Lower half of radiator stays cold while driving

[bavArian]

Hello everyone,

I took my A for a few trips in the last few days and, while it runs well now, I still have a problem with an overheating engine when driving uphill for extended periods of time or going faster than ~ 45 - 50 mph. (at an ambient temp. of ~70 °F)


First off some info:

- ran 50/50 water/antifreeze
- switched to straight water with diswasher tabs today
- timing was checked with a timing light, it's spot on; manual advance works
- no bubbles in the water with the engine running, just a constant stream of water from the pump
- carb is fine now, jets are within specs


What I noticed is that immediately after stopping when the car starts to overheat, the upper half of the radiator is hot but the lower half is relatively cool. It only gets hot 30 seconds (or more) after stopping.
I understand that the water should exit the rad cooler than it enters it (duh) but is it normal for the water to cool down so much? It seems to me that the heat transfer from the water to the rad is considerably worse in the lower half of the radiator. Idiot-me didn't think to check if the outlet of the rad is hot or cold, will do that on the next run.


I took it on a trip of about 30 mls today with the diswasher tabs in it and then emptied the rad. The water had a yellow/brownish hue and didn't look clean. I assume that's just dirt/grease from the past that's slowly being dissolved by the hot water?
Might add that the antifreeze-mixture that I ran previously had the same color.


Is there anything else I can do without removing the rad and backflushing it with a pump? Or should I just go for a few trips and change the water in between to see if it gets better?

Thanks,


Daniel