It is very handy to use the laser to check, sometimes you need to turn off the engine so air flow does not affect where you are measuring. I like to monitor the oil temp at the filter, as that is what is going into the engine and relates to the viscosity that will be flowing to the bearings, but on my Mini I put the sensor in the transmission. On my Corvair, which is air cooled, the temp sensor is on the oil flow out of the filter. After a hard run up the mountain to work I can get the temp (laser measured) up to 106ºC on a 40ºC day.

On my Grand Cherokees (previous and current) I can watch the temps on the dash. Oil is normally 5ºC to 10ºC below water temp, and it has an oil cooler with water from the radiator that opens at certain temps. As I push a hard mountain climb a full load in 40ºC weather, I can see the water temperature hit as much as 106ºC, but during the last 5º of that, the oil temp catches up to the water temp. Then, as I go down the other side, the water temp lowers faster than the oil temp.

The head is always the hottest part of the engine, as it gets direct heat from the burning of the gasoline. Very little oil flows through there, but a lot of water. Note that some cars now have two thermostats to regulate more coolant flow through the head than the block, trying to reduce problems of expansion and contraction that cause head gasket failure.

When I check temps of race cars at the end of the run, oil temps at the filter are often around 120ºC while coolant temps are 125ºC (held from boiling from the glycol in the coolant and the pressurized cap).

It is good to use the laser to check for gauge problems, measuring where the sensor is, or for finding blocked parts of your radiator. On engines with individual heads, you can check efficiency of burn by checking the head temps.