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Manifold Heat Control Valve page 2
  The following list of heat control valve springs was compiled from several parts catalogs to cover all of the applicable model years.  If you need a spring but are unable to find the correct one; I recommend using what you can find.  As long as the heat valve opens once the engine is hot, a “working” system is better that one that does not function at all.

’33-’36 all...………………………...495828   71/2 coils
’37-’38 all, P/8 1939………………499581   6 coils
P/6 1939, ’40-’50 all, P/6 1951,….502453   31/2 coils
’51 P/8……………………………...516304
’52 P/6……………………………...516177
’52-’54 P/8……………………..…...516303
’53-‘54 P/6 Hydra-Matic..………….517276
‘53-’54 P/6 Synchromesh…………517009

  Pontiac used the large air tube, shown above at the top right, beginning in 1935 on all sixes and eights.  1938 was the final year for use on the six, 1939 for the eight.  They were all fitted with a valve which regulated the amount of airflow, this valve is found in group 3.647, part number 498126.  The tubes are also group 3.647, the individual parts numbers are as follows:

’35-’36   P/8 tube……………………...498124
’35-’36   P/6 tube……………………...498135
‘37-’39   P/8 tube…………………...…499890
’37-’38   P/6 tube…………………...…499891

  My opinion on this air tube is the same as for the spring; if you do not have one, keep looking, but do what you can to allow the heat valve to function!
  Engine wear is at its worst during the warm-up period when the choke is functioning.  No matter how well controlled the choke is; excess gasoline still washes oil off the cylinder walls and gets into the engine oil, causing dilution.  Everything that we can do to minimize choke operation, and get the engine up to normal operating temperature is beneficial.
  Pontiac engineers certainly knew this to be a fact; that is why they spent the time and money to perfect and install these parts; many other manufacturers’ did not, and their cars did not have Pontiacs’ reputation for durability and longevity.   
  You can have your vintage Pontiac tuned to perfection, but if the heat control valve does not work as intended, your car will not perform to perfection.
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This parts breakdown is from the 1941 Pontiac Master Parts Catalog