RE: [Chevelle-List] Electrical vs Mechanical gauges

[396guy]

I don't know the physics of them all, but I'm sure someone here does if you really want to get into the workings.  But, I'm simple so I'll leave the physics out.   Electrical temp and pressure gauges use a sending unit to measure temp or pressure.  Physics go on inside the sender and a current is sent along a single wire to the gauge which reacts.   Mechanical gauges have a physical connection to the engine.  Water/oil temp gauges use a gas filled tube that expands with heat thereby activating the gauge.  Pressure gauges have a copper/plastic/rubber line that runs from the item being measured to the gauge.   Electrical advantage: Generally easier to install due to the single wire running from the sending unit to the gauge. Less of a hassle to install since a couple of small gauge wires are all you have to thread through the dash to the gauge(s) themselves.   Electrical disadvantage: You are relying on electrical power (and a good ground) to give an accurate reading. Electrical gauges for temp and pressure generally have a smaller dial "sweep" about 90 degrees or so, from low to high readings. Either the gauge or sender can be replaced if it malfunctions - reducing cost of replacement.   Mechanical advantage: Generally have a 270 degree "sweep" of the dial giving more precise (read that as readable) readings. In the case of temp gauges, they remain functioning when the engine is shut off.   Mechanical disadvantage: In the case of oil/water temp gauges, the tube usually comes in 60" and 72" lengths and IT CANNOT BE CUT to fit since it's a sealed tube, leaving excess tubing to hide. If the tube breaks, the gauge is junk. Since the gauge, tube, and engine adapter(s) are one long piece, you have to start threading the assembly from inside the car out and usually requires a 3/4" to 1" hole in the firewall to get the adapter/fitting through. In the case of an oil pressure gauge, there must be a physical connection (line) between the engine block and the gauge. Some people are just leery of running a little 1/8" line inside their car with 30, 40, 50 or pounds of oil pressure. I've never had one break, but others have.   Then there are gauges that can only be mechanical (vacuum comes to mind) and some that can only be electric such as ammeter or voltmeter.  A fuel pressure gauge can even be both.  If you mount the gauge INSIDE the car, you have to run a line (like the oil pressure) to a sender under the hood and it converts the pressure to an electrical signal to run inside the car.  Definitely don't want to chance a broken fuel line under the dash or in your face.  You'll see a lot of racers with oil and fuel pressure gauges on the outside of the car just in front of the windshield. It gives the accuracy (?) of a mechanical gauge but it's outside if anything breaks.   Whew!  Sorry for the long wind...:*) Dale McIntosh ACES #1709/TC #92 Gold 67 SS/67 Elky http://www.dalesplace.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Michael Ishee Sent: Monday, January 14, 2002 11:16 PM To: Chevelle Mailing List Subject: [Chevelle-List] Electrical vs Mechanical gauges What is an electric and mechanical gauge and what the differences, benefits, etc. Michael