Over heats and will stay running

I got this car for a really good deal. The person from whom I got it from said that it over heats and wont stay on. So I bought a bottle of blue devil. I poured the whole bottle in, but the only problem is that I had to keep starting the car every few minutes the whole fifty minutes that it says it needs to be ran. The car did not want to start afterwards. So I then checked all the fuses to see if any where not good and I found a few of them so I replaced them. I back tracked everything all over again I released the gas pressure from the valve, I was able to get the car started for about five minutes and then it just died. I tried about three or five more times and the car will stay running. Can tell me the what could be the problem?