Ken, would it not be the same to read the bottom of the bolt hole as the tip of the probe? Both are exposed to the water. The probe directly in water and the bolt hole boss is also. There may be a slight air gap under the probe in the hole but this probably wouldn't matter much. JMO.Curiosity question. Would the "Red Ball" Temperature thingee give you temperature of the metal in the block vs give temperature of the water inside the block. Ideally the bottom of the holle where the stud goes has a bottom in it and water cant get to the hole. Inquiring minds want to know. ken