Frank818
07-07-2015, 06:28 PM
I have a question not Subaru related, but any engine and any water-cooled turbo related.
I know some turbos are meant to use water cooling from the engine's cooling system (like Garrett's) and that they (at least the Garrett's) have been tested by the manufacturer at a 50/50 mix @ 91C (196F). 196F is normal engine temperature and sometimes is in the area where the coolant flows through the rad (thermostat opened), but sometimes the thermostat opens higher (200F+).
The way most engine's cooling flow works is that the thermostat stays closed when cold, so the coolant circulates around the engine block, heating up as fast as possible to reach normal temps as fast as possible (cold engine is not good). Then when it gets hotter, the thermo opens and allows flow to go through the rad, cooling down the coolant that goes back to the engine block.
I have to 100% build my own lines and routes, due to the many changes I have applied on the engine and 818. I am not re-using anything from OEM.
Based on that, I have 2 choices to route my coolant lines to the turbo housing:
1- I use hot lines, for example right off the head and back into the system that circulates around the block when the engine is cold. The good is that it allows to keep the turbo cool by constantly (not thermostat dependent) flowing coolant through and heats up a little faster (theoretically) the engine cuz the heat from the turbo adds up in the lines. The down is that at normal temps the coolant is around 190-210F, which may cool less the turbo. Don't know if that is really a problem or not.
2- I use cold lines, for example right off the tube at the bottom of the rad (well the hose in the engine bay connected to that tube). The good is that the coolant is colder which cools down the turbo. The bad is that there is no coolant circulation through the turbo until the thermostat opens, so if I run at 194F and the thermo only opens at 195, nothing will cool the turbo. Sure I can get a 160F thermo, but let's stick to the principle behind my question, here.
Apparently, that water-cooling system is mostly to prevent heat soak situations when the engine is shut down.
So, if it's true the purpose is mostly when the engine is shut down, then do any of the above 2 choices really matter?
That's the question and I am not an expert enough on turbos to know the answer. Maybe there's a pro somewhere who has an opinion.
I know some turbos are meant to use water cooling from the engine's cooling system (like Garrett's) and that they (at least the Garrett's) have been tested by the manufacturer at a 50/50 mix @ 91C (196F). 196F is normal engine temperature and sometimes is in the area where the coolant flows through the rad (thermostat opened), but sometimes the thermostat opens higher (200F+).
The way most engine's cooling flow works is that the thermostat stays closed when cold, so the coolant circulates around the engine block, heating up as fast as possible to reach normal temps as fast as possible (cold engine is not good). Then when it gets hotter, the thermo opens and allows flow to go through the rad, cooling down the coolant that goes back to the engine block.
I have to 100% build my own lines and routes, due to the many changes I have applied on the engine and 818. I am not re-using anything from OEM.
Based on that, I have 2 choices to route my coolant lines to the turbo housing:
1- I use hot lines, for example right off the head and back into the system that circulates around the block when the engine is cold. The good is that it allows to keep the turbo cool by constantly (not thermostat dependent) flowing coolant through and heats up a little faster (theoretically) the engine cuz the heat from the turbo adds up in the lines. The down is that at normal temps the coolant is around 190-210F, which may cool less the turbo. Don't know if that is really a problem or not.
2- I use cold lines, for example right off the tube at the bottom of the rad (well the hose in the engine bay connected to that tube). The good is that the coolant is colder which cools down the turbo. The bad is that there is no coolant circulation through the turbo until the thermostat opens, so if I run at 194F and the thermo only opens at 195, nothing will cool the turbo. Sure I can get a 160F thermo, but let's stick to the principle behind my question, here.
Apparently, that water-cooling system is mostly to prevent heat soak situations when the engine is shut down.
So, if it's true the purpose is mostly when the engine is shut down, then do any of the above 2 choices really matter?
That's the question and I am not an expert enough on turbos to know the answer. Maybe there's a pro somewhere who has an opinion.