I own a 1948 F1 with a flathead V8 engine. Lately, when I start the truck to
let it warm up while idling (my typical once a week winter pattern) there is a
small amount of coolant (maybe a tablespoon or so) on the ground and frame on
the driver side. This occurs only during start-up and, at least for now, there
has been no coolant on the ground when the engine is running during warm-up or
after I turn it off. I have tightened the upper and lower radiator hoses but
that hasn't solved the problem.

Could this be a water pump going bad? If so, how come there is no loss of
coolant while the engine is under pressure while warming up and idling? Or
could it be a small hole on the under side of the driver side lower radiator
hose? If that were the case, wouldn't I also lose coolant during warm-up?

BTW, the lower radiator hoses on my truck are straight and not bent or curved
like the picture of the replacement hoses shown in my Sacramento Vintage Ford
catalog. Are my hoses incorrect?

I'm no mechanic and while I have found a shop who will replace the water pumps
with ones I bring to them (in other words, they have no problem if I, rather
than they, order the parts) I don't want to shell out $150 for two pumps if the
problem lies elsewhere. Thanks!

 

Try placing a piece of clean paper close under each place you suspect the leak may be occurring. You may have to tape the papers in place.

 

The chance is good you have a leak developing in the one waterpump. It's pretty common, just like a modern engine. Eventually the seals let coolant get past. If you decide to pull it off, remember it is also the motor mount. A block of wood under the oil pan will cushion the jack. Just take it up enough to give you a bit of clearance.

Also, don't forget the 9/16" bolt inside the lower hose pipe. Use a 6 point socket and you can usually get them out easily.

Your rad hoses should be straight. I haven't looked at the Sac Vintage catalog, but it probably shows a universal one-piece flexible hose. Originally the top hose should have a curved metal pipe that is connected to both the radiator and the t-stat housing by a short section of hose on each end.

The bottom hoses are short and straight and hard to install. Unless your current hose is new, replace it if and when you replace the pump. I push the hose on the radiator first, then push/pull/fold as necessary to get it to slide over the wp snout.

 

When you shut off an engine that has warmed up, the heat in the engine goes entirely into the coolant causing a slightly higher pressure build up. That may be what is making the leak occur somewhere. The best way to detect the leak is with a pressure tester. It attaches where the radiator cap goes and you pump up the pressure, say to 7-10 pounds recreating the engine shut down condition. That should enable you to spot the leak in action. Your mechanic's shop should run this test before doing water pump work.