The greatest auto repair myths

Is it just me? I constantly hear certain automotive repair myths that just are not true. They send people off to do work that will cost money and time and never produce a successful result.


1 Replacing the stock 190 degree thermostat with a 160 degree thermostat to try to fix an over heating engine. This is like turning the thermostat on your AC down to 60 when it already can’t bring your house down to 78.

What bugs you?

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Yup, that’s a good one!

With all the computer controls now, many mechanics have zero ability to troubleshoot. They just start replacing modules at your cost, and if you are lucky the 2nd one fixes it.

I just put over $600.00 worth of new parts on my Miata, VVT actuator, Up stream O2 sensor, Down Stream O2 sensor, both Coil packs, Spark plug wires and not to clear codes new spark plugs, Oil change and a new valve cover gasket. Each of the first 4 parts cleared a code, then went for a drive, no codes on the way out, but half a block out it started missing. got a code for Cylinder #3 misfiring. It took the coil packs and wires to clear that code.
Now runs like a champ again. It scares me how much it would have cost to have a shop take care of all that. Mean while both old Cougars are running like tops.

“The A/C just needs a charge”

No, the A/C system needs to be repaired. A functional system doesn’t need to be regularly filled with refrigerant.

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beat me too it! I get this one daily!

Or “I added some refrigerant(of course with stop leak from the auto store) to it and it still blows warm.”

A/C blows hot…“is there a relay I can check to just get it working again?”

Check engine light is on…pulled codes and it needs (insert most common sensor one thinks about here)

“Dont worry about the air filter I put a K&N in it”

“Just change the oil filter cause I use synthetic oil”

For diesels it “needs an EGR valve”

“Its a diesel, its good to let it idle and not shut off”

When the transmission service interval in the manual is 100k “you need to service your transmission at 30k or the warranty is void”

I better stop as I could go on all day :laughing:

So i get a call, guy needs the 70 ignition switch. I make one up. He delivers it to the restoration shop. The kid working on the car calls and wants the old shorted & melted switch back.
I ask why?
He states I gave him a left hand switch & he needs a right hand one.

He insisted on “rebuilding the melted switch”…

The car is now here. Delivered with the dash torn apart & harness dissected. Steering column trim is removed.
!! both bright head lights are blown (white at top inside both matching pattern) !! My guess, they pinched the headlight harness?

Oh, did I say the shop just painted the car. The tow truck driver pointed out 2 nicks in the dr door when he picked it up & documented them.

More to come… New top already lifting at the rear window bottom pass side?- Incorrect trim too!

Turning wrenches in the 70s/early 80s I heard some doozies. I don’t recall any REPAIR myths but MILEAGE myths were plentiful:

Loosen the real brakes for better gas mileage.

Back the front wheel bearing nuts off 1/4 turn from the factory spec - for better gas mileage.

Remove the fresh air intake duct ‘so the carb can run leaner’ - for better gas mileage.

Inflate new tires to 36 psi (not a good idea in west TX) for - you guessed it - better mileage.

Oh yeah - anyone remember the magnets on the fuel line - for better gas mileage? I think that one made a comeback not long ago.

Hot Rodding myth: You can install a 4bbl carb on a 2bbl intake by flipping the the 4 to 2 adapter upside down. As I recall this also gave you a ‘high rise’ intake.

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A few more:

Thinking that you need a spring to keep the lower radiator hose from collapsing. I think they gave up and just started putting them in the hoses…

Thinking that you have to slow down the circulation of coolant to give it “time to cool off” in the radiator.

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Me telling my wife “I need to fix something on the Cougar, it’ll only take 20 minutes.”

…and I already have the part!

Well, my old MG, would get hot when highway driving. Checked the thermostat- missing. Fitted one, and now overheating on highways!!,

1000 CFM carburetors
Electric fans and aluminum radiators.

Let the Holy Wars begin…

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Those items have a place. A DUI GM style HEI distributor in a Ford does not. It’s a mammoth overbearing waste of space that gains you NOTHING over a Ford Duraspark. To make this non-Ford non-sense work you need full length GM style cowl induction just to shut the hood over that garbage can with plug wires.

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For newer cars…a scanner tells you how to fix the car. …Nah, there is a bit more to it than that.

There’s a reason GM hides those in the back.

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I remind myself that everything that goes wrong with old cars still goes wrong with new cars, and a whole bunch of stuff can also go wrong that wasn’t there on old cars.

This goes the other way as well. Guys will pull dtcs and just shotgun the part at it rather then diagnosis it first.

Its not getting easier either. Ive seen codes lists quadruple in size over the years. Many have several paths to repair and many possible parts at fault.

Old cars are a bit easier but they have their faults too. Its all relative.

Another one that’s popular here is installing a “COLD” air intake. Almost always they cause a power reduction rather then gain.

Yeah, cold air intakes aren’t a gain. They just make more noise and in a perfect scenario might give 5 hp on top that you wouldn’t notice. Plus, It uses a cotton gauze type of filter which is o-k. But, when people over oil the filter it puts oil deposits in the Mass Air Flow insulating the heated wire causing erroneous information to the computer, wrong calculations then poor commands to engine and transmission operation. Sometimes transmission damage.

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Speaking of 5 more horse power.

When I was a kid, those Splitfire spark plugs came out and claimed “5 more horse power!”. I put them in my 6 hp Evinrude outboard. Even though the engine was now 11 hp, it was no faster than the 6 hp.

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The biggest of all for classic cars… “Yes, You can drive your car to our paint shop and we will disassemble as needed, paint it and reassemble after paint”. Unless his name is John Benoit, Scott Taylor, Marcus Anghel or Ed Myers you will be in for a huge heartache in most cases. When you deliver your classic it should have 4 rollers and vise grips for a steering wheel and NOTHING else. Want to leave your wiring harness in? Go ahead if you want it body color. I have heard countless stories of missing, swapped or damaged parts. Often you have to show up with a sheriff just to get what you can back. Nobody but you will take the time needed to reassemble it the right way. This is why many folks look at a car needing paint as “totaled”. Also why the “patina” look is so popular.