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Hi guys, not a good first post to make but my father is having trouble with his car and we can’t find what it is. I’ve searched high and low on the internet and 95% of results come back with the older model cars so its no help.
The car is a 2011, honda civic 1.8si.

Early in the summer he had a coolant hose split, only a small one ontop of the engine. I found it, replaced, bled the system and all has been fine for a good 4-5 months.

Recently there was a damp smell in the car and he noticed the passenger footwell was soaking, upon further inspection its coolant. He’s now having trouble where the heaters won’t work properly. They are blowing cold air, completely fogging the windscreen up and then every now and then they blow a surge of hot air then go back cold. The cars temperature is also going to maximum.
I thought it was just air so I’ve tried numerous times to bleed the system but it doesnt seem to be making a difference.

Has anyone got any ideas as to what it could be? I read it could be the heater core but that could cost a small fortune to replace if it is. I want to prove everything else first.

The top big coolant hose is getting warm but the but the big bottom one is staying stone cold which I thought could be the thermostat not opening.

This couldn’t have come at a worst time to be honest so any pointers in the right direction would be greatly appreciated.

Kind regards,
Nathan.
 

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Discussion Starter #4
I really think its the heater core, the steam coming from the heaters, smell of coolant and the puddle of it on the passenger footwell is all making me think its that at fault.

Think that means getting the full dash out of the car which will not be fun. I imagine the dealers would charge and arm and leg in labour to do that too.
 

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Discussion Starter #5
Looks like its definitely the heater core. Managed to get enough trim off in the footwell to look up at it and can see the coolant running out from the heater matrix ? time to find a guide on how to get the dash out.
 

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Gawd that's a nasty surprise and I hope it's not the heater core, I don't recall hearing it being an issue before.

Heat on/off definitely sounds like an air leak in the cooling system, that needs to be fixed quickly.

Try tracking the hoses to see if there is split that feeds the heater console. Although the hoses are usually joined in the engine bay with fixed pipework inside the cabin.

Maybe try bypassing the heater matrix completely and join the feed/return pipes in the engine bay. Get the engine up to temperature and then test the rad hoses to see if the radiator is receiving and processing the hot fluid.

If the thermostat is working then both rad hoses should eventually get warm.

You may need to bleed air from the engine/hose high points, some heads/etc come with bleed nipples for this very purpose.

Let me check the Lings Honda website for an exploded diagram of the heater matrix...
 

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if your seeing coolant in the cab at what rate are you loosing coolant ?

there's a couple of things than can cause a leak such as badly fitted hoses , age related corrosion or perished rubber and pressure splitting the hose

if you can bypass the heater matrix like farqui suggested and after you have bled the system the temperature is still going into the red the thermostat would be the next thing to look at
a tell tail sign of a stuck thermostat is the radiator would be cold ( allowing for some thermal convection ) as the coolant wouldn't be flowing through it

unfortunately a failed head gasket can have some of the same symptoms as a stuck thermostat such as the radiator not getting evenly hot and if the top hose hose pressurised when the engine is running that pressure has to come from somewhere and pressure in the system could explain why you now have a leak and maybe the split hose you replaced especially if the hose looked in good order and not perished

first thing cure the leak and check the thermostat hopefully it will sort your problem out iv'e not really heard of head gaskets failing on these civics and it's a long shot but stranger things happen
 
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