Whether your boat is brand-new or decades old, you should give some consideration to your engine gauges. On some new boats, builders have eliminated several gauges in favor of the so-called "idiot lights" to hopefully alert the skipper of an engine problem, while older boats may have gauges that have simply grown inaccurate or inoperative with age.

Either way, engine gauges are your first line of defense against very expensive engine repairs, and they can also help you extend the life of your engine, improve your speed, and get better fuel economy, too. The good news is that any boat, new or old, can easily be fitted with a full selection of new gauges that will not only monitor your engine accurately, but make your dashboard look like new, too.

Why do builders install idiot lights instead of gauges? The answer, unfortunately, is simple: they cost less. There is a saying among car enthusiasts that idiot lights tell you something has happened, while gauges tell you something is about to happen. Obviously, you (and your wallet) want to know about a problem before it occurs. A gauge is your only source of reliable information on what is occuring, what has occurred (such as a battery drain), or what may occur (such as overheating).

Take the fairly common boating situation where a piece of plastic bag or seaweed clogs the water intake to your engine cooling system. With the inflow of water stopped, your engine will begin to overheat. As the temperature climbs higher and higher, it has to reach a predetermined point before the idiot light blinks a warning. At that point, you may not have done any serious damage to the engine, but you've probably burned out your water pump impeller, which ends your boating for the day. With a temperature gauge, however, an alert skipper would have seen the first increase of engine heat long before the impeller was a melted lump, and could have stopped the engine to clear the blockage.

Pilots, whose lives depend on their engines, know that most engine failures are not sudden catastrophes. Instead, most problems develop slowly and telegraph the warning signals in ample time to take action.

While old engine gauges were often mechanical, modern gauges are almost entirely electrical, which means they're easy to replace. A gauge consists of two parts: a sensor or sending unit at the engine, and a display or dial on your dashboard. In between is a light wire that you can route easily to reach the dashboard. Let's take a look at some of the gauges you already have, and a few you probably need.

The tachometer displays the crankshaft speed of your engine, and is best used to pinpoint the best operating range for your engine, as well as make sure that you don't exceed the maximum rpms. Unfortunately, tachometers are often wildly inaccurate, so a quality tach can show you the right cruising speed as well as keep you from over-revving your engine. Tachometers can be analog (dial-faced) or digital, with numeric read-outs, and the choice is yours. Digital units tend to be more expensive, but they are more precise — down to a single rpm — than analog.

There is no single most important gauge, but the water temperature gauge comes close, since it monitors the cooling system where you are likely to have the most problems. As in the example mentioned above where the cooling system was blocked, an overheating engine can quickly lead to a serious and expensive meltdown of your engine.

An oil pressure gauge is popular among high performance boats since it gives you an immediate warning of an oil pump failure, a broken hose, or a leaking gasket. Since the absence of oil is just as dire a circumstance as overheated oil, the pressure gauge is a valuable tool.

An oil temperature gauge is much like a thermometer for a doctor — any fluctuation from the norm is cause for concern. Since too much heat will lead to burnt bearings, the oil temperature gauge is particularly useful for diesels which run hotter than gas engines.

Most boat owners are confused by what the electrical gauge on their dashboard is actually telling them, and part of that confusion is because there are two types of electrical gauges.

The first, and the most common on production boats, is the ammeter, which measures how fast the electrical energy is running into or out of your battery. It primarily shows the status of your alternator: a continually high reading suggests a battery that isn't taking a charge, while a low reading may mean a loose drive belt or an alternator failure.

The voltmeter, on the other hand, monitors the battery condition at a given moment, providing a reading of whether you have enough power to start the engine. While you'll rarely have high voltage, a low reading means your battery is nearly dead. You should probably have both an ammeter and a voltmeter to get a clear picture of your electrical system.

Your fuel gauge is, in all likelihood, laughably inaccurate and you'd probably know more simply by thumping the side of the fuel tank to see if it sounds empty or full. To be fair, the sender float in the tank has to endure slosh, vibration and the motion of the boat but, even sitting on the trailer, you may not get a good reading. You can calibrate many gauges by filling your tank in precisely measured amounts, but a new sender and gauge may be needed first.

An engine hourmeter is a simple electrical counter that records the time that your ignition is active, which is a good reason not to leave your key switched on with the engine off. Engine hours can help you keep track of your maintenance intervals and, at resale, can show that the buyer how much you've used your boat.

Two other gauges that you might want to consider include a drive temperature gauge for your stern drive, which helps protect the expensive outdrive on your transom by showing when the oil temperature is climbing into the worry range, and a fuel flow meter, which will show you the most economical cruising speed for varying loads and conditions.

When adding or replacing gauges, the size of your dashboard and the existing openings are going to dictate some of your choices. There are no standard size gauges so measure the existing openings carefully if you want to have "drop-in" replacements. Otherwise, plan on using your hole saw to add new openings in the dash.

While the dial faces come in a variety of colors and finishes, you'll also want to be careful to make sure you get the proper sending unit, so you'll need the engine make, model and serial number on your shopping trip. By getting the right sending unit and installation kit, you're assured of both the proper fit and accurate readings.

As a last piece of advice, once you've determined the proper operating range for your engine on each gauge, rotate the gauge in the dash so that the needle is pointing straight up under normal conditions. In that way, you can turn the helm over to a novice with only the advice to make sure that all the needles are pointing up.