FWIW, It probably does not matter that much however the last time I spoke to DMC Joe about this he said a 16 pound cap was best. Mike Subject: RE: [DML] gas and radiator caps... A leak down test with a radiator pressure tool will be the best way to really know. Joseph Vinciguerra (11-110750) Adam, It's best to use the correct radiator cap, which is a 15 pound cap. Both that and the gas cap are available from the DMC vendors for reasonable prices. Mark N VIN 6820 [Non-text portions of this message have been removed]