The black art of cooling grey motors

[ardiesse]

Richard,

On my "test" motor, I only drilled the small hole out, to 7/16", mostly because I didn't have a 5/8" drill at the time.
On the FC's motor, I drilled both holes out as detailed in the fitting instructions for the gasket.

Even with just the small hole drilled out, the coolant temperature inside the head was lowered 10 degrees C.
Which makes me think that most of the benefit from fitting the modified head gasket comes from blanking off the holes in front of number 1 cylinder.  But drilling out the holes behind number 6 would work as added insurance, if you follow me.

Oh, and the "enlarged rear water ports" applies only to the head gasket compared to a standard one.  Interestingly, the No.1/No.6 water jacket holes in a standard, OEM head gasket (7416667) are 7/16" and 5/8" diameter.

I reckon that you could fit a 7424869 to an unaltered engine and still derive a large benefit from reduced coolant temperatures inside the motor.

Anybody willing to give it a try?  I could even make up a set of Teflon blanks and mail them to an intrepid volunteer.

Rob

P.S. so by 1967 Holden was carrying four different types of red motor head gasket?

[mcl1959]

I think you're right Rob that just fitting the improved head gasket would lower the engine temperature. Enlarging the holes probably provides for a greater flow of water to compensate for the restrictions in other areas. Otherwise the radiator may be being asked to do more than it is capable.
You would like to think that GMH did this test and found that enlarging the rear holes gave better results than not enlarging the rear holes.
Ken

[ardiesse]

Australia Day Update:

I put a 160 deg. F thermostat in the cooling system and followed maco's advice to drill a couple of 1/8" holes in the thermostat body.  Took the car for a cruise out along Mona Vale Road.  At a servo at Newport -

Top tank: 63 (i.e. ambient + 40)
Bottom Tank: 47 (i.e. ambient + 25)
Rear cyl head: 71
Front cyl head: 73

160 F is 69 C, so the thermostat's regulating the temperature perfectly.  The servo at Newport is at the bottom of a long downhill run on Barrenjoey Rd, which would be why the bottom radiator tank temperature is so low.

One unintended consequence of getting the radiator cleaned out - a very slow weep has started from one of the tubes.  Maybe it'll seal itself with calcium deposits over time . . .

Rob