Hope this is not too stupid a question....

I installed a new radiator because some yobs stole the last one. Tath was nice enough to sell me one and I installed it. I poured in the right mix of antifreeze and water and it sat and idled for 20 minutes, the temp was in the middle range on the gauge the whole time. I went for a drive and all was fine for about 15 minutes then the temp shot up to almost the top of the gauge. I turned the heater on to help lower the temp and because I was on a fen road with no turn-offs to stop on. Then the temp starts fluctuating fom mid range to high about every 3 minutes.

I know I installed the rad correctly, its not a difficult job, and there are no leaks as the system is still full. Is there a bleed point I missed to purge the system of air? The reason I ask is it apears there may be trapped air, thus the fluctuating temps. I have owned more than 40 cars and I have to say this is a first. Evidently there is something I'm missing.

Anyone care to guess? Inputs, as always, are appreciated. Who knows, this may help a fellow muppet out on thier next rad job..... Thanks, Lee

 

Was this a beyond stupid question or has it stumped all the mechanical living legends of the board? Tell me it isn't so.....

 

No bleed point its just a matter of running the car with the header cap off and heater switched to max slowly filling the system as needed,Often needs running for quite along time.(30mins may be even an hour)