![]() The gauge interprets the changing resistance values to deliver a temperature reading. Basically, as the temperature around the sending unit fluctuates, the electrical resistance of the thermistor changes too. Inside the sending unit is a thermally-sensitive electrical resistor, or “thermistor” if you’re in a hurry. For the specific sending unit pictured above, you thread the sending unit into the engine’s water jacket or other coolant passage, then you connect the top terminal via a hookup wire to the gauge in the cabin. (Image/OnAllCylinders)Īn electrical water temperature gauge essentially consists of two main parts: the gauge and a sending unit, with a wire to connect them together. The threaded portion on the left connects via a wire to the gauge, the middle is how it threads into the engine, and the cylindrical portion on the right protrudes into the coolant passage. They don’t always look alike, but most work in pretty much the same way. How Does an Electrical Water Temperature Gauge Work? This is a typical sending unit for an electric coolant temperature gauge. The tube’s got a set length too, so if it’s not long enough to reach the gauge and where you want to install the probe, then you’ll have to find a new gauge or a different spot to put the probe. ![]() You’ll also want to keep the tube away from other heat sources, like blazing-hot header tubes, as ambient heat can affect the gauge reading. For that reason, many folks install the probe into a manifold or water neck where there’s more space for the probe to stick down into the coolant. It’s often larger than an electrical sending unit, which can make plugging it into a water jacket impossible. Another potential hitch with a mechanical gauge is its probe. If the tube breaks or gets ruptured, it’s often easier to just buy a new gauge instead of repairing the old one. The capillary tube needs to be routed through the engine and dash carefully, avoiding any sharp bends or kinks. That means you don’t have to worry about matching the gauge to its correct sending unit either.Īnd since it doesn’t rely on electricity, it’ll still deliver an accurate reading after the ignition key is removed, which can be handy if you want to see how heat dissipates when the engine isn’t running.Ī mechanical temperature gauge can be pretty easy to install too, just thread the probe though the inside, then out to the engine bay, and screw it into a coolant port.īut at the same time, installation can also be a big drawback for a mechanical temperature gauge. There’s one main advantage to a mechanical gauge-it requires no electricity (save for an optional backlight so you can see it at night). Pros & Cons of a Mechanical Coolant Temperature Gauge Note the black capillary tube that’s permanently attached to the back and the metallic probe on the other end that threads into your engine. The tube connects to the gauge and, on the other end, it terminates in a threaded probe that installs into your engine’s water jacket or other cooling passage.Īs the engine heats up and cools down, the gas reacts, then the gauge’s internal mechanism interprets the changes in pressure to deliver a temperature reading. That tube contains a gas/fluid that expands and contracts as the temperature inside the tube changes. ![]() Look at the back of a mechanical temperature gauge and you’ll likely see a sealed tube permanently attached to the back of it. It’s based on a design called a “ Bourdon Gauge,” but we’ll skip a lengthy scientific discussion on how it all works and just give you the basics. (Image/OnAllCylinders)įor starters, a mechanical water temperature gauge is technically a pressure gauge that detects changes in pressure related to the way a gas reacts to temperature fluctuations. How Does a Mechanical Water Temperature Gauge Work? Here’s the mechanical gauge we’re testing in this demonstration-it’s a well-used unit from an old Summit Racing gauge kit that’s been installed in a handful of different projects and is still going strong. A little while ago, we quickly alluded to the difference between mechanical and electrical coolant temperature gauges in a post about troubleshooting a radiator.īut this topic deserves a little more attention and we also thought it’d be helpful to show you how to test your electrical and mechanical coolant temperature gauges too. ![]()
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