I finally get around to swapping my dual quad manifold onto my '61 389 Pontiac. Low and behold, its the wrong ass manifold. That is to say, its not a bolt for bolt swap. The original manifold/waterpump has a water passage sealed with an o ring. The Offy Dual Quad has no such animal. There are the same provisions for heater hose and Temp sensor. Here's where it gets interesting. The part number, 5162 appears to be used on 2 separate configurations: one has the thermostat housing on the top and the correct water passage. The one I have has thermostat housing on the front and no water passage. No reminders about what an idiot I am, I've figured that out for myself. What I would like to know is, year what does the Offy really fit? Can it be made to work with the existing Water pump? Help a poor ADHD afflicted brother out.
Got pictures of the port surfaces? The Casting number on the blue manifold shows it's for a '62 389, maybe that was the first year for that bypass feature? Did stock '61 manifolds have it? Maybe you're looking at a 1 year only Offy part made in late '60 or early '61 before that bypass appeared. Very strange. Most listings show '61-'64 as being the same. I have an early dual quad manifold out in the shop, I'll look at it tomorrow. Now you have me wondering too.
yours is the correct piece for the years .. the water neck is a special piece and has a bypass channel in it ( so it would warm up faster and not blow out the thermostat also so you could bypass heater core ) Offy #5028A and is still available ( have to search for it ) , and you plug the bypass on the back of the pump by threading it and using a 3/8 npt plug . some of the manifolds ( early units ) had a slot machined from the the bypass near the thermostat to the neck area and a plate covered it and then the stock neck went over it , but the plate was prone to leaking and the thermostat would move around as it wasn't held tight .
Well what do you know, Offy had a better plan. I was going to suggest drilling the thermostat or leaving it out and plugging the back of the pump but the OP is up in the often much colder north where as I'm down here in the heat.
like he said there is 2 versions of this manifold ( actually 3 because of the milled slot /plate version which was a one or two year deal and marketed as a 425A piece ) , the older ones are like this , the but the later ones they moved to the top like the post 65 manifolds . only reason I know this is I ran across this years back when doing my buddys GP , what ticked me off was the catalog does not mention you need the special neck and it was not included with the manifold , the neck was $35 bucks back in the 80's it turned a simple several hour job into a several week job waiting for the neck to come from CA .
The bypass is factory issue for '61 too. The only Offy manifold (same PN) with the bypass has the water neck on the top. Guess it comes down to name yer poison! Different manifold, or plug the pump housing. The good and bad news is, I have the correct waterneck for the wrong manifold
if your careful with the cover threading it can be reused later with the OEm style bypass ( I have threaded the cover on the block by putting the plug on the inside of the pump housing , use a aluminum allen head plug from earls ) , and the offy manifold should help lower the water temp from not recycling the hot manifold water back thru pump to the cooled water from the radiator
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