[Bob Carriere]

When you're hot you are hot.

How can you tell if it is the engine that is being overheated by a plugged passageway or the radiator that is not flowing in all tubes.

I would try to test the radiator with a known temperature water going in and measure the delta.... actual drop in water temp..... and by this I mean off the engine completely...... but may be cheaper to run it to the rad shop to have it boiled out and the tubes rodded which means taking(unsoldering) the top and bottom tank off.

On the engine...... without taking the engine apart.... would it be possible to remove the water pump, all frost plugs, temp sensor and drain petcock and flush and fish in there with a coat hanger and/or pressure washer until all that flows out is clear...?

How worn out are the impeller blades on your water pump..... I have seen even rebuilt pumps with very eroded impeller blades.

Can the engine be run with no rad but with a garden hose with controlled flow X amount of water volume and measure water temp going in and going out at various RPM...... hard to simulate load on the engine without some braking device on the output shaft......

On the other issue raised by Alex...... in the Chev parts manual dated Jan 1941 they list the cowl as a separate part from the ARCH BARS...... and the cowl is common to all sizes of cab11/12...... on the other hand they also list the ARCH BARS right and left ( confusing because to us restorer they are all the same once welded to the cowl angle iron) and shows that the arch bars are all the same part number for RH and LH for all C15, 15a,30, etc. size trucks....BUT the C8 has a separate part number which would reflect it own peculiar BAR shape due to the different frame, steering configuration, etc.

I have two sets of C15a spare arches at the barn ....... I could not find any numbering on them at all.... mind you all are rusty.

Phil .....US radiator makes an aluminium rad that is a copy of the cab 12 and includes the off set 90 degree filler tube.... only issue with the AL rad is you will need special coolant compatible with AL...... U tube has a few clips on their manufacturing process and they sell regularly on EBay.

Good luck.

Bob C