If you are replacing the o-rings, you may as well replace the core too because the entire black assembly containing the HVAC system needs to be removed.

I replaced my heater core and o-rings 2 weeks after I bought my discovery.

Trying to replace the o-rings or heater core without removing the HVAC assembly is just wasting time and wishful thinking. At the same time I removed my seats and carpets and cleaned up the floorboards with POR-15. Having the seats removed helped a bit. Removing the steering wheel is not necessary but evacuating the A/C is.

I think it's worth doing yourself but I wouldn't want to do it often.

 

Okay well I removed a bracket in front of the heater hoses and I can see where they attach to the heater core. To my surprise it doesn't look wet around the mating surface. Everything looks dry around the heater core. However I haven't pressurized the system yet to see what happens.


Can someone explain to me what happens when the heater core fails(or O-rings)? I had coolant soaking into my front passenger floorboard. Does the coolant leak into the AC drain or something?

The mechanic I spoke with said that if the core failed that you would see steam coming out of the AC vents. I didn't notice this, but I did see it steaming out of the passenger front floorboard, he said that would indicate O-rings.

Some thoughts?

 

If you want a less messy test, and have compressed air or shop vac (outflow) available; which both heater core lines taken apart under hood, and coolant removed (shop vac or blow out), you can blow air into the core, and squirt soapy water around the fittings - any pressure leak will make soap bubbles.

 

Well after pressure testing the o-rings are in good shape and held up. However coolant was seeping through the foam surrounding the heater core. So I'm guessing I've got a crack in there somewhere.

I think I'm going to attempt it myself. Spring break is coming up for me pretty soon so I will have some time to do it.

 

Shouldn't be too bad, used to do car audio had several dashes out for custom stuff and fiberglassing.
I'm doing mine in a couple weeks figure it'll take a day with kids/lunch and just generally taking my time.

I say do it yourself I'd have got into mine yesterday but I'm lifting it tonight/tomorrow and doing wheels then a few misc. Items so didn't want multiple projects all at once.

 

First, you need to starting taking care of this before you have to replace your pad and carpet, that is more expensive then the heater core replacement.
Second, start calling around to get cost for a heater core replace and quit waiting for us to guess what is really wrong with it.
By the way, don't let the dealer do the replacement, it will be cheaper to buy another truck then let them do it.
Get back to us and let us know what you find out.

 

I already got a quote from one of the more respected independent mechanics around here. I posted it earlier in this thread. As mentioned earlier I diagnosed the leak and it's not the o-rings. I've got the core bypassed. I'm not paying $890 for this no matter what happens. The dealership is not an option, I was just curious as to what they screw people for. I did manage to dry out the carpet fairly well by using towels and heavy tools and weights to push out more coolant. But I will pull it to be sure.

Went to pull apart and I found two D1's that I can get heater cores off of. I've already got 1 out almost.

Anyone have some tips on replacing the core? This should be a good learning experience for me.

 

I wouldn't waste time pulling a used heater core. Replacing the heater core is something you only want to do once and since you are planning on doing the work yourself, use some of the money you save and get a new one. It comes with new o-rings and clamps too.

I would also get new heater hoses too. If yours are anything like mine, you will have to cut them off but you probably already know that since you bypassed it already.

 

The lure of the cheap core is strong. If you plan to follow that trail, consider testing core before installing (hook up some lines, pump it up). Also flush it out in both directions, maybe even with some chemical flush. The core has hot coolant flow all the time truck is running, so you want it to be good.

 

I found this. It may help speed things up for you. I am new at this, so I do not know if it will work for your Disco.

Heater Core Replacement (Range Rover 4.0/4.6/P48)

--Mike