpected.  I have encountered broken transmission filters.  When a filter breaks it impairs the flow of fluid and the transmission does not operate normally.  Since the factory recommends a transmission fluid service at 60,000 miles the filter likely failed because it provided service beyond its normal service life.

Since the transmission now operates as designed, apparently no harm was done.  Don’t lose any sleep over this incident.  The transmission may last another 100 or 200,000 miles as long as it is serviced again in 60,000 miles or sooner if a technician finds evidence that the fluid is showing signs of excessive wear.

Leaky Gasket Results In Costly Repair
Question 6
I own a 2008 Ford F-350 Super Duty with a 6.4-liter diesel engine.  It has 177,000 miles.  Recently, the radiator coolant tank started bubbling over.  A technician examined the engine and came to the conclusion that it overheated although I never saw any indication on the dash.  He replaced the thermostats but the trouble continued.

Now he says the head gaskets are leaking.  It’s an expensive repair.  Do bubbles in the radiator tank indicate that the head gaskets are leaking or is there another problem? T.D., email

Answer 6
While failed head gaskets could cause the condition, cracked cylinder heads could cause the trouble, too.  Either way the cylinder heads need removal.  Once they are removed a machine shop will do a thorough evaluation.  It is entirely possible the heads need replacement due to cracks and not just the gaskets.  Keep your fingers crossed this is not the case. 
           

Thanks for all of your great questions.  Dr. Gizmo can’t wait to answer more.

Phil Arendt is a columnist, consultant and A.S.E.-Certified Master Technician.  Readers may send questions to Dr. Gizmo at P.O. Box 548, Cary, IL. 60013 or e-mail address drgizmo@drgizmo.ws. ® DR. GIZMO © 1989-2012