What does RPM gage measure?
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Revolutions per minute. Basically how many times your engine turns over per minute at whatever throttle you're at. It usually measures spark from the ignition coil(s) on a gas engine, and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
Rpm measures Crank rotations per minute.
They are there just as another point of reference. The driver can see at what point to shift(manual)and whether there is any slip,which could indicate potential problems.
In the 70's and 80's they were in sportier type cars. Now they are there to make the driver think they are in a sporty type car.
They are there just as another point of reference. The driver can see at what point to shift(manual)and whether there is any slip,which could indicate potential problems.
In the 70's and 80's they were in sportier type cars. Now they are there to make the driver think they are in a sporty type car.
Originally Posted By: mechjames
Revolutions per minute. Basically how many times your engine turns over per minute at whatever throttle you're at. It usually measures spark from the ignition coil(s) on a gas engine, and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
What?
Revolutions per minute. Basically how many times your engine turns over per minute at whatever throttle you're at. It usually measures spark from the ignition coil(s) on a gas engine, and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
What?
Originally Posted By: Clevy
In the 70's and 80's they were in sportier type cars. Now they are there to make the driver think they are in a sporty type car.
In the 70's and 80's they were in sportier type cars. Now they are there to make the driver think they are in a sporty type car.
Originally Posted By: Clevy
Rpm measures Crank rotations per minute.
They are there just as another point of reference. The driver can see at what point to shift(manual)and whether there is any slip,which could indicate potential problems.
In the 70's and 80's they were in sportier type cars. Now they are there to make the driver think they are in a sporty type car.
Thanks for the info Clevy
So it measures the rotations/revolutions of the Crankshaft?
Personally, in automatics, I'd rather have other gauges that will give information I'm more interested in, such as outside temp, avg MPGs, more tripometers (use these to keep track of my fluid changes). I just don't see the need for a tachometer in automatics (then again, I'm not a mechanic. perhaps they are used to troubleshoot problems)?
Originally Posted By: Clevy
Originally Posted By: mechjames
Revolutions per minute. Basically how many times your engine turns over per minute at whatever throttle you're at. It usually measures spark from the ignition coil(s) on a gas engine, and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
What?
um, that really confused me too
I really don't understand "engine turning over." I'm quite sure it doesn't mean the engine is physically turning itself round and round under the hood. I'm not being a smartbutt here, I just really don't understand some of the jargon used in mechanic world. Thanks for the post, nonetheless, Mechjames
Rpm measures Crank rotations per minute.
They are there just as another point of reference. The driver can see at what point to shift(manual)and whether there is any slip,which could indicate potential problems.
In the 70's and 80's they were in sportier type cars. Now they are there to make the driver think they are in a sporty type car.
Thanks for the info Clevy
So it measures the rotations/revolutions of the Crankshaft?
Personally, in automatics, I'd rather have other gauges that will give information I'm more interested in, such as outside temp, avg MPGs, more tripometers (use these to keep track of my fluid changes). I just don't see the need for a tachometer in automatics (then again, I'm not a mechanic. perhaps they are used to troubleshoot problems)?
Originally Posted By: Clevy
Originally Posted By: mechjames
Revolutions per minute. Basically how many times your engine turns over per minute at whatever throttle you're at. It usually measures spark from the ignition coil(s) on a gas engine, and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
What?
um, that really confused me too
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For everyday driving by the masses they aren't much use...
Real car guys & girls use them to obtain max performance from their engines when shifting(yes even in a automatic)... All about getting a edge on the guy in the next lane(who's probably looking at his outside thermometer or trip minder anyway)...
Real car guys & girls use them to obtain max performance from their engines when shifting(yes even in a automatic)... All about getting a edge on the guy in the next lane(who's probably looking at his outside thermometer or trip minder anyway)...
Originally Posted By: Eosyn
So it measures the rotations/revolutions of the Crankshaft?
Yes.
This is a crankshaft:
This is a crankshaft in motion inside an engine:
The tachometer tells you how quickly the crankshaft rotates, or how many revolutions the crankshaft makes in 1 minute. And since the crankshaft is connected to other engine parts, it also indirectly tells you how quickly (how often) those others parts are moving (pistons, valves, etc.)
Quote:
Personally, in automatics, I'd rather have other gauges that will give information I'm more interested in, such as outside temp, avg MPGs, more tripometers (use these to keep track of my fluid changes). I just don't see the need for a tachometer in automatics (then again, I'm not a mechanic. perhaps they are used to troubleshoot problems)?
Many automatics have manual modes. In those modes, a driver often wants to know what RPM he's at if he's trying to squeeze the best acceleration/performance out of the engine. Each engine achieves its best performance in a specific RPM range.
So it measures the rotations/revolutions of the Crankshaft?
Yes.
