|The MGA With An Attitude|
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
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.
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.
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:
Pressure caps, 7-psi with 1-inch reach that will NOT work for coolant recovery:
(This list could ultimately get to be very long).
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.
|ACDelco Aftermarket ||12R31|
|ACDelco Aftermarket ||RC-3|
|Beck Arnley ||133-801|
|Borg & Beck ||FRC 64|
|Eaton Corp. ||ER-6|
|Firstline ||FRC 64|
|Ford ||240E 8100 A|
|Ford ||240E 8100 A1|
|Ford ||240E 8100 A2|
|Ford ||240E 8100 A3|
|Ford ||A710X 8100 AJA|
|Ford ||A710X 8100 BA|
|Ford ||A710X 8100 HA|
|Ford ||A710X 8100 NA|
|Ford ||B2AZ 8100 E|
|Gates, Canada ||31306||
|General Motors ||255300|
|General Motors ||850797|
|Ideal Aftermarket ||46004|
|John Deere ||AT29054|
|Moss Europe ||GRC101|
|Moss USA ||583-004|
|Motorcraft ||ERS 6|
|Motorcraft ||ERS 11|
|Murray Temp. Control ||M-6|
|Rover Group ||ARH1039|
|Rover Group ||ARH1542|
|Rover Group ||ARH1662|
|Victoria British ||2-301|
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
Addendum November 23, 2016:
The long neck recovery type pressure cap is NAPA part number 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 NAPA (or Stant) upgraded this part number cap to be recovery type but apparently no one else has. So far I have not found any other source for this part, but nearly every NAPA store has one in stock. It is possible that Stant may make it for other suppliers, but I haven't found them yet. Maybe some other retailers could source the Stant part for you.