Heater Core leaking?

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Heater Core leaking?

Postby jello » Mon 20.01.2014, 07:33

I smell coolant with the heater on. Typical sign of a leaking heater core. I don't see coolant in the car or in the heat ducts though. My coolant level doesn't seem to be lowering. I have plenty of heat. Anyone know how I can do as much checking as possible before trying to remove the dash/replace the heater core?

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Re: Heater Core leaking?

Postby epipete » Mon 20.01.2014, 13:30

The matrix consists of two copper pipes that are integral to the body of the matrix, when the heater box is installed these pipe protrude through the bulk head into the engine bay and on the engine side of the bulkhead are connected to two hoses which supply and returns the water dependant upon a vacuum valve that is operated by the temp control knob in the cabin.

I merely provide this ramble in order to show that any water leaking in side the cabin must be attributed to the matrix as there is no other place from which coolant can escape within the cabin.

When my matrix gave out it dumped all the coolant, very rapidly, in the cabin and in my case, because the valve in the engine bay was sound I was able to turn the heat down and retain some coolant in the engine but even then I came back on a truck!

Apart from dismantling the dash to pull the heater box any evidence of coolant leakage from the matrix will be limited to the area of the transmission tunnel directly below the heater and, if sufficient loss has occurred, in the footwells, try running your hand below the heater box, you could also slide a newspaper underneath to see if any drips etc occurs when you are back from a run.

Beware though, what may be small leak now could rapidly worsen, so stay alert.

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Re: Heater Core leaking?

Postby Dave Eds » Mon 20.01.2014, 13:38

Have you checked the reservoir cap?

Possibly releasing pressure and smell being drwn in through vents.
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Re: Heater Core leaking?

Postby epipete » Mon 20.01.2014, 14:15

Dave Eds wrote:Have you checked the reservoir cap?

Possibly releasing pressure and smell being drwn in through vents.


Good point, but how would you check the cap? I just purchased a new one from SJs because inspection of my old one showed it to be completely rusted out!
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Re: Heater Core leaking?

Postby jello » Mon 20.01.2014, 15:25

Thanks for the replies. I'll do some more checking. I do know my coolant is leaking in the engine bay a little - but it is not enough to cause real problems. My reservoir tank had the side pipe break off. I repaired it with a threaded pipe fitting and some JB water-weld - has worked well. That isn't leaking, and my cap is good. I have small leaks around the thermostat housing.

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Re: Heater Core leaking?

Postby epipete » Mon 20.01.2014, 15:38

I wonder, as Dave Eds points out above, if you have a leak in the engine bay, whether or not it's from the filler cap, this would migrate into the cabin irrespective of heater position, can you smell it when the heater is off?
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Re: Heater Core leaking?

Postby Simon_P » Tue 21.01.2014, 01:18

The air intake is next to the radiator bleed valve.
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Re: Heater Core leaking?

Postby jello » Tue 21.01.2014, 18:14

Yes, I can smell it when the heat is off. Not nearly as intense, but I can. It could well be my leak at the thermostat housing - which I have tried numerous times to stop. No success there. I'll try that again, band I'll also try looking in the tunnel for leaks, and putting some newspaper in there to watch for wetness.

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Re: Heater Core leaking?

Postby epipete » Tue 21.01.2014, 18:23

Not in the tunnel, (unless you have really serious fumes in the engine bay) there is now't there to leak! If it's leaking in the cabin it'll be right below the heater box. The box is suspended slightly off the tunnel so there is a fingers depth between it and the carpet, the only possible impediment here is a rod which runs diagonally from the heater control knob to the rear left of the heater box.

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Re: Heater Core leaking?

Postby 666 » Sun 16.02.2014, 19:47

Hey Phil,

Just had a problem with my thermostat housing gasket - would seal 3 times so eventually I just tried silicon gasket sealant with no paper (from halfords) and it work perfectly :)

I actually have a problem with my heater at moment - coolant leaking somewhere (doesn't seem to be in engine bay!)and cabin filling up with what seems like misty condensation from the heater coming up from the driver footwell and so can't demist the windscreen. Once all coolant gone then the heat reduces but de-mists - I think my heater matrix is leaking and dreading that fix pulling out the dash fascia!

Have you fixed yours yet?

all the best

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Re: Heater Core leaking?

Postby Brit-Car-Nut » Mon 17.02.2014, 00:02

Slightly off topic, but the Thermostat leakage issue is a common mention, so I thought I would put in my 2p's worth.

The thermostat sits in a recess in the housing that makes it very difficult to get it back in place and the cover back on without the thermostat dropping out of the recess and causing a leak.

The best way to install the thermostat is to completely clean the recess where it should stay and then use a little bit of quick drying gasket sealer to "hold" the thermostat in the recess. Then you can install the gasket, with a bit of gasket sealant, and the thermostat outer cover. This should resolve any leaking caused by the thermostat not staying in the recess when you are putting everything back together.

Another issue that should be watched is that most thermostats have a "jiggle pin" or a hole somewhere in the main flange. The pin or hole (whichever you have) should always be positioned so it is at the highest point of possible, usually right at the 12:00 o'clock position. The hole/jiggle pin is there to allow pressure (and a small amount of coolant) to bleed through the cooling system while the thermostat is closed. Putting it at the top makes sure the thermostat is always fully immersed (saturated) in coolant when the thermostat is closed.

Back on topic, everyone getting fumes inside the car but no evidence of coolant leaking needs to check all of the hoses to make sure none are weeping due to loose or damaged hose clamps. Fresh air for the heater comes from an inlet inside the engine bay and it is connected to the main duct in the front clamshell by a crappy foam sleeve that probably has disintegrated by now. Since the inlet is in the engine bay and probably not connected to the fresh air duct anymore, any fumes in the engine bay will be sucked up by the heater fan.

I have also seen the hoses feeding the heater matrix from the engine bay start to leak and some coolant will push past the nipples on the matrix and into the heater box which then gets heated by the matrix and fumes get passed into the cockpit by the fan system.

The cap on the overflow tank uses the same thread as a BMW 3 series, so you should be able get your local repair shop to pressure test the cooling system to look for leaks while the engine isn't really hot. Sometimes the hoses leak a little when the coolant is cold but under pressure but seal better when they warm up...
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