OK, Since I stirred up some good discussion about coolant and distilled water in the Mech. Forum, I thought I'd pour some oil on the fire this time. The temp gage on the dash of a car is, of course, the coolant temp gage. I have heard people make the claim here that the engine oil takes longer to reach operating temperature than coolant does. These folks have said you need to wait 10, even 15 minutes into engine operation to get full oil temp. This, frankly, mystifies me. A typical 4 cylinder engine has about 8 quarts of coolant and 4 of oil. OK, some of the coolant is isolated in the radiator until the thermostat opens, maybe half? (Based on the fact that opening my old Saturn's rad drain yielded under 1 gallon of the 2 total in the system) So why would a gallon of coolant circulated through the warming engine gain heat faster than the gallon of oil which has even closer contact with the fastest heating parts of the engine? Seems to me that, being about equivalent in mass, they would heat at the same rate. So why can't I assume that once my coolant reaches 190, my oil is at the same temp (and I can BOOST)? PS No AT fluid temp to worry about - see name.