Polyalkylene glycol: a synthetic built from ethylene and propylene oxide, used in worm gear oils, gas and refrigeration compressors, water-glycol fire-resistant hydraulics and food machinery. PAGs give low traction, high VI and almost no deposits because they break down into volatile products instead of sludge. Conventional PAGs do not mix with mineral oil or PAO, and some attack common paints and seals, so an accidental mix-up causes gelling, foaming and failures.
Worm drive is on PAG, flush it twice before anyone puts mineral gear oil back in there.
Interior paint on older gearboxes can lift and flake into a PAG fill, so check the housing coating before converting.
Also heard as
- polyglycol
- polyalkylene glycol
Related terms
Base oil group
Five-group system that sorts base stocks by saturates, sulfur, viscosity index and chemical type.
PAO
Polyalphaolefin, the synthetic hydrocarbon base oil built from alpha-olefins and classed as Group IV.
Ester
Synthetic or natural base oil made from acids and alcohols, valued for solvency, film strength and biodegradability.
Grease compatibility
Whether two greases can be mixed without losing consistency, dropping point or stability.