i had a small leak in the radiator the other day. today i bought some stop leak and put a lil bit in the radiator,not the whole bottle just a lil,not even a qtr. of the bottle and on my way home the temp. gauge shot all the way up close to the red line,but when i got off the highway and started slowing down,the gauge fell. it pretty much was going up and down the rest of the way...any advice or suggestions?