Keep an Eye on Overheating

Temperature can provide an early alert to problems in a variety of onboard areas.

Temperature is often the first and easiest-to-find indication of a developing problem and can quickly be used as a screening technique for situations that may benefit from further analysis. Affordable handheld infrared (IR) pyrometers — $40 to $100 — make this an easy preventative maintenance task.

Overheating-Engines-03We have a rule aboard Easy Goin’ that states “everything must serve two or more purposes.” A handheld IR thermometer, also known as infrared pyrometer, easily fits the criteria. The noncontact thermometer instantly measures surface temperatures in hard-to-reach or hazardous areas without contact. It also works well to determine the temperature of the barbeque.

The variety of onboard uses is nearly limitless: it can measure moving objects such as fan belts and propeller shafts, live electrical circuits (AC and DC), the stuffing box, batteries, cables, switches, circuit breakers, alternators, oil pans and hoses. You get the idea.

IR thermometers are able to measure the temperature of objects without making direct contact, because they specifically measure the energy being radiated from an object. Every object whose temperature is above absolute zero (-273.15C or -459.67F) emits infrared energy. The hotter an object, the more infrared energy it emits.

In simple terms, the basic components of a IR pyrometer are an optical system, a detector and a processing unit. The infrared energy emitted from an object to be measured is gathered by the optical system and then passed through a detector that transforms the infrared energy into electrical signals. These signals are then changed in the processing unit into a temperature measurement, which is displayed on the unit.

Most units are shaped like a gun and are operated with a trigger. A laser assists the user in aiming the pyrometer at the object whose temperature is to be measured. The units are easy to use. To locate a hotspot, aim the thermometer outside the area of interest, then scan across with an up and down motion until you locate the hotspot.

As useful as infrared pyrometers are, they’re often misused. The most common fault involves the unit’s field of view. Many users believe that the area being measured is only as large as the laser dot. In fact, the pyrometer measures a cone-shaped area, and the temperatures of all objects within the cone’s footprint are averaged. Because the footprint grows as the meter is moved farther from the object being measured, it’s best to get as close as safely as possible to the object in question.

IR pyrometers cannot measure through transparent surfaces such as glass; they will measure the surface temperature of the glass instead. Inaccurate readings will also occur from measuring shiny or polished metal surfaces (e.g., stainless steel, aluminum, brass and copper). To compensate, cover the surface to be measured with masking tape or flat black paint.

The following are some normal operating temperatures (in Fahrenheit) that might be helpful in determining potential problem areas:

– Alternator outer case and pulley: no more than 200 degrees while in operation. The Stator may operate at 250. If it’s hotter, it’s being overworked and overcooled, which can be an indication that you need an alternator with a higher duty rating.

– Engine oil: crankcase oil pan 160 to 220 degrees. A higher temperature may be an indication of a restricted or plugged oil cooler.

– Exhaust system: wet exhaust hose no more than 200 degrees. A higher temperature may indicate a clogged riser.

– Stuffing box: no more than 30 degrees above the ambient water temperature; dripless boxes often run somewhat cooler. If it’s warmer, the box is either overtightened or lacks sufficient water flow.

Transmission fluid: 130 to 175 degrees.For AC and DC systems, resistance to current flow creates heat; therefore, a pyrometer can be used to scan for weak and failing components such as batteries, connectors, cables, switches and circuit breakers.

Proper operating temperatures for other engine components may vary based on the manufacturer’s recommendations.


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