How to tell an honest mechanic

Hubby has a 2001 Passat with 245,000 miles. It suddenly started running so roughly that it shakes, but only when you accelerate. No roughness or shaking when you let off the gas. Mechanic says it needs a new chain tensoner and a coil. Total cost estimated at $1,600. How can we be sure this is what the car needs? Not sure I trust this guy. $1,600 is a lot, but still less than a new car. An aquaintance thinks it just needs a new fuel filter.

You need a proper assessment from a good mechanic who knows VWs and knows what to inspect. To my knowledge, your car has a timing belt with a tensioner, and an accessory drive belt outside the engine, also with a tensioner. Which one is it? For a timimg belt, water pump and tensioner, budget $800+ for a Passat.

At 245,000 miles you will be on your 5th timing belt or so, and probably your 3rd water pump.

It’s entirely possible that the car needs a new belt tensioner, a new coil, and a number of other things. What maintenance has been doine so far on this vehicle?

You normally get a neat, itemized list from a good mechanic who will also physically show you, if possible, WHY something has to be replaced.

Rough running can be caused by a large number of things, and I doubt if what the mechanic says you need will cure the shaking. He will just try something else when that happens. You’ve heard of quack doctors, I’m sure; “if this does not work, may that will”. A bad tensioner usually does not cause rough running.

I would still budget $1600 at least since at your high mileage you may need a number of things your “mechanic” has not been able to think of.

Anytime a vehicle has an engine performance problem Step One should be a compression test. You always weed out the possibility of a mechanical fault (meaning serious engine problems) before throwing any parts at it.

You might get a parts house like AutoZone to scan the car. They will do this free. Post any results for discussion.

At this point there’s not enough info known about this problem to even make a wild guess. Both the mechanic and your friend have valid points and it’s possible the car could need all of that and even more.

Thanks. This is great -just like having relatives who are car savvy. Will get more infor from the “mechanic” and will get him to do a compression test as suggested by ok4450.

I would simply get a 2nd opinion if you 2nd guess your mechanic when work is expensive. Do not mention prior diagnosis as it will throw the next person off possibly.

I do not think your mechanic is dishonest by any stretch. That is harsh. They are giving a best educated guess based on symtoms, actually checking and hopefully experience.

Agree that there are far more incompetent mechanics than dishonest ones. They often become dishonest when their fix does not work or they break something in the process of trying to fix your car.

The always sticky part is this. A mechanic often faces a car that he has never seen before and has no idea of any history behind that car.

In this case, he faces a car with nearly a quarter of a million miles that could legitimately need 15 things to make right and that’s assuming the engine itself doesn’t have any problems.

It needs a coil? Maybe it needs a coil because of a faulty plug wire. Maybe it needs new wires because of a faulty plug. Maybe it needs any potential plug-killing items corrected which could be anything from oil burning to excessively rich mixture due to any one of a 100 things to low compression or even a partially clogged catalytic converter.
Things like this are not always in black and white.

Did the mechanic take the car for a test drive, or just give you an estimate based on your description? Does the engine shake at high rpm, or just when under the load of acceleration? Without a test drive, it’s just about impossible to eliminate other possible causes for this problem.

For example: you might want to have somebody also look at the CV joints. The symptom you describe is similar to what happens when one of them is on the way out. The key here is that when not under acceleration, the car runs smoothly (less torque on the CV joint itself).

They are all honest, until proven otherwise, just like cops,lawyers,judges,butchers,bakers,candlestick makers.

I don’t know if the mechanic did a test drive, but will find out. The car shakes under the load of any acceleration, and it does run smoothly when not under acceleration. Shaking does not appear to increase with increased acceleration.

Doctors are wrong far more often than mechanics…

Okay, here is more information on the car. A new timing belt was put in about 25,000 miles ago by the same mechanic. At our request he has performed a compression test and provided these results: 110 dry, 170 wet, #2 cylinder is weak.

Does that help define the problem?