Weird cooling system behaviour

I thought I'd update and conclude this thread as often threads are left open ended and when searching you don't quite get answers...

So the symptoms were:

Not reaching above 130F

No real heat to speak of thru vents.

After turning the car off within about 5 minutes steam and dirty coolant would start spuwing out of the overflow hose and all over the street.

The first inspection of the system revealed the radiator was leaking and I assumed the Tstat was stuck open.

I sourced a replacement radiator from a stick vehicle and fitted an external oil cooler for the transmission. Both get excellent cooling from the electric fan fitted on the grille side of the radiator.

While I was changing the rad I obviously removed the Tstat housing: Empty! No Tstat, obvious reason for lack of proper temp (especially with the weather in the mid 20's)

Flushed the intere system with a garden hose with the car parked above a storm drain (90% of coolant was already drained) the storm drain thing was an excellent tip I got from a fellow city backyard mechanic, just point the lower rad hose at the drain and presto. Did this with the engine running and without untill the system was fully clear.

The main culprit was the radiator and cap. Being as leaky as it was and full of holes it was suckin in air and creating pockets of air which created the blow off after the car was turned off. The coolant didn't get warm enough but the trapped air sure did and found it's way out thru the overflow line and some leaks in the rad, result: coolant everywhere.

Installed new (to me) rad and brand new oil cooler, new 180* Tstat and gasket with origional housing, had to use silicon gasket to get it all to seal properly, finally new 1 bar rad cap. Cut the lines from the trans and mounted the cooler engine side and hooked them up using hose and clamps (wouldn't work on the other side with the electric fan) and I"m happy with the result. The flow is good and cooling is excellent.

Hoses and all are fine and so far on the one testdrive I've been on all is great. It did take quite a while to get up to temp but is very cold out, let it idle aprox 10 min still not above 140*, drove around for a few miles, not much change, let her sit at idle about 5 min later nice and healthy needle in the middle of the range on the stock meter and a big smile on my face, electric fan kicked on like it should and all seems well, heater core stopped leaking and coolant is a normal colour (slightly brown but that's not surprising).

Thanks greatly to all who chimed in, it was straight forward and easy enough to solve just that the symptoms were a bit strange at first.

David