L400 heater core leak

macro · Post by **macro** » Fri Jul 03, 2015 4:58 am

Hey all, seems I have a slight heater core leak. When I turn the heat on in the morning the windows fog up for a minute and I can smell coolant.

Coolant level has barely dropped so it's nothing huge yet, just wondering if anyone has had any luck with the Bars liquid aluminum stop leak or something similar they can recommend?

I will replace the heater core eventually but I have wedding to pay for in a couple months first. Can anyone give me tips on core replacement or where to source one? Is it worth buying new or is used ok? I know the whole dash has to come apart...

Post by **Big-Bird** » Fri Jul 03, 2015 7:32 am

the most common leak point on the heater core is on the top tank.

The heater core in the L400 is held in the HVAC box with a foam gasket and a stamped steel bracket. This bracket isn't very big, roughly about the size of a $1 coin. As the foam gasket wears out over time it allows the heater core to wiggle slightly which allows the core to rub against the steel bracket and eventually a pin hole forms.

The heater core can usually be fixed with a small tiger torch or a heavy duty soldering iron and plumbers solder used for copper pipes. I have a few pics and can show you how its done.

Bring a lunch dude! The job to R&R the heater core is about 7-9 hrs and requires some new heater core hoses as the old ones must usually be cut off the heater core tubes.

A heater core can also be taken to a rad shop and they can fix it cheaper than a new core.

macro · Post by **macro** » Fri Jul 03, 2015 8:24 am

I'm a plumber so soldering is no problem, especially if accompanied by pictures! (Please and thank you!)

I'm only assuming from what I've read online that it's the heater core since I get a foggy windshield and a coolant smell. Would the location you mentioned cause that?

I know it's a huge job, is it drivable white the dash is being taken apart?

One last thing, is it worth it to use a stop leak for now until I can tackle this? Or can it cause more harm than good? Phew. Thanks!!

Post by **Big-Bird** » Fri Jul 03, 2015 5:42 pm

Using stop leak works for the short term but then the leak may not show up when it comes time to repair it.

No the deli can't be driven with the dash out or even loos. Truth be told the dash actually doesn't get fully removed, its get pivotted up towards your rear view mirror and that gives enough room to pull the hvac box. Lots of heater controls, radio, instrument cluster, glove box, dash air bag all come out. Lots of bolts and screws and sharp metal edges. Everyone who has done this job without gloves has given blood to the repair gods.

I'll pull the pics later tonight end send em. If you're worried about coolant in the cab then get a piece of plastic/copper pipe and pull the hose ends of the core and connect them with your pipe splice. This is all done around your intercooler. and it will prevent fogging, won't affect your hvac and it will stop the sickly/sweet smell from being in your cab.

If the leak is elsewhere on the core get a pro to fix it, unless you are able to control the heat around those cooling fins. I found my air nozzle with rubber tip was able to pressurize the core while it was held underwater. The leak showed up instantly. mine was a series of pin holes from that stupid bracket.

macro · Post by **macro** » Fri Jul 03, 2015 6:56 pm

Hmm, the bypass sounds like a good test too just to make 100% sure it's the core.

So, I have to open the dash, pull the core, get it fixed, sacrifice blood, re-install with new hoses, put dash back together. God dammit. At least it sounds cheap-ish and just super labour intensive.

Other option, pour some stop leak in every time it smells.....

macro · Post by **macro** » Sat Jul 04, 2015 11:08 am

Could somebody confirm that these are the heater core supply and return?

Post by **Big-Bird** » Sun Jul 05, 2015 1:16 am

Yeah, that's them.

you may be able to remove the hose ends without cutting the hoses but there is a risk of crushing the heater core inlet/outlet tubes. Its really tight, I slit the hose ends about 1inch from the end and then worked a radiator hose tool (a hook) around to loosen the hoses. Delicate work but it allowed me to reuse my heater hoses.

You have the rest spot on. Air tools make it easier but a power drill will work too.

macro · Post by **macro** » Sun Jul 05, 2015 8:13 am

Thanks, I responded (couple months too late) to your PM the other day too. My notifications get lost in this new layout.

macro · Post by **macro** » Fri Jul 10, 2015 6:16 pm

Alright, well I've bypassed the heater core for now, new hoses are on order. If anyone sees anything wrong with what I've done, please speak up!

Here's a close up of the inlet and outlet of the heater core. These are located behind the intercooler on the firewall. I tried to loosen the clamps and get the hoses off but there was no way in hell that was going to happen. Big-Bird Do these need to be cut off when I pull the core out or will they come off with it through the firewall?

I bent a piece of 5/8" soft copper in a 180º, once I cut the hose I realized it wasn't quite large enough so I soldered a couple couplings on the ends and that was perfect.

Tightened everything, put the intercooler back in, ran it up to operating temp and topped up the coolant. I have a 400km round trip tomorrow so cross your fingers for me!!

macro · Post by **macro** » Sat Jul 11, 2015 6:39 pm

Well, 400km later and it's perfect. Also for some reason my temp gauge is working again. It's been intermittent at best for a year or more. WEIRD. Maybe I knocked something when I pulled the intercooler.

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