To Bypass or Not?

[Bob Riding]

Just found this excellent thread.  Water Pumps.  I have a 1950 (P20) 218 engine that came from a local hotrod shop- a young guy in Kerman CA who collect and restores 1950 Plymouth Suburbans. He sold me this motor with a Wilcap adapter that will allow it to bolt up to a GM automatic tranny (I'm using a TH 200 4R) He said it was running and driving great when he had it, but the 218 didn't have enough off-the-line power for him. It has the '53 and later internal bypass thermostat, and straight neck and it looks just like JB Neal's pictures , including a newer NAPA water pump. Am I understanding correctly that even though the new NAPA water pump will work with both pre and post '52 block designs, using the internal type on the older external blocks will lead to warmup and/or operational problems?

[YukonJack]

The page from the service manual you show is only partially correct. P15 Deluxe used the same thermostat housing you have on your motor. Special Deluxe used external by-pass. This had me puzzled for a while. My 47 Deluxe has the same housing you have and a 48 Special Deluxe I had used the external by pass. On page 67 of the shop manual under Cooling System Data if you go to By Pass hose it shows Special Deluxe models only. The plate on the back of the water pump is different also. My Deluxe housing was badly rusted so I picked up a by pass housing and the bypass nipple for the top of the pump. So.....I am running internal by pass and an external housing with the correct thermostat for the housing (big rubber washer that sits on top of the thermostat). I haven't experience any problems.

[Bob Riding]

Thanks for additional detail - I hadn't heard of that on an earlier engine than the P20.I think I will follow your lead.

[Andydodge]

Just to confuse the issue even more..............this engine in the 1941 P11 Plymouth I had was as far as I know the original 1941 engine, the engine number certainly started with P11, however it had an internal bypass thermostat housing as shown and cylinder head with the small bump in between the front of the head and water pump, the water pump went R/s and I replaced it with an Airtex(?) pump with the circular impeller and sealed bearing( which the original pump that was replaced DID have anyway)..........also this engine was supposed to have had a rope rear main seal, yet it had a bolted on neoprene seal.....off course the PO never put those side seals in place .....lol....so it leaked like a sieve.........lol.............Oh...... and thats an Oz only GM Holden single barrel Stromberg carby and a Langdon HEI, both excellent improvements.......lol.......... ...andyd  

[Bob Riding]

Always learning new things I thought I already learned!

 

[greg g]

Both my 46 deluxe and 56 Savoy engines are internal

, But I have seen a 36 with internal, a 47 with external, 39's with either or.  Don't think there was any rhyme or reason for which got what or when.

[Andydodge]

Greg.......agree............methinks it was sorta like............"Hey Fred...what have we got this week? internal or external..........Bill..I've got some of each.........O/k......that'll work".......andyd

[YukonJack]

3 hours ago, greg g said:

Both my 46 deluxe and 56 Savoy engines are internal

, But I have seen a 36 with internal, a 47 with external, 39's with either or.  Don't think there was any rhyme or reason for which got what or when.

That backs up my theory plus the fact that the manual lists a by pass hose for Special Deluxe only. I think after 50 the by pass housing was eliminated.

[Andydodge]

Or maybe Fred & Bill got the sack........or just retired........lol...........andyd

[JBNeal]

When I started fixing up my '48 1/2 ton back in the 80s, I had trouble with engine parts fitting because the reality was that somewhere along the way, my great-grandfather's truck's original 218 was replaced with a '55 Plymouth 230...then Al Gore invented the internet and I was able to do some research to figure out what was going on with the flathead in this not-so-original flathead.  I don't know if the rebuilder did this or the mechanic who installed the engine in the truck, but the 230 has an internal thermostat bypass with the external bypass thermostat housing installed...my guess is that a crated rebuild was installed in the truck, and whatever bolt-on parts were missing from the rebuild were stripped off of the original and slapped on the rebuild...though this 230 also has a Plymouth exhaust manifold...at any rate, I think corn liquor was involved somewhere along the way