Hot answers tagged

10

A simple test that you can perform in your own driveway is: For each corner of the car, push down hard several times (the car should be bouncing visibly up and down) When pushed down, release and watch The car should bounce upwards (above the normal resting point) and then immediately settle at the resting point. Additional bouncing indicates worn or faulty ...


9

I've posted this graphic before, but I think it's pertinent here as well: This is an image of a graph which Carroll Smith put in his book, Engineer to Win. In the book, one of the sections talks about metal fatigue. In this specific graph, he's talking about how stress affects any given metal part: how much will a part take before it fails. The graph ...


9

I see this completely normal and not a cause of concern. The service advisor's explanation is certainly a valid reason, but they could have needed to drive the car for a total of 19kms for many legitimate reasons: The service technician could not diagnose the source of the noise on his own, so he went back and picked up another service technician to help ...


8

Water in fuel is easy to figure out. Put a sample (say 5 to 10 ounces) of the fuel into a clear glass container. Let it sit. If it separates into two layers, you have water in the fuel. Shown: an obviously contrived example of gasoline (10% ethanol) with approximately 2 ounces of water added - water has visibly sunk to the bottom of the jar.


8

Compression test is more to test if there is a problem. If your compression is low, it could be a number of different issues. You can test the rings by adding oil to the cylinder and see if the compression is higher. Other than rings it can be difficult to determine the source of the issue. A leakdown test will tell you where the problem is. By watching ...


7

In general, the max speed in the manual is a guide to tell you how fast it's capable of going. It's likely lower than what it's actually capable of since most buyers won't file suit if a maker under rates a car. There is always a little margin in that so I would not be concerned if you drove a bit faster than the max in the manual. I wouldn't make a habit of ...


6

Fun fact: the average mid-sized car tire sees ~800 revolutions per mile, so every component of a 50k mile tire must endure more than 40 million loading/unloading cycles! (note: some tires are not guaranteed for 50k miles). Source + testing information can be found in the PDF titled 'The Pneumatic Tire' on this page. Regardless of mileage rating, all tires ...


6

In the US, the NHTSA (National Highway Traffic Safety Administration) is the governing body that controls testing and specifications of motor vehicles. They mandate that a certain set of standardized tests are carried out on all tires sold for highway use. Tires that are made for off-road equipment and possibly some trailers might not have to undergo the ...


6

"Hand priming" or actuation is effectively worthless as a gauge on the performance of a Shock/Strut Assy. Only when severely damaged or out of service will the activity show any truly noticeable difference. And by priming the shock, you're effectively wasting your time. It will do so on its own. The reason why this "works" is occasionally air or gas may slip ...


6

The federal test procedures for vehicle emission certification(FTP) is run on a dynamometer. It starts with the vehicle at an exact temperature and barometric pressure and humidity. It is run in a lab that has carefully controlled exact air conditions that are maintained throughout the test. The vehicle is kept is stored at the test temperature for hours ...


6

No - that's all you need to test. Now drive the car to a nearby garage and get them to do a front-end alignment on it - you won't have gotten everything exactly where it needs to be, so let them fix it to specification. As an added bonus, it puts a fresh pair of mechanics eyes onto your work, so after it's been aligned, you know that everything is good.


5

Honda Coil Over Plug setups have three wires. As mentioned they have an internal Ignition Control Module. Pins 1 & 2 are power and ground while pin 3 is the control signal from the Electronic Control Module. You can test coil resistance with a multimeter. How to Test an Ignition Coil with a Multimeter You can also check the primary coil with a digital ...


5

Yes it can. The reason is, these are two different tests, done differently, reading different things. To understand this, you need to understand how the tool works for each test. For the compression test, the test apparatus captures and holds the compression as it builds through several, but counted revolutions of the crankshaft. You will get so much ...


5

You'd backprobe the S and L terminals with the connector plugged in. So attach one end to a ground point and the other to the S or L terminal. Basically the S terminal is the Field terminal. The S wire gets power from the eng inj fuse and should have 14+V while the engine is running. The alternator grounds the L terminal when voltage is below threshold and ...


