To do a compression test they RECOMMEND that it be at operating temp. One trick is to buy a block heater and let it warm the block, then run the test. Or you can run it cold and the reading will be off a little, but not by much. Make sure when you do it that you pull the plugs out of the rest of the cylinders for the ease of turning it over. Only let the cylinder compress 4 times to get a correct, or almost correct in your case, reading.