don't pinch off the heater core hose

[scottmcphee]

I'm sick of the warm air blowing out the vents and having to use A/C even on cool days just to get cool air inside the car. This is a well-complained-about issue... not only of Legacy's but other cars lately. (The root cause for Legacy is a poor air exchange box design combined with continuous flow through heater core... seeps heat into any flow going through the climate control system).

 

On my other car, there is a "mono-valve" in-line with the heater core hose that shuts off coolant flow unless heat is called for by climate controls. This car blows cool through the vents when it's cool outside, like you'd want. So I thought I'd just try pinching off the heater core hose on the Legacy to see if that stops the warm blow issue... Don't do this.

 

I went for a 10 minute drive in the a.m. at about 80kph / 50 mph to test it out. The car shows nearly overheating on the gauge!! I pulled over and the electric fan is blowing, and this is ridiculous - the car has had absolutely no cooling issues or even gone past normal operating temp before. And this was a flat ground drive not even hot outside. I feel the engine, the radiator, the heater core hoses, and nothing is burning to the touch. So WTF!?

 

Not wanting to chance overheating, I take off the heater core hose pinch and all returns to normal. Plus I get warm air blowing in the cabin again... yeah.

 

Lesson: the car needs coolant flowing through the heater core for normal engine cooling operation. Stupid if you ask me. Go ahead, ask.

[devilmademedoit]

I eas going to try and bypass my heater core to troubleshoot my high engine temp problems. I guess maybe its not a good method to use.

[BAC5.2]

Subaru's have always done this, unfortunately.

 

You could always build a switching device, but that seems kind of excessive.

[scottmcphee]

Subaru has always done this? ... hmm. Weird. Is this so they can engineer the front radiator smaller and depend on the heater core to cool the engine? Putting the heater core in series with critical engine cooling system just seems ... stupid.

 

I am thinking bypassing the heater core would be OK, just don't block the flow on that coolant circuit.

 

This is what I'm facing too. To do it right, instead of a simple on/off valve I'd need to have to rig a selector valve that either routes coolant through the heater core, or around it on a shunted path. I know I could get a "duo-valve" to accomplish just this (from an old Mercedes), from a nearby wrecker is $8.

 

Or I could try a parallel bypass system with one branch always flowing, and put the one on/off valve on the heater core branch. So when it shuts off there is still flow on this circuit. The downside being that I only get "half" the volume of heat flowing through the core, at best. But I'm thinking that is more than enough even on our coldest days.

[BAC5.2]

The radiator is sufficient for cooling the engine, but tying directly in saves complexity. Other manufacturers do it too, so it's not some goofy Japanese thing.

 

It is absolutely fine to bypass the core. In fact, many people with older cars do because the heater core can develop a leak, and drip coolant into the car. You can simply cut the hoses going to the core, cap them, and use a straight connector to connect the two loose hoses.

 

I like the Duo-Valve option. Since you have a 2.5i, you have manual climate controls. I'd just put another switch on the dash to select bypass or not.

[GTTuner]

Funny,.... My car does not have this issue.

[ehsnils]

It's the same with many Japanese cars. Full flow heater core.

 

But mounting bypass valves should be simple.

[frank_ster]

It has to do with the fact that the thermostat is on the bottom of the engine

You can byPass the heater core but don't block the hose it circulates the coolant through the engine and turbo.

[burnout8488]

Interesting, I have not noticed this problem at all on my auto-climate equipped Legacy.... or have heard of it ever. Is this only a manual climate control issue?

 

I set my climate to 65º, turn it off, and set the air intake to "fresh"... always gives me a nice outside-air-temp breeze coming through the vents.

[frank_ster]

mine is a limited, and it gets very hot air blowing through the vents after a while. but the ac system has been removed for the time being. i was thinking it was the evaporator core getting hot from the under hood temps.

 

i don't think its the mixing system that is made poorly, other wise the ac wouldn't work well.

since everything goes through the evaporator first then the mixing. but since its still hot out i'll disconnect my heater core and see if it makes a difference.

[BAC5.2]

I set my climate to 65º, turn it off, and set the air intake to "fresh"... always gives me a nice outside-air-temp breeze coming through the vents.

 

That's how the Auto control operates, and I've noticed the same thing. You get roughly ambient air through the vents when you do that.

[liljonson]

yea... never block of coolant lines... lol lesson learned

sometimes the best way to learn is by making mistakes!

[ouch1011]

Coolant bypassing the thermostat to the heater is what allows the coolant around the thermostat to warm up and open the tstat.

 

Most of the heater control valves I've seen have 3 ports--1 input, 1 output to the heater core, and 1 output/bypass back to the engine.

[scottmcphee]

Coolant bypassing the thermostat to the heater is what allows the coolant around the thermostat to warm up and open the tstat.

 

Most of the heater control valves I've seen have 3 ports--1 input, 1 output to the heater core, and 1 output/bypass back to the engine.

 

This was exactly my suspicion - some flow in the heater core branch is required to warm the T-stat.

 

I think I'll do a parallel bypassing with a single manual valve on the heater core branch, initially. This avoids the complexity of electrical switching of a coolant mono-valve, or duo-valve.

 

Considering this is mostly a seasonal issue - in the hottest of months that are very few where I live. Just open the valve for fall/winter/spring when defrosting heat is sometimes or always required, and close the valve for summer.

 

If this becomes a pain in the neck in the fringe seasons fall/spring, then I'll automate and tie in the electrically controlled valve to the climate system, or a switch of its own.

 

Thanks for the discussion!