"Both of my +4's (race and street) seem to blow water out the top of the radiator. There is then much water loss from the radiator and often  electrical problems (water on the distributor(?) Do you have specific advice on radiator caps for +4's (59-67). It seems the caps are longer
than the standard Stant caps, is this right? Is there a model number for  Stant or other caps? Thanks, Curt"


Bill Fink


There is a longer radiator cap used on +4's - it has a 1.25" neck, and is a Stant R-5 ,4 lbs. Napa # 703-1410.


Bill Fink

John Sheally II

Dear Curt,

Just go to any auto parts shop,I perfer NAPA and ask to see their STANT catalog which list applications and neck size and depth as well as pressures. Application depends on your bore and compression of engine.The type and size of radiator also will influence the cap. On Plus 4s,  I always ran no thermostat in warm weather and a 180 degree in winter for heater use. The cap normally used is 12 to 14 pounds and I like the pressure relief type with the red lift handle. Your radiator will always seek its own level after it is
filled to top and ges through its first heat cycle.  It also varies as to applications and features of the vehicle. Usually, with a stock Plus 4,  it will kick out 1 to 1 and half pints after the first cycle.

Best to you,

John H. Sheally II

Greg Solow

The proper cap for a +4 is a stant R-5.  This is a 1" deep neck 4 #  cap. There is no such thing as a deep neck "recovery cap" unfortunately.  I have tried to have some made but the cost was prohibitive. Using a 7# cap will eventually cause leaks in the radiator.  Using a 7 # cap for short periods of time seems ok.


Greg Solow

John Worrall

If you are blowing water out of your rad it may be a good idea to put an expansion tank on the Bulkhead of the car as do the current Morgan Models...this will at least recirculate the water as well as slightly
increasing the capacity.

John Worrall