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Radiator PRESSURE CAP and Interchange Parts List - CO-126

ARH1022 Cap [4-psi] for radiator block [1500 + early Twin Cam + early 1600]
ARH1039 Cap [7-psi] Com. (C) 71832 - [mid 1600]- Always supply AEH1542
AEH1542 Cap [7-psi] Com, (C) 88192 - [late 1600 + 1622] - retrofit to all MGA

pressure cap bottom side pressure cap bottom side
pressure cap drawing Original radiator pressure cap for MGA has 1-1/8-inch reach to fit 1-inch deep filler neck. I like to call this the "long reach cap" for the "deep filler neck". The MGB and other later model cars commonly have a shorter filler neck requiring a 7/8-inch reach cap for 3/4-inch deep filler neck. Please do not confuse these different configurations. The long reach cap cannot be installed in the shallow (3/4" deep) filler neck. If you install a short reach cap in the deeper (1" deep) filler neck it will not hold pressure, same as having no cap at all.

Please review article CO-101 on Keeping your cool", and article CO-204 on Coolant recovery system". Early production MGA pressure cap had 4-psi relief pressure rating. In July 1959 at Car Number 71832 this was changed to 7-psi, and it is highly recommended that earlier cars should be retrofit with the 7-psi cap. This should not deduct points in a concours car show, as it is to be considered original by the factory design change and Confidential Service Memorandum CSM_MG/289 noting the upgrade to earlier cars.

pressure cap bottom side At the inside top of the pressure cap there is a wide flange, actually a springy diaphragm, that covers the top of the filler neck. This generally prevents fluid from spilling over the top of the neck and directs the fluid to flow out through a small pipe on the side of the filler neck. That pipe is originally routed to a point low on the side of the radiator where any escaping fluid can drain on the ground. The diaphragm in the top of the pressure cap does not (originally) have to be absolutely pressure tight, just good enough to direct most of the overflow into the drain tube, and not allow much fluid to dribble out the top of the filler neck. As such, the original cap design used a bare metal diaphragm with metal to metal contact between the diaphragm and the top of the filler neck.

coolant recovery cap For the purpose of installing the coolant recovery system, the pressure cap DOES need to have an absolute seal at the top of the filler neck, because it has to be able to create a slight vacuum to draw fluid back into the radiator when the system cools down. You will notice in the picture above that the top diaphragm in the cap has a thin rubber seal around the edge. This is not included on the original MGA radiator cap. It was not used much prior to 1968 (when radiators had shorter necks), so the demand is only for aftermarket conversions on older cars.

The radiator cap in this picture is the long reach cap with the top seal, one of those very rare items. This one is NAPA-Balkamp part number 703-1411, but ordering this part number does not guarantee that you will get what you need. In past years this same part number was used for the original type cap with no rubber seal at the top. Around 2001 or (thereabout) the cap design was changed to include the top seal. Since the new design works equally well in older applications, the new part supersedes the old one, and the same part number is still used. With demand being so low, and sales slow, it is possible that there may still be some of the older parts still in stock on the shelves for years to come. As recently as summer 2003 my local NAPA dealer had an older part on the shelf in Illinois, while a friend found this newer one for me at a NAPA dealer in North Carolina. So if you're buying one of these parts, open the box and check it before you walk out of the store.

Stant pressure cap Stant pressure cap Stant pressure cap Stant pressure cap
Stant 10206 recovery type long reach cap with top seal

Pressure caps, 7-psi with 1-inch reach, as pictured above that will work for coolant recovery:
ManufacturerPart No.
Balkamp 7031411
Mini Spares GRC101 (same as NTG part)
Motorad (Taiwan)T-6   (UPC 055644000060)
NAPA 703-1411
NTG B350A
Stant (Mexico) 10206   (UPC 00333420010602)
Summit Racing SNN-10206   (Stant)
Check Amazon and Ebay for the good part numbers.

NTG pressure cap NTG pressure cap NTG pressure cap
NTG part number B350A coolant recovery cap appears to be a standard pressure cap with a thin rubber washer added and left loose (not bonded). Otherwise it appears to be original style in all respects, including original stamping of the lettering on top.