This is a crankshaft:
This is a crankshaft in motion inside an engine:
The tachometer tells you how quickly the crankshaft rotates, or how many revolutions the crankshaft makes in 1 minute. And since the crankshaft is connected to other engine parts, it also indirectly tells you how quickly (how often) those others parts are moving (pistons, valves, etc.)
Quote:
Personally, in automatics, I'd rather have other gauges that will give information I'm more interested in, such as outside temp, avg MPGs, more tripometers (use these to keep track of my fluid changes). I just don't see the need for a tachometer in automatics (then again, I'm not a mechanic. perhaps they are used to troubleshoot problems)?
Many automatics have manual modes. In those modes, a driver often wants to know what RPM he's at if he's trying to squeeze the best acceleration/performance out of the engine. Each engine achieves its best performance in a specific RPM range.
Originally Posted By: TFB1
For everyday driving by the masses they aren't much use...
Real car guys & girls use them to obtain max performance from their engines when shifting(yes even in a automatic)... All about getting a edge on the guy in the next lane(who's probably looking at his outside thermometer or trip minder anyway)...
LOLOL ouch!
Quattro Pete, thanks much. the explanation and graphics helped a great deal!
Now to take it one step further, from the animation of the engine working, motor oil comes into play by lubing the moving parts of the crankshaft where it connects to the rod which connects the pisons? I can see if those parts aren't lubed, it could stick and not turn the crankshaft. Man, I'm learning lots here, thanks guys
For everyday driving by the masses they aren't much use...
Real car guys & girls use them to obtain max performance from their engines when shifting(yes even in a automatic)... All about getting a edge on the guy in the next lane(who's probably looking at his outside thermometer or trip minder anyway)...
LOLOL ouch!
Quattro Pete, thanks much. the explanation and graphics helped a great deal!
Now to take it one step further, from the animation of the engine working, motor oil comes into play by lubing the moving parts of the crankshaft where it connects to the rod which connects the pisons? I can see if those parts aren't lubed, it could stick and not turn the crankshaft. Man, I'm learning lots here, thanks guys
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Quattro Pete, nicely crafted reply.
Got me to thinking about it. For extra credit: on the standard 4-cycle engine, the crankshaft makes two revolutions to move the displacement of the motor. For example, with a 2 liter motor the crankshaft rotates twice to move 2 liters of air, a 350 cubic inch motor rotates the crank twice to move 350 cubic inches of air, etc.
The cam shaft rotates at 1/2 the RPM of the motor. In essence, because the camshaft controls the airflow through the motor. Interesting relationship between the parts.
Got me to thinking about it. For extra credit: on the standard 4-cycle engine, the crankshaft makes two revolutions to move the displacement of the motor. For example, with a 2 liter motor the crankshaft rotates twice to move 2 liters of air, a 350 cubic inch motor rotates the crank twice to move 350 cubic inches of air, etc.
The cam shaft rotates at 1/2 the RPM of the motor. In essence, because the camshaft controls the airflow through the motor. Interesting relationship between the parts.
Originally Posted By: Falcon_LS
Personally I could care less about the tachometer in an automatic. I'd rather have a proper coolant temperature gauge, which is now being phased out in favor of a warning light instead.
As long as it's a proper one and not an idiot gauge. All three of my vehicles have coolant gauges (one even has a transmission oil temp gauge), and all of them are idiot gauges. Have to use a scan tool to find actual temperature.
Actually, I'm going to disagree with you, and state that, on an automatic, I'd rather have one of those DIC (Drive Information Center) readouts instead of the tach or temp gauge. Well, I'd rather have all three, but if I could only have one, a readout which I could use to scroll through real time temps and pull trouble codes would be worth money to me. Would be nice if it was as configurable as a Scanguage (which can show four different measurements at once), but even just one reading at a time would be sufficent.
Personally I could care less about the tachometer in an automatic. I'd rather have a proper coolant temperature gauge, which is now being phased out in favor of a warning light instead.
As long as it's a proper one and not an idiot gauge. All three of my vehicles have coolant gauges (one even has a transmission oil temp gauge), and all of them are idiot gauges. Have to use a scan tool to find actual temperature.
Actually, I'm going to disagree with you, and state that, on an automatic, I'd rather have one of those DIC (Drive Information Center) readouts instead of the tach or temp gauge. Well, I'd rather have all three, but if I could only have one, a readout which I could use to scroll through real time temps and pull trouble codes would be worth money to me. Would be nice if it was as configurable as a Scanguage (which can show four different measurements at once), but even just one reading at a time would be sufficent.
Originally Posted By: supton
As long as it's a proper one and not an idiot gauge. All three of my vehicles have coolant gauges (one even has a transmission oil temp gauge), and all of them are idiot gauges. Have to use a scan tool to find actual temperature.
Actually, I'm going to disagree with you, and state that, on an automatic, I'd rather have one of those DIC (Drive Information Center) readouts instead of the tach or temp gauge. Well, I'd rather have all three, but if I could only have one, a readout which I could use to scroll through real time temps and pull trouble codes would be worth money to me. Would be nice if it was as configurable as a Scanguage (which can show four different measurements at once), but even just one reading at a time would be sufficent.
