250 6cyl overheating

I have a 1963 Chevy II with an overheating problem. I have replaced the thermostat (180) , all hoses, new radiator, timing set at 4 degrees before, tuned up, and flushed and reverse flushed.....runs hot if riding at a steady 50-55mph (it starts to climb to 200) also if sitting in traffic.
Does anyone know of a product or technique that I could use to possibly flush it out better?
Thanks

 

sounds like a head gasket.

 

Sounds like a problem I had with my 250 in my '62 Chevy II. Make sure that your vacuum advance is connected to manifold vacuum and not ported vacuum. That one little thing helped me out immenesly...

 

Give us some specifics regarding the fan set up, and post a few pictures if you can. This will help diagnose tremendously. Also, while it is at running temperature, feel around the radiator with your hand- CAREFULLY- and feel for even distribution of heat. If you find a area that is cooler than others, we have found one of the problems.

 

It has a flex-fan (5 blade). I pointed digital temp gun at all spots on radiator and all were the same temp.

 

I would probably go with the water pump, pull the radiator cap, and let the engine fully warm up to running temp. Watch the flow of coolant in the radiator, see how fast or slow the movement of the coolant is moving. I replaced the pump on my 230, solved the overheat problem for me.

 

200 is not overheating or to hot.

 

Ditto

 

You changed everything but the waterpump. Are you having to add water/coolant regularly or not ? With the flex fan do you run a shroud or not ?

 

Bingo. 50/50 Antifreeze doesn't boil until 260 deg. F with a 16 psi cap. Remember, the boiling point of the coolant goes up 3 deg. for every pound of pressure in the system. There is nothing wrong with running at 200.

 

If the flex fan is an aftermarket piece, and you still have a stock fan blade available, I'd try switching back to the stock fan blade and see if there's any improvement. Should be easy to make the swap and flex fans can be notorious for not moving as much air as the stock fan.

 

Put that flex fan in the junk pile. They kill! I had one louvre the hood of my truck. They're notoriuos for flying apart.
Put a stock fan on. Bump your timing up to 12 degrees. Check your bottom rad hose for a coil. It can collapse, pump cavitates and no coolant flow.