MAHLE's new Monotherm® piston offers lower piston weight and can withstand higher peak combustion pressures.

In 1988, MAHLE became the first worldwide producer of articulated pistons with the introduction of the Ferrotherm® design. With its forged steel crown, this piston design replaced aluminum pistons in all US Class 8 heavy-duty applications. U.S. production of the Ferrotherm® piston exceeded 1 million in 1999.
Compared to aluminum pistons, the Ferrotherm® is heavier. This limits its application in weight sensitive applications, most notably in "V" engines.

MAHLE is now proud to announce the development of the Monotherm® piston, a one-piece forged steel design that offers the advantages of Ferrotherm® without the weight restrictions. Beginning with the forging, a large circumferential slot is cut, separating the crown and skirt. The skirt remains attached to the pin bore strut at the 3:00 and 9:00 positions, providing a substantial increase in strength in this critical pull-apart area. Piston machining proceeds in the same manner as for Ferrotherm® with the addition of the skirt profile. Piston guidance in pin direction is provided by the skirt, allowing the fourth land to be cut back for improved oil drainage.

The cooling gallery is closed with cover plates, a design feature well-proven in Ferrotherm® applications. To address cavitation concerns, the possibility to offset the pin bore is retained.

Through careful design, including under-crown machining and pin optimization, Monotherm® has matched the reciprocating weight of its aluminum predecessor.

Other advantages have become evident during the course of design optimization. The pin no longer needs to support the skirt, making an additional area available in the pin support region. This space can be used to increase bearing area to allow higher peak combustion pressures, opening the door for additional increases in specific power and fuel economy.

With the use of MAHLE's latest cost reduction technology, notably micro-alloyed steel and bushingless pin bores, the Monotherm® is very cost competitive with previous generation Ferrotherm® pistons.