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NEED: A concise Coolant Flow diagram

mitsuturbo

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Jun 2, 2008
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Near Seattle, Washington
I'm nearing completion of my engine build, and this is to include water lines for the turbo and wastegate. I need a very concise coolant flow diagram, which includes the throttle body, factory pancake oil cooler, heater core, thermostat, and radiator.

I honestly don't even know which way the coolant flows through the engine and water pump.

If anyone could help here, i'd greatly appreciate it, and it would be a valuable asset to the Technical Article collection.

Thanks.
 

Barnes

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Feb 9, 2003
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Richland, WA
I don't know if such a diagram exists, but I can explain quite a bit;

In our cars, the waterpump draws in water from the big front water pipe, and then pumps it straight into the block. Therefore the water pipe is the lower pressure point, and the entrance of the water into the block is the high pressure point. This means that coolant will always flow from the hot side to the cold side. I'll break down the flow for each component:

1)Radiator; Coolant flows out of the water pump into the block, then around the cylinders in the block. Then coolant flows through holes in the block deck, and into the cylinder head, then finally flowing out through the thermostat housing mount hole. Coolant flow is regulated by the thermostat, and when it is open, coolant flows out of the thermostat into the upper radiator hose and into the radiator. At this point the coolant is hot. Then the coolant flows down the radiator, is cooled, and flows out of the lower radiator hose. The coolant is at it's coolest point here. The water then flows through the front water pipe and back into the water pump and the process is repeated

2)Heater core: Coolant flows from the port on the thermostat housing, to the heater core, then out, and back into the port on the front water pipe.

3)Throttle body: Coolant flows from the port on the thermostat housing, to the throttle body, then back to the port on the front water pipe. (The nipple tee'd off the pipe for the heater core line)

4)Turbo charger: coolant flow from the thermostat housing port, into the turbo center cartridge, then out through the curved metal line under the turbo and into the front water pipe. What is odd about this situation, is that hot coolant from the thermostat housing is being used to cool the turbo. NOT cool coolant. It is impossible* to do it any other way really.

5)Oil cooler (stock oil/water style): Water flows from the thermostat housing, down the hardline bolted to the front of the block. From there it goes into one port of the oil cooler, then back out and into the nipple in the front water pipe just before it enters the water pump. Again, same situation as the turbo charger. You have hot coolant being used to cool something. Probably another reason the stock oil/water style oil cooler doesn't work that well.

As you can see, you always have a flow that goes from hot to cold. This is due to the way the system is designed. So if you need to run coolant lines to a turbo, use a port or tap the thermostat housing, run it to the turbo, then run the coolant outlet to the front water pipe. You can still use the existing flared fitting port that the stock hard line uses with a custom line with the right fittings.

*It is not really impossible, but if you wanted coolant to flow from cold to hot, you would have to install an independent electric pump to draw from the cooler front pipe, pump it through whatever device, and then exit out to the thermostat housing. You could do it, but a terribly impractical thing if you as me.
 
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mitsuturbo

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How strange. I always thought the pump pushed hot water out of the block and into the lower radiator hose.


If this is indeed the flow direction, it will make it easier to set up my wastegate and turbo lines, now that i know.
Since i got an air-oil cooler, i was thinking i'd use the factory oil cooler ports for the MV-R wastegate.
 

turbowop

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Apr 29, 2001
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Yakima, WA
The upper radiator hose gets mad hot because all that coolant is coming from the motor.

And "hot" is a relative term. It may seem weird to cool the turbo with already "hot" coolant, but compared to the temps that thing sees, that hot coolant is probably much cooler. As far as the pancake oil cooler goes, it works to keep the oil temps near the coolant temps, which helps get the oil up to temp in the winter, it's not just for cooling.
 

mitsuturbo

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I found this for a mazda pickup. I'd guess ours is pretty much the same, as how Barnes described it. Right?

G6CoolantFlow.jpg
 
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belize1334

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Nov 18, 2003
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Bozeman, MT
What's always confused me is the functionality of the overfill tank. I know that when coolant exceeds a certain temp the vapor pressure rises above 0.9bar and the cap deflects allowing coolant to outgas into the overfill tank. What confuses me is how this coolant can then be drawn back into the radiator after it's cooled. Presumably there is a vacuum drawn in the system now that the coolant is at a lower temp but the cap would seem to be a one-way check-valve so I don't see how the coolant can get around the cap and back into the radiator once the pressure drops.

Edit: Answered my own question. The cap has two valves, one for each direction, to allow vacuum to draw coolant back into the system.
 
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Barnes

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Also be aware that the coolant probably does not exit the cap as vapor, but as a liquid. As you heat up the coolant in your cooling system, the liquid expands due to thermal expansion. So if your radiator is 100% topped off, that expansion has to go somewhere. So it gets pushed out the radiator cap as liquid once the pressure hits 0.9 barg as you stated. This is why all cars have overflow tanks, or expansion tanks. I hate the expansion tanks personally, but they are technically better for certain reasons.

I would guess the only time it leaves the radiator as vapor is when the coolant is actually boiling, or if your coolant system isn't full and the coolant gets hot enough to generate enough vapor pressure to open the radiator cap.
 

Barnes

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Feb 9, 2003
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Quoting mitsuturbo:
I found this for a mazda pickup. I'd guess ours is pretty much the same, as how Barnes described it. Right?



Since no one replied, yes, this is how I described it.
 
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