I use Castrol "clearedge" semi-synthetic water soluble. Lasts in sump without going rancid, works great on all metals without staining, also when kept at the correct concentration (check with refractometer) doesn't get everything "gummy" like some others.
Although a bit pricey for 5 gal., $110.00, it will make almost 90 gal. of coolant. Good luck. |