From the 6gc forum.
Nial wrote:
Another option might be to add a small oil cooler type radiator on the turbo water return line as that will be very hot.
The trouble with cooling the water too much is that it will just close the thermostat and restrict flow and could in extreme conditions lead to thermal shock which I guess might be unlikely, but do remember datajon mentioning something along those lines and as he builds race engines for a living I guess he knows what he is talking about.
yellowchinaman wrote:
Nial you're like magicman. I can always trust you with a constructive opinion and pick your brains smile.gif
Well the purpose of improve the cooling mainly helps speed up cooling time not actually lower running temp and even if it does, then it'll only be by a little. When driving, the engine will still heat up as normal when the thermostat is closed no matter how big or better the rad is up until the point it gets hot enough for the thermostat to open which then the cooling begins so I don't see how improve cooling will stop the thermostat from opening.
The thermostat is a linear proportional device which goes from slightly open to fully open over a span of a few degrees. It effectively mixes uncooled water from the bypass pipes with cooled water from the radiator and will adjust it's opening amount to give the correct temperature of 'mixed' water. The colder the water coming from the rad, the more closed the thermostat will be. This is slightly self-defeating in that reducing the flow through the rad will lead to the water cooling more and will then close the thermostat further, etc. etc.
The upshot is that an over-efficient radiator will reduce the flow through the engine substantially, and will reduce the pressure at the pump inlet potentially leading to cavitation at high RPM. (
http://en.wikipedia.org/wiki/Cavitation ) Also, if the temperature of the water from the radiator is much colder, there is the chance of rapid temperature variations of the water going in to the engine, as pressure surges due to RPM changes cause different mixing. Another good reason to drive gently until everything is properly warm.
Another common mistake is to think of the water entering the engine as 'cold' and the water leaving as 'hot'. Provided the flow rate is high enough the water coming out of the engine should only be slightly hotter than that going in, and likewise the water shouldn't be in the radiator long enough to cool massively. The water is effectively just conducting the heat from the engine to the radiator metal surface where the heat is transferred to the airstream. The faster the water flow, the less temperature differences throughout the sytem, and this is desirable. Temperature gradients, and especially rapid temperature changes, are what cracks blocks and heads.
As regards the turbo outlet, I haven't measured temperature but I would expect flow to be sufficient to prevent it getting too hot. Even if it were, it returns to the main flow through the radiator and has plenty of time mix. If the flow is small compared to the main flow, it's effect on overall temperature is negligable. Provided the main radiator copes with ALL the heat produced by the engine, there is no problem.
_________________
If at first you don't suck seed, try drier grain.