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Posted by Clint Dixon [74.206.63.42] on Tuesday, November 20, 2012 at 14:15:04 :
I was changing out the summer thermostat to a winter one in my ’51 B3PW today to allow quicker warm-ups for snowplowing. I got to thinking about the thermostat discussions that we had here on the Forum a while back. This prompted me to look more closely at my parts.
The 922 834 Cylinder Water Outlet Elbow on my ’51 has a small hole drilled into the casting that allows for a slight bypass of the thermostat. This hole is just large enough to pass a #43 drill bit through. I have seen this hole before and have always kept it clean, but never gave it much more thought. I checked a spare 922 834 elbow I have and, sure enough, it too has the hole.
This hole can be seen in the image where I have a wire sticking through it in both the spare elbow (top view) and the elbow from my ’51 (middle view). The middle view shows the elbow clamped in a vice inverted 180 degrees from how it mounts to the head of the engine. In the bottom view is a correct thermostat. The red arrows indicate where the thermostat seals to the elbow with a thick rubber washer. This seal keeps coolant in the engine, and being recirculated by the water pump until the thermostat opens. The large horizontal slots in the thermostat (there four around the parameter) are where recirculated coolant flows through the by-pass hose to the water pump.
I believe this hole in the cast elbow may be what Vintage Power Wagons is trying to duplicate by recommending that customers drill a 1/32” hole in the plunger of the thermostat. Though, I still do not know what the point of doing so is since a machined hole already exists in the elbow itself.
Elbow 922 834 was used from 1946 through engine number T137-21560 in 1951 according to the parts lists. This was also when the cylinder head, water pump, and the thermostat all changed. I have not owned a truck with the newer head, but I believe a “hump” was added to the front of the head allowing internal by-pass to the water pump – allowing deletion of the external nipple on the elbow, bypass hose, and bolt on elbow to the water pump.
The new elbow (#1327 124) was used from engine number T137-21560 to serial number 83931055 when it was replaced by elbow number 853 969. This lasted through serial number 83947778 when it was replaced by elbow number 1406 151. This was used up until the introduction of the 251 engine on 1961 WM300 model trucks. These engines used elbow 1142 442. These different elbows are not all shown in the VPW catalog or PDF file. They may be recommending the 1/32 hole be drilled to allow for a missmatch of parts or an incorrect thermostat being used.
I remain unconvinced that any additional holes need to be drilled when using the correct thermostat and accompanying parts that were designed for a particular engine and model of truck.
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