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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 recoverycap 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.

Pressure caps, 7-psi with 1-inch reach, as pictured above that will work for coolant recovery:
ManufacturerPart No.
NAPA/Balkamp 703-1411
Stant 10206

Cross reference numbers for the STANT 10206 pressure cap. 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, 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 Auston Healey Sprite MK-I Ford Anglia II 1.0 1959-1964 Ford Prefect 1.0 1959-1961 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 1960-1962 Retrofit to all earlier models 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

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