Compression leak to cooling system

[Kevin Trent <trentkc@domain.elided>]

Back in V8#990 I described how my Grey Berlina's waterpump seal failed, the 
engine lost coolant and ran the temperature gauge up to the maximum.  I 
replaced the waterpump, flushed the cooling system, put in a 160 degree 
thermostat, torqued the head, changed the oil & spark plugs, and gave it a 
minor tune up.

In the 850 miles since, the car runs OK on 25 mile commutes.  The coolant 
and the oil are not mixing, but the one remaining problem is that I have 
either a bad head gasket or cracked head because I get a steady stream of 
bubbles coming through the radiator and its cap into the overflow 
bottle.  The engine runs cool on short commutes, but if it is run at 
interstate speeds for sustained periods the temperature will creep up above 
normal.   I'm guessing that at high RPM the combustion leak to the coolant 
is "super heating" the coolant resulting in the higher temp reading.

My son and I driving to a bike race this coming weekend that will require a 
3 hour/200 mile interstate trip.  The Berlina is preferred to the GTV, but 
I'm concerned that the compression leak problem described above will 
pressurize the cooling system to the point that I might blow out another 
water pump seal.

Is there be any problem with disabling the pressure seal on the radiator 
cap to avoid pressurizing the cooling system for this trip?  Would it even 
make a difference in reducing the possibility of a seal blowout? Would it 
increase the chances the engine would overheat?

Thanks for any input.   ///kct, Powell, TN
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