MAHLE heats up thermostat coverage as technology boosts engine efficiency

Electrically assisted thermostats are integral to thermal management and reduced emissions

Farmington Hills, Mich.—MAHLE is moving more and more toward being a systems supplier in thermal management, as evidenced by its pending acquisition of Delphi’s U.S. thermal management division, expected to be completed in the fall. The move illustrates the company’s stand that comprehensive thermal management systems, and thermostats, in particular, will play an increasingly significant role for combustion engines of the future.

“There will be increased demand and increased need for electronic thermostats, both for passenger cars, light trucks and HD applications, as they are integral in increasing engine combustion efficiency and reducing emissions,” said Bill McKnight, team leader-training, MAHLE Aftermarket Inc.

For import vehicles alone, MAHLE offers 130 thermostats that cover more than 42 million VIO (vehicles in operation). “A ballpark figure for applications covered is 500,” he said. “By the end of July, we’ll have 147 total active thermostats in the line that will cover over 54 million vehicles in operation, with about 550 applications covered — that’s a conservative estimate.”

As CAFE standards and requirements loom and greenhouse concerns build, the electronic thermostat lowers emissions and improves fuel economy by keeping engine temperature relatively high.

McKnight explained how.

Thermostat functions are controlled by an engine’s electronic control unit (ECU), ensuring precise regulation of temperature based on the engine’s loads. The combustion process in a passenger car engine runs optimally at an operating temperature of approximately 230 degrees Fahrenheit. However, in older engines the engine temperature was kept below that ideal temperature level to prevent component damage. Since an engine requires a certain power reserve, especially when operating at full load, conventional thermostats start to open at an engine temperature of approximately 110 degrees Fahrenheit by opening the coolant circuit and is fully opened by about 210 degrees.

The most basic type of thermostat is a by-pass valve thermostat, which has a sensing element containing a wax and aluminum mixture that expands when heated. When the engine is cold, the wax is solid and as engine coolant heats up it expands, the sensing element slides, opening a valve and allowing coolant to flow to the radiator. A tension spring presses against the sensing element and closes the valve when the operating temperature falls below the opening level of the thermostat.

The open temperature setting of a conventional thermostat, however, can only be adjusted slightly by changing the wax compound, but an electrically assisted (or “map-controlled”) thermostat provides broader and faster operation than traditional thermostats.

“In addition to the mechanical function of the wax element, electrically assisted thermostats incorporate an electric heater within the sensor, controlled by the vehicle’s ECU,” he said, “which receives information on the speed and load conditions of the engine. It uses that information to regulate the temperature of the coolant. A data set, or “map,” is stored within the ECU to govern when and how heat is added to the wax element to ensure optimum engine performance.”

Consequently, the thermostat can influence the temperature considerably more quickly, allowing the engine to operate in various load and operating conditions within the corresponding optimum range, improving engine efficiency and reducing emissions.

“As is the case with conventional thermostats, electrically assisted thermostats are not subjected to materials wear — they’re maintenance-free and designed to last for the entire engine service life,” McKnight said. However, he added that external factors such as the use of low-grade coolant and failure to regularly service the coolant can lead to material failure. Other possible causes of failure include previous damage caused by thermal overloading or contamination due to work carried out on the cooling system, such as when replacing the coolant or water pump, the cooler, the coolant hose, timing belt or accessory belt.

McKnight advised that when replacing faulty parts in a cooling system, thermostats and/or integral thermostatic housings should also always be replaced at the same time, because any loss of functionality or even complete failure can have severe consequences, including engine damage.

“Thermostat installation is relatively easy,” he said, “and most modern MAP thermostats are integral units where the gasket is molded into the thermostat body and designs incorporate load limiters to prevent over tightening the parts.” McKnight added that as with all MAHLE Aftermarket parts, there is 24/7 online tech help and a toll-free Engineering Service number for technicians who have questions.

“A technician’s primary concern is the reliability of the thermostat supplier and its OE experience,” he said. “MAHLE’s been in business since the late 1920s and our OE business in thermal systems will exceed $2 billion in 2015. Obviously, we understand the business and how to make very good parts.”

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