[DeTomaso] More on Cooling

[John Taphorn]

Hey guys, I heard from one of our precious informational resources today who was monitoring the list, but unable to post.  His name is John Christian (JC), a Pantera owner who worked as an engineer for Roush Racing over many decades.  JC is a humble gentleman who knowledge of anything automotive certainly eclipses mine by at least a power of ten.  When JC speaks, I listen. He called me at work this afternoon to chime in on the ongoing cooling thread that has been discussed recently.

 

He wanted everyone to appreciate the importance of retaining the by-pass feature in the Cleveland engine.  Without the bypass during warm up, coolant pressure is high in the block as the pump spins pressurizing the vessel.  At start up heat energy, via conductivity, eventually migrates through the coolant to the thermostat and it begins to open.  Not all the way at first.  Although in short order, very hot coolant surrounding the combustion chambers reaches the thermostat and the thermostat recognizes the need to open fully.  When fully open the thermostat probably allows about 25 gallons per minute to flow.  In a matter of seconds, the block is emptied of hot coolant and displaced with cold coolant.  This thermally shocks the engine causing dissimilar metals to contract at varying rates.  Our cast iron blocks are very durable and can tolerate this abuse for a while; however, it is less than an ideal scenario that eventually may create complications.  The diffent expansion/contraction rates are is tough on gaskets; especially when they are sandwiched between aluminum and iron.  This may accelerate leaks at the aluminum water pump and aluminum heads.

 

In contrast, utilizing the bypass allows coolant to circulate through the system prior to the thermostat opening allowing the coolant on the low pressure side of the water pump to rise in temperature and reduce the temperature differential and resultant thermal shock to the engine when the thermostat opens.  This would make a case against using a Weiand type water pump that eliminates the by-pass feature when not redesigning the system to accommodate a separate bypass or bypass thermostat housing.

 

As an aside, JC estimated that while flow exiting the block through an open thermostat may be about 25 gals/min, without a thermostat it may be 60 - 90 GPM.  For those of us that have incorporated a remote by-pass thermostat and eliminated the conventional thermostat in our cooling systems, that in an impressive leap in flow circulation during start-up. 

 

JT