Pressure caps, 7-psi with 1-inch reach that will NOT work for coolant recovery:
(This list could ultimately get to be very long).
ManufacturerPart No.
Stant R-6

Cross reference numbers for the MOTORAD T-6 and STANT 10206 pressure caps. Check to be sure if these will or will not have the top seal to work for coolant recovery.
ManufacturerPart No.
ACDelco Aftermarket 12R31
ACDelco Aftermarket RC-3
Badger BR-6
Beck Arnley 133-801
Berkson P-6
BMC-Rover GRC101
Borg & Beck FRC 64
Bowes 77-505
Bowes 7BC-6
Bowes 7BC-6
Bradex TCL7
CarQuest 33003
Dole DR-6
Eaton Corp. ER-6
Firstline FRC 64
Ford 240E 8100 A
Ford 240E 8100 A1
Ford 240E 8100 A2
Ford 240E 8100 A3
Ford 1506245
Ford 1508306
Ford 1515128
Ford 1517588
Ford 1517589
Ford 1519321
Ford 1521874
Ford A710X 8100 AJA
Ford A710X 8100 BA
Ford A710X 8100 HA
Ford A710X 8100 NA
Ford B2AZ 8100 E
Gates 31306
Gates 33003
Gates 7031411
Gates RAD6
Gates, Canada 31306
ManufacturerPart No.
General Motors 255300
General Motors 850797
Ideal Aftermarket 46004
John Deere AT29054
Lazorlite U95-4128
Lucas KRB211
Lucas LC3
Lucas LC3
MGOC GRC101
Moss Europe GRC101
Moss USA 583-004
Motaquip VCR207
Motorcraft RS-6
Motorcraft ERS 6
Motorcraft ERS 11
Murray Temp. Control  M-6
MQ VCR207
Powertrain PCRC7L
Purolator RC-6
Robertshaw RR-6
Rover Group ARH1039
Rover Group ARH1542
Rover Group ARH1662
Talbot 1-221-765
Talbot K21765
Unipart GRC101
Vera 53-10629
Victoria British 2-301
Wayne WA-6
Wayne WC-6
Wayne WR-6
Wipac S5300

Vehicles this part fits: Make Model Engine Year Austin A60 1962-1964 Austin Cambridge 1962-1964 Austin Mini 1960-1964 Austin Princess 1962-1964 Austin Westminster 1960-1961 Auston Healey Sprite 1958-1970 Austin Healey 100-6 1958-1959 Austin Healey 3000 1959-1967 Buick Roadmaster 1942-1947 Daimler SP250 1960-1963 Fiat 850 1969-1970 Fiat Strada 1979-1981 Ford Anglia 1962-1966 Ford Anglia II 1.0 1959-1964 Ford Capri 1962-1963 Ford Consul 1960-1963 Ford Cortina 1963-1965 Ford Country Sedan 1952 Ford Crestline 1952 Ford Customline 1952 Ford Prefect 1.0 1959-1961 Ford Victoria 1952 Ford Zephyr 1960-1961 Hudson Commodore Series 1950-1952 Hudson Hornet 1951-1953 Hudson Pacemaker 1951-1952 Hudson Super Custom 1951 Hudson Super Jet 1953 Hudson Super Series 195 Hudson Super Wasp 1953 Hudson Wasp 1952-1953 Mercury Monterey 1951-1953 MG MGA 1955-1962 MG MGB 1963-1964 MG Magnette 1963 MG Midget 1963-1964 Morris Minor 1960-1966 Packard Deluxe Eight 1948-1950 Packard Standard Eight 1948-1950 Packard Super Deluxe Eight 1949-1950 Packard Super Eight 1948-1950 Rover Group (Austin) AH Sprite II 1.1 1960-1962 Rover Group (Austin) AH Sprite III 1.1 1963-1966 Rover Group (Austin) AH Sprite IV 1.3 1966-1974 Rover Group (Austin) Mini 848cc 1961-1969 Rover Group (MG) MG Magnette 1.6 1961-1968 Rover Group (MG) MG Midget 1.1 1961-1966 Rover Group (MG) MG Midget 1.3 1966-1974 Rover Group (MG) MG Midget 1.5 1974-1980 Rover Group (MG) MGA 1600 1955-1962 Rover Group (Morris) Oxford 1.6 1962-1970 Rover Group (Riley) Elf 848cc 1959-1969 Rover Group (Wolseley) Hornet 848cc 1959-1962 Skoda 105 1.0 1976-1989 Skoda 120 1.2 1976-1989 Skoda 130 1.3 1984-1989 Studebaker Champion 1952-1955 Studebaker Commander 1952-1955 Studebaker Truck E5, E7, E10, E1 1955-1960 Sunbeam Alpine 1960-1967

Addendum November 23, 2016:
The long neck recovery type pressure cap is Motorad T-6 or NAPA 703-1411 or Stant 10206. I have been trying to cross reference this to other suppliers but always end up with non-recovery type caps, because the original applications were non-recovery type. Some years ago Motorad and NAPA and Stant upgraded this part number cap to be recovery type but apparently no one else has. Nearly every NAPA store has one in stock. It is possible that Motorad or Stant may make it for other suppliers, but I haven't found them yet. Check Amazon and Ebay for the good part numbers.

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