Basically, all you really need for your bus is a speedometer, an oil pressure gauge and a water temperature gauge. Everything else described herein is an add-on to the degree you want.
Some of the gauges and monitors are for eye-wash and others for a dazzling effect. Then there are those of us who are compulsive wanderers who are compelled to know the condition of everything. Then there are those old ex-airplane drivers who have developed the habit of scanning the instruments and without all these doodads to look at would feel lost. There is a certain level of satisfaction to feel that we have created our cockpit to closely resemble a Boeing 747.
This is the Preface to Dave Galey’s Book The Gospel of Gauges. In it he explains all of the information you need to know about the basic gauges, instruments, and monitors required in a bus conversion.
To read the entire book, go to our website and select the Members tab and choose Books on PDF. You will have to log in to read this book in Flipbook format and you will find it an enjoyable read.
I have yet to find an older bus with a fuel gauge that works. The Eagles, as an example, use VDO instruments. Their fuel gauge sender is a float inside a vertically oriented tube about 22" long. With a new sender and a new gauge, an indication of fuel on board is reasonably accurate. With age, however, these senders often become stuck in one position, or the wiring comes loose or gets knocked off.
The Stewart-Warner fuel gauge is not suitable in many cases, since it uses a “broken arm” type sender, similar to a float valve in a toilet. This float stays on top of the fuel changing the resistance of a rheostat at the hinge point with the instrument needle reflecting the changing voltage and calibrated in quantity, that is, empty, ¼, ½, ¾, and full. The reason this sender will not work is the internal baffling in the tank will interfere with the sender not allowing it to operate. This problem can be eliminated by having a custom tank fabricated.
Another approach to accurate fuel management is a dipstick similar to that used to check your oil. Again, you must compensate for the baffling and use a flexible dipstick. A piece of steel strapping material works well in this application. The stick or strap then only needs to be calibrated for gallons. Using the formula: (Width x Length x Height [in inches]) divided by 231 will give you the number of gallons in the tank. Fill the tank and mark the dipstick. Mark the stick in 5-gallon increments and you will always know how much fuel you have and you will be able to determine your fuel economy.
And then, there is the old-fashioned sight gauge which is nothing more than a transparent tube connected to a pair of fittings at the top and bottom of the tank. This is probably the most accurate form of fuel gauge available.
Another form of liquid level gauge was brought out a few years back. It is simply a tube inserted into the tank with an open end near the bottom. As the tank is filled, a level of pressure is generated inside the tube as part of the liquid attempts to penetrate the tube causing a gauge to react to the increased pressure. In effect, the gauge is reading the difference between atmospheric and hydrostatic pressure. When the tank is empty, the gauge will read zero because all there is is atmospheric pressure; when the tank is full, the gage will read the hydrostatic pressure of the number is inches of the liquid type and read this figure as being full. All the gauge has to be calibrated for is empty and full.