5

I've been wondering this too as a lot of overheating related questions come up. There are 2 ways water pumps fail - leaks and impeller failure. Leaks can typically be seen, so they are easier to diagnose. Impeller failure is difficult to detect. Typically, the engine will overheat, but the heater core and radiator will still be cold. With a thermostat ...


5

Hand Priming Shocks of Various Dampeners/Struts is Urban Legend This myth has been perpetuated over time and has gained legs and therefore credibility. Yes, it's true that the gas and oil separate on the shelf lying horizontally. It's also true that they separate on the shelf if stored vertically, piston rod up or down. But it doesn't matter. These ...


4

Take the left side wheels off, bolt them on backwards, and turn the car upside down... Seriously, @spicetraders nailed this in the comment. the US DOT date codes [WeekWeekYearYear] are only hot-stamped on one side, even though the raised oval or delineated area is part of the tire mold on both sides. Because you new Goodyear Vector AS are directional, ...


4

There are two things that professional battery testers can measure. One is to somehow based on the voltage measure the charge level. Another is to measure cranking amperes. Of these, the second measurement (cranking amperes) is accurate. Unfortunately, old batteries don't die by having reduced cranking amperes: they die by having reduced capacity. So, the ...


4

I have often heard this term as well, but have never known the technical reasons or the actual root cause of what is known as a "surface charge". To figure it out, I took a gander at a website called the "Battery University". They state the following about a surface charge: Lead acid batteries are sluggish and cannot convert lead sulfate to lead and lead ...


3

In Europe, only tires with an EU Tire Label are allowed to be sold. Big brands were initially happy for the introduction of this label, but were disappointed about the results. Those "crap" Chinese tires were performing almost equal with the big brand tires, but cost half as much. A lot people say "it's your safety don't do it". The companies would be very ...


3

The max speed a vehicle is rated for usually depends on the speed rating of the tires equipped by the OEM. The vehicle can move faster, but the tires are not rated to go faster.


3

One pump; one pump only. Which test we perform determines the procedure used. Three procedures are described and each test has a different purpose. But keep in mind when the engine is running it only gets one pump per cycle. Running compression test: A decent way to estimate volumetric efficiency (VE). This is not technically a compression test. Install ...


3

In my home state of Colorado, we are required to get emissions tests on our vehicles every two years (after they are a certain number of years old). They way they do this is they place the car on a dynamometer (like a treadmill), put the car in gear, and bring the wheels up to a certain speed. They have a fan placed in front of the car to help cool it down ...


3

A cylinder leak-down tester is a completely different animal than a combustion leak detection kit and has a completely different job. While the combustion leak detector checks for carbon-dioxide (CO₂) in the radiator. The cylinder leak-down tester kit hooks up to to your cylinder through the spark plug hole on one end and to your compressor on the other. You ...


3

Backprobe the injector signal wire and use that to activate the injector. Let the ECM or relay handle the power side of things.


3

The Lambda readings are slightly lean but within the acceptable range for normal catalytic converter operation. The CO is in the normal output range for an engine that is running normally and within acceptable fuel mixture limits. That it to say that the engine appears to be running normally and no repairs to it would improve the exhaust gas output makeup. ...


3

If the system you are working on has a sealed radiator, with an expansion tank instead of a surge tank, with the only working pressure cap on the expansion tank, then yes, insert the tester in that opening instead. The way these testers work is they test for hydrocarbons in the coolant system. If the engine is sealed correctly, there WILL NOT BE ...


3

The owner does not post the reports or results of the mot on the gov website - it comes from the testing station and the tester. The tester may be able to exercise their judgement about posting advisories or not, but the standard report will be complete.


2

I would say that if the overflow tank only has a small hose from the over pressure nipple on radiator right under cap then that is normal and you should put the tester right on the radiator cap mouth, as the overflow isn't a reservoir and won't be getting circulation from coolant system until the cap is over pressurized. As opposed to a reservoir or ...


2

The best (read: easiest) method to check this is doing it on vehicle. In that case, you put a fuel pressure gauge on the engine at the Schraeder valve (if so equipped) and check the fuel pressure at idle and ensure you have the proper pressure. Then pull the vacuum line to and check the pressure again, which should have changed (it should go up between 5-7 ...


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