Hey, before you give up, have you checked the error that the MAX31855 returns? Are you sure it's a grounding issue? I determined that by removing one TC from the engine and then getting valid readings from 2 TCs. Then I touched the removed TC to the engine block, and zap! - got the grounding error. Removing the TC, the readings came back on.
OTOH, if your temperature ranges are good for thermistors, I'd not bother with TCs.
Holger