The Ford Barn

Stephen Cash · 05-17-2025, 08:21 PM

Can somebody please tell me what radiator cap pressure to use after installation of a new style radiator on a 21 stud flathead engine? Thanks

aussie merc · 05-17-2025, 08:32 PM

No more than 7 psi its not the rad its everything else [head gaskets heater etc] 4 psi works well and doesnt stress anything

19Fordy · 05-19-2025, 08:37 AM

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Keep in mind the higher the psi, the more stress on the rubber hoses.

05-17-2025, 08:21 PM	#1
Stephen Cash Junior Member Join Date: Jan 2025 Posts: 1	Radiator cap pressure after installation of a new Johnson radiator with flathead eng Can somebody please tell me what radiator cap pressure to use after installation of a new style radiator on a 21 stud flathead engine? Thanks

05-17-2025, 08:32 PM	#2
aussie merc Senior Member Join Date: Sep 2016 Location: sydney australia Posts: 1,125	Re: Radiator cap pressure after installation of a new Johnson radiator with flathead No more than 7 psi its not the rad its everything else [head gaskets heater etc] 4 psi works well and doesnt stress anything

05-19-2025, 08:37 AM	#3
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 11,605	Re: Radiator cap pressure after installation of a new Johnson radiator with flathead Sponsored Links (Register now to hide all advertisements) Keep in mind the higher the psi, the more stress on the rubber hoses.