That's exactly why I have a ScanGauge-II on each and every vehicle. None of the gauges are really accurate - have you tried comparing your speedometer readout to your ScanGauge-II for instance?
I'm going to say, for the average person, they give you a brief idea of what's going on - but how many people actually look at their gauges when they drive?
As long as it's a proper one and not an idiot gauge. All three of my vehicles have coolant gauges (one even has a transmission oil temp gauge), and all of them are idiot gauges. Have to use a scan tool to find actual temperature.
Actually, I'm going to disagree with you, and state that, on an automatic, I'd rather have one of those DIC (Drive Information Center) readouts instead of the tach or temp gauge. Well, I'd rather have all three, but if I could only have one, a readout which I could use to scroll through real time temps and pull trouble codes would be worth money to me. Would be nice if it was as configurable as a Scanguage (which can show four different measurements at once), but even just one reading at a time would be sufficent.
That's exactly why I have a ScanGauge-II on each and every vehicle. None of the gauges are really accurate - have you tried comparing your speedometer readout to your ScanGauge-II for instance?
I'm going to say, for the average person, they give you a brief idea of what's going on - but how many people actually look at their gauges when they drive?
JHZR2
Staff member
Originally Posted By: mechjames
... and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
My 30 year old diesels use a hll effect sensor through an amp. The sensor is on the harmonic balancer external to the engine. Newer models used a similar pickup but inside the transmission bell housing.
... and charging output from the alternator on older diesel engines. I'm not sure what they measure on the new ones, possibly using a crankshaft position sensor or the cam position sensor with multiplication.
My 30 year old diesels use a hll effect sensor through an amp. The sensor is on the harmonic balancer external to the engine. Newer models used a similar pickup but inside the transmission bell housing.
VW intentionally has the speedometer read high; have not checked the Toyotas for that. Am a bit peeved at having to buy aftermarket equipment to read out what should already be available, but I guess that's life. Need to get around to buying another one of those SG's, one of these days, and stop moving it between vehicles.
I know what my gauges do, and I have to admit, I probably only look once/hour...
I know what my gauges do, and I have to admit, I probably only look once/hour...
Originally Posted By: supton
VW intentionally has the speedometer read high;
Source? That's a strange claim.
VW intentionally has the speedometer read high;
Source? That's a strange claim.
Originally Posted By: Rick in PA
Got me to thinking about it. For extra credit: on the standard 4-cycle engine, the crankshaft makes two revolutions to move the displacement of the motor. For example, with a 2 liter motor the crankshaft rotates twice to move 2 liters of air,
Not sure I follow. If you look at the animated gif above, each piston travels all the way down and all the way back up during a single crankshaft revolution (360 degrees). Why are you saying it takes two revolutions? Or are you referring to a different engine design than what's depicted above?
Got me to thinking about it. For extra credit: on the standard 4-cycle engine, the crankshaft makes two revolutions to move the displacement of the motor. For example, with a 2 liter motor the crankshaft rotates twice to move 2 liters of air,
Not sure I follow. If you look at the animated gif above, each piston travels all the way down and all the way back up during a single crankshaft revolution (360 degrees). Why are you saying it takes two revolutions? Or are you referring to a different engine design than what's depicted above?
OK, I am smirking here but a guy asked what is tachometer is measuring and you go on telling him about crankshaft! What an irony!! It is like when your 6 year old asks you where babies come from and you start explaining X and Y chromosome and cell membrane to her.
OK Vikas, why don't you put it in layman's terms then?
When someone earlier tried to put it in simpler terms and said it had to with with how fast the engine is turning, others laughed at him.
Quote:
OK, I am smirking here but a guy asked what is tachometer is measuring
The question was:
Originally Posted By: Eosyn
What exactly does an RPM gage measure? What is rotating at those RPMs?
When someone earlier tried to put it in simpler terms and said it had to with with how fast the engine is turning, others laughed at him.
Quote:
OK, I am smirking here but a guy asked what is tachometer is measuring
The question was:
Originally Posted By: Eosyn
What exactly does an RPM gage measure? What is rotating at those RPMs?
Originally Posted By: Vikas
OK, I am smirking here but a guy asked what is tachometer is measuring and you go on telling him about crankshaft! What an irony!! It is like when your 6 year old asks you where babies come from and you start explaining X and Y chromosome and cell membrane to her.
Maybe because a tachometer measures the crankshaft's revolutions per minute?
OK, I am smirking here but a guy asked what is tachometer is measuring and you go on telling him about crankshaft! What an irony!! It is like when your 6 year old asks you where babies come from and you start explaining X and Y chromosome and cell membrane to her.
Maybe because a tachometer measures the crankshaft's revolutions per minute?
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