Heater bypass hose

[TouchStone]

Wouldn't it be better to delete this hose to prevent coolant from skipping by the radiator? I know the 818 manual says to connect them with a hose I just want to know why.

40887

[Buzz Skyline]

I wondered that too, but followed the manual just in case. Here's an older Impreza coolant flow diagram that makes me think capping it off would be better.

http://porcupine73.com/pics/coolant/coolant-flow-diagram.gif

[wallace18]

The thermostat will not work properly if you cap them off.

[xxguitarist]

Yep, what Wallace said.
The cooling system is a little unique on the Subies.
You definitely do need to have recirculating flow to the water pump/thermostat from the crossover, otherwise you won't have correct temp sensing.

[Buzz Skyline]

If the diagram is similar to the WRX (can't say for sure, because I haven't found a WRX or STI diagram yet), then the flow will still go to the water pump and everything else as before. The heater core circuit is in parallel to the throttle body/idle air circuit. Removing the parallel circuit will increase the flow resistance a little, I believe, which might make the pump work slightly harder. It will also push more coolant through the throttle body/idle air circuit, but the rest of the cooling system shouldn't act any differently.

To be certain, of course, I'd have to look at the actual WRX/STI diagram.

[xxguitarist]

Ah, so I was assuming most of us had deleted the throttle body heater ;)

[Buzz Skyline]

I think I stand corrected. If this is an accurate diagram of the cooling system in an WRX, then it looks like Wallace18 and Xxguitarist are right, the flow from the heater circuit seems to be the main way the thermostat is heated.

http://www.dunebuggyarchives.com/static/attach/78/6878/Picture5.png

Deleting the circuit would potentially prevent the thermostat from opening at the right engine temp.

[TouchStone]

So here is what I found from the 2003 manual. I see an extra bypass flow running in parallel with the heater and the throttle body but its unclear about where this is and I can only guess its from the water tank? This should serve the purpose of opening the thermostat at the right temperature, or is the water flow not great enough?

4088940890

As a theoretical question, can the thermostat be removed entirely? Would this negatively impact the engine or cooling system?

[Quiny]

I put a tee in were the heater bypass hose goes then plumbed the extra line back to the water tank were the extra fitting is. (the fitting that used to go to the top right of the radiator). It behaves just like drilling and taping a hole for a fitting in the crossover pipe. I have had mine running for hours with no issues, gets up to temp then stays right there. Had no issues filling the system, didn't even need to burp it.

[TouchStone]

I put a tee in were the heater bypass hose goes then plumbed the extra line back to the water tank were the extra fitting is. (the fitting that used to go to the top right of the radiator). It behaves just like drilling and taping a hole for a fitting in the crossover pipe. I have had mine running for hours with no issues, gets up to temp then stays right there. Had no issues filling the system, didn't even need to burp it.

So, your heater pipe hose connects only to the water tank? or does it still connect to the heater return line?

[Buzz Skyline]

As a theoretical question, can the thermostat be removed entirely? Would this negatively impact the engine or cooling system?

The thermostat is pretty important. It's best for the engine to warm up as quickly as possible to get the oil flowing and protect the bearings. I've been told that it's particularly important for turbo motors. (I think it has something to do with forged pistons needing to heat up and expand.) Without a thermostat, coolant would flow through the radiator even at start up and it would take much longer to warm up to an appropriate operating temperature.

[Doutie]

The Impreza diagram that buzz posted is like a typical Ford 5.0 with one important exception. In the Suby system the thermostat controls the cold water coming from the radiator. Therefore when the thermostat is closed ( cold engine) the suction side of the water pump has no water to pump, whence the heater and throttle body circuits provide water to prevent pump cavitation and to circulate water back thru the block. This helps heat the motor to operating temp faster. In the case of a Ford 5.0 or other v-8s the thermostat controls the hot water going to the radiator. When the thermostat is closed the hot water is circulated thru the heater and back to the suction side of the pump, making the block loop for faster heating.

[Harley818]

I don't know where I read it, but I recall Mechie and others saying that the heater line needs to stay as a re-circ as it plays an important part in making sure you get good flow through both heads.

See post #24 and following - there is a whole discussion starting around post 9 or 10

http://thefactoryfiveforum.com/showthread.php?14184-looping-coolant-lines-together

Wayne says if you don't loop them your thermostat will never open.

[DMC7492]

Hi guys, how about plumbing the heater lines to another small type Setrab oil cooler for extra engine cooling. More weight and coolant but more heat capacity also.

[Bob_n_Cincy]

Hi guys, how about plumbing the heater lines to another small type Setrab oil cooler for extra engine cooling. More weight and coolant but more heat capacity also.
Don,
Adding the heater core is a good idea for another reason. It adds restriction in that line (like OEM). So when the thermostat opens it will force more coolant to the radiator. I am actually considering putting a flow restrictor in the coolant bypass hose.
Bob

[Quiny]

So, your heater pipe hose connects only to the water tank? or does it still connect to the heater return line?

It connects to the return line just like the manual instructs but I installed a tee in the hose that connects the 2 and run the third line back to the water tank.

[TouchStone]

How long does it normally take a cold engine (idling) to heat up and open the thermostat?

[Bob_n_Cincy]

How long does it normally take a cold engine (idling) to heat up and open the thermostat?
Hi touchstone.
See your answer in this post.
Bob
http://thefactoryfiveforum.com/showthread.php?12534-MRG-MotorSports-818S-Build&p=170417&viewfull=1#post170417