I think what they are meaning is that the L31 Vortec heads do have the same coolant passages as the '55-'95 heads with the exception of the thermostat bypass hole. Thus the need for an external bypass. I brought this up here on this forum nearly 6 years ago and the general consensus was that it did not matter as long as a heater core was plumbed into the cooling system.
Quote:
Originally Posted by andyh1956
So the text of the GM tutorial is to plumb the cooling system like a BB or a Ford.
Strange that in the text of the 350 HO engine on sheet 2 while talking cyl heads it says " The water passages are the same as the original 1955 small block design."
Then on sheet 4 "Any small block engine, regardless of year, that uses Vortec heads, will require an external coolant bypass line from the intake manifold to the 5/8" hose nipple on the water pump (passenger’s side). Suggested routing is from the 3/8 NPSF boss on intake manifold to the water pump."
Go figure.
Anyway I have a 350 Ramjet down in the shop with a std rotation long water pump on it sitting on a motor stand. It uses Vortec heads. In the morning I will go look at it & see if it has bypassed cooling & report back.
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