When a 740 is started from cold and left to idle how long does it take for the system to start to receive pressure, 20 seconds 30 seconds.
If the engine is then stopped after one minute would there be pressure at the pressure cap on the cooling reservoir
The only immediate pressure would be from flow resistance after the pump and very slight. There won't be any real pressure until it reaches boiling temp, however long that takes. Then the pressure is obviously all through the system & should remain until it cools some, much longer than 1 minute more like 15 or 20. Just squeeze a hose to know if the system is pressurised.
The pressure is roughly linear with the coolant temperature guage on the dash, when it reaches operating temperature it's pressurized.
So if you're getting pressure after 20 or 30 seconds, then you have a head gasket problem.
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