Ok, so here's the situation - I recently had a 354 Hemi built for my coupe. It's good to go and pretty dialed in. I had Walker sort me out with one of their Cobra radiators; pretty much the best I could afford. Walker recommended a 16 lb radiator cap. I wanted the engine to look right, so I got a rebuilt, stock water pump from Kanter. After a few days that water pump started to leak. Needless to say, I was pretty disappointed and sent it back to Kanter for a rebuild on their dime. In the meantime I took my original water pump and rebuilt it with a kit from Ebay https://r.tapatalk.com/shareLink/to...&share_fid=11843&share_type=t&link_source=app 354 Hemi water pump rebuild Well, today (I work out of town and haven't had a chance to drive the car much) I was driving and dammit, the water pump started to leak! I was talking to my brother later (meanwhile, the leak stopped after I shut the car off at home) and we got talking about why this would happen. So, in 1956 a stock 364 Hemi radiator cap was 7 lbs. Is it possible I'm creating too much pressure and overpowering the stock style seals in my water pump? Sent from my SM-G950U using The H.A.M.B. mobile app
Ok, I'm going to grab a 7 lb cap in the morning and give it a try. Fingers crossed I haven't ruined the seals already! Sent from my SM-G950U using The H.A.M.B. mobile app
I’m running a 16 # cap with a stock water pump that I purchased off eBay. They are all new castings and parts. I have had no problems! Rich
The best way to determine an answer I would say is to pressure test the cooling system and determine if it leaks , where and what pressure it starts . The only reason to run a sixteen lb cap is it raises the boiling point of the water or coolant . If it’s not getting near boiling temp , then the 7 lb will be good to go . I hate to say this but I think you may experiencing a leaking head gasket issue . Does the cooling system hold pressure for a long time after shutdown ? This is a tale-tail sign of head gasket issue .
I'm pretty much positive that there are no issues with the head gaskets. None of the tell-tale signs (and for what it's worth, the radiator pressure drops off pretty quick when the engine is shut down) Sent from my SM-G950U using The H.A.M.B. mobile app
If it don't overheat, you can run no pressure if the rad cools well. The most I run is 7 lbs, never have a cooling problem, you don't need 16 lbs, my guess is the pump can't take that much pressure.
Can you post a link to where you found new castings of 354 Hemi water pumps, please. I wasn't able to find anything new - I'd probably grab a new pump rather than keep rebuilding old ones. Sent from my SM-G950U using The H.A.M.B. mobile app
https://www.m.ebay.com/itm/17306854...sid=p2385738.m4383.l4068.c10&boolp=1&nrd=true I’m running the early water pump assembly which is for the 331 which may be different than yours. They also carry the 392 . Mine was a truck engine and came with the high mount water pump which I Converted to the early style. I had problems with rebuilt pumps also. As far as the pressure cap goes it will only see that High pressure if it over heats. It’s all I can do to get it to maintain 165 with a 180 stat.
I quit running pressure in my radiators years ago.. I have a hole punched into my radiator cap and use a quart sized overflow bottle.. I never had any issues and I sware the engine runs better without pressure.. I would open up one of the caps and hide a overflow bottle.. I have also done this without an overflow bottle and had no issues but figure its best to keep the system air tight..
With a pressurized radiator it raises the boiling point of the coolant by 3 degrees for every 1 pound of cap pressure in the system. So with a 7 pound cap your radiator would have to get to 233 degrees before the 7 pound cap would blow.
The water pump does create some pressure in the system..The pressure is necessary in many engines to prevent steam bubbles that impair cooling.The engine can be 180 degrees and still have quite a bit of pressure because of the this....Of course this varies from engine to engine and how the vehicle is driven.
Well, I put a 7lb cap on it and drove it pretty hard yesterday and had zero leaks... Sent from my SM-G950U using The H.A.M.B. mobile app
I run a ZERO lb cap in my '56 New Yorker, and use a coolant recovery bottle. Never have overheated it even in 100 degree Kansas heat. Stock radiator, stock shroud, stock mechanical fan, 50/50 ethylene glycol coolant.
I am not probably going to say anything relevant here but I have a tendency to run what was originally run with the specific engine I am using. Like @Ebbspeed I like a catch can and that usually involves using a lighter cap. I do one thing that lots of HAMBers and Hot Rodders in general do not do. I do not buy my caps off the rack. Yes there was a time that Stant made as good a cap as you could buy and they were very affordable. But that ship has sailed. I spend the extra buck and get the parts guy to earn his keep and get me the premium model.
Hey Beaner… where do you buy a premium cap here locally. Do you remember what brand it was. My O Rielly says Stant is the best there is. (did you buy your Lakewood from a guy in Grain Valley...me)
Stant still works for me.. I really like Stants new line of thermostats, they keep the temp gauge needle almost completely still...
Cap pressure one of main specifications is tank/radiator construction. A lot of early tanks would balloon if pressure was high because of shape. You now see bead rolling,bends etc to add structure. If 16 is recommended, I would stay as close to that as possible.
Like has been mentioned you only need a pressure cap, if you need pressure. When cars first came out there were almost no pressure in the radiators. Then the car manufacturers learned that since the engine was a heat machine it worked better a little hotter.... but then they were gettin real close the the boiling point in parts of the engine! Solution...pressurize the cooling system. How much?? What ever you need. Like mentioned for every 1 psi, it raises the boiling point about 3 degrees. But.... pressurizing the cooling system brought on other problems, mainly more leaks, so they had to make stronger radiators, hoses, etc. So using the lowest pressure cap that solves the problem .... with a little cushion works for me! I always kinda cringed a little seeing 17 psi on a radiator/ cooling system. It’s needed some places, but not all. Bones
The Jalopy Journal
