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How to bypass the heater core to stop the engine overheating


Guest boostin
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Guest boostin

A blocked heater core is worse than you think. 90% of the coolant flow when the engine is cold is through the heater core. It is this flow that opens and keeps open the thermostat. If the flow is insufficient, and it doesn't take much to restrict it slightly, the thermostat won't open and you get overheating issues.

Bypassing the core completely is one option, but that causes another set of problems in winter with defrosting windscreens.

What I do is get two 5/8" plastic tee's from Repco and splice them into the heater hoses and run a link between them. Its a fairly cheap repair as its around $20 in parts. This ensures good coolant flow to the thermostat, but still allows some flow through the core for heating and demisting. You need 2 of the tee's (Repco part # is 28634EA), and 6 hose clamps to suit 5/8" heater hose.

Here's a shot of the twin turbo I fitted this to today.

DSC00134.jpg

I find a suitable section of heater hose, chop out about 20mm of hose, fit the tee, and then do the same for the other hose. Then with a new piece of hose, join the 2 tee's together. Quite simple and effective, and takes about 30 mins at most.

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Guest boostin

Usually it does as the air in the lines tends to go through the bridge. There was a bit of gurgling in the WRX before I did it, and none after, but the twin turbo (pictured) never had a gurgle. Just started getting a bit warm after a motorway run.

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Guest SPANKU

there are reason why engine overheats. doing this mod wont do shit all im sure of it. once these EJ20 start over heating try to find the cause of it.

maybe doing this mod will make the water flow abit better and wont cause your heater core to burst?

i know the fact that once your motor start giving a sign of cooking, my advice is to look for the cause ASAP

this is a good idea though. thanks for sharing

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 SPANKU said:

there are reason why engine overheats. doing this mod wont do **** all im sure of it. once these EJ20 start over heating try to find the cause of it.

maybe doing this mod will make the water flow abit better and wont cause your heater core to burst?

i know the fact that once your motor start giving a sign of cooking, my advice is to look for the cause ASAP

this is a good idea though. thanks for sharing

Here he is talking about the blocked heater core being the cause. This is his solution for that cause.

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Guest SPANKU

i had this same problem with my first wrx and my ra. it was really annoying driving on the motor and it just burst and steam everywhere in the car and front windscrean

its a good idea like i said. but i wont say it will stop a engine from over heating though?

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Guest boostin

It won't stop the core bursting as a fluid exerts the same pressure at all points in a container. All this does is save you the hassle of pulling the dash out and fitting a new heater core, if you have no problem with the heater not giving a lot of heat that is.

If you want to test the theory, loop one of the heater hoses back to the engine. Just try not to get any kinks in the hose.

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Guest SPANKU

yeah this is a common problem with some older wrx and legacy. it is a pain in a asss to remove the dash and also getting the right ones too what i know is that version 4 and 5 are not the same ones

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  • 3 weeks later...
Guest boostin

And just so you know, I ended up pulling the dash out and replacing the heater core anyway!! It was so blocked and the bypass so effective that it had almost no heat from the blower fan!! Not a good look on a car you're trying to sell!! :-X

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hi, has anyone done this on a wrx im trying to do it on a 96 wrx sti v2 and looks like the amount of gap the t join creates between the two hoses is too big and puts hose in the way of the clutch fork movement. any other ideas to solve my problems

the two heater hoses goes to the passenger side of motor so one cuts accross where the clutch fork is.

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Guest the_return_of_the_jedi
 turborunner said:

hi, has anyone done this on a wrx im trying to do it on a 96 wrx sti v2 and looks like the amount of gap the t join creates between the two hoses is too big and puts hose in the way of the clutch fork movement. any other ideas to solve my problems

the two heater hoses goes to the passenger side of motor so one cuts accross where the clutch fork is.

get a longer hose 8)

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Guest the_return_of_the_jedi
 subaru-mania said:

My bf5 gt also Makes the bubble/gurgle noise In some gears when yu put your foot down, However It never gets hot on the temp.... Will it? or should I worrie about it?

its the trolls..

its charachter....

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Guest boostcut

spray the hose so its lubed up. you dont just ram it in aye :P and then bend the wire about 20mm from the end and use it to work the hose onto the turbo. its quite easy to do. a twin turbo is where the fun is at.

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