|Pennzoil-Quaker State Synchromesh is a unique transmission and transaxle fluid that is not API "GL" rated. It has an approximate gear oil grade of about SAE 80W and can be used when temperatures range from -40ºF (-40ºC) to 300ºF (150ºC). According to Pennzoil's product description it is "formulated with high quality paraffinic base stocks, a fluidity modifier, multifunctional performance additives, corrosion inhibitors, a foam suppressor and a shear stable viscosity index improver additive. It provides excellent oxidation stability, low temperature performance, excellent synchronizer performance and compatibility with yellow metals, such as bronze, brass and copper components found in manual transaxles and transmissions." This description makes Synchromesh suitable for use in some transaxles or transmissions where GL-4 gear oils are specified.
A post on the message board at http://www.oilanalysis.com found Synchromesh to consist of a 5W30 non-detergent oil with a friction modifer and an EP (extreme pressure) additive. It is made under contract for General Motors by Pennzoil (APC 3378) or by Texaco (Code 1874 MTX Fluid).