So I just recently changed the oil on my recently bought 1987 Mustang LX. The previous owner told me to use 20/50 Racing and the only one I could find at autozone for 20/50 racing was Valvoline 20W-50 VR1 Racing Oil. Drained both parts of the oil down low, then put in 4 and 1/2 into the top till I got home and put the rest in to make 5 quarts. Now the tempeture reading is starting to fluctuate a lot, and sometimes goes to the red which is 270 degrees. I'm not sure if this is the actual reading or if the thermostat is acting up. Also, when I pop the hood after driving and receiving these high tempetures, I can hear a soft sound like air is leaking somewhere, like a pssstttt. Not sure if this is something I could have caused from the oil change or if this is a whole new problem all together. Any information you guys can give me would be great.