89 civic lx sedan automatic

just bought the car. at a stop, the temp rises, then as you drive off, the temp rises a little more, then comes back down. also at a stop, the temp rises, then i put the car in neutral, then rev the motor, the temp comes back down. also when driving the temp rises to a little over half, then comes back down on its own. so i figure it was a thermostat, so i replaced it today with a cooler temp one, now the temp is good at idle, but when its driving it wants to overheat way worse than before. theres no leaks anywhere, the car doesnt smoke at all, the oil is dark brown, the heater gets warm/hot about 5 minutes AFTER the car is at normal operating temp. i think theres a clog in the radiator because when i drained the coolant today, it was brown. have any of you tried that kit you can buy from autozone that hooks up to your heater lines and you hook a garden hose up to it a flush it out? what about ultrasonic cleaning? im REALLY short on cash right now and i need my car running, so the cheapest route would be the kit from autozone, then the ultrasonic cleaning, then lastly, buying a new radiator. what do you all think? think its the radiator? please give me all your relavant input. thanks.

 

yeah the cheapest route would be the kit from autozone. btw the last time my old DA did that, it was a few weeks later that I blew my head gasket. it's not that I'm saying your head gasket will blow but I'd give the engine at least a compression test before you start wasting money changing parts you don't need to. just my .02

 

man you need a head gasket .you need to fix it soon or start looking for a new motor good luck