Replacing Faulty Heater Core in Volvo 850 Car




Introduction: Replacing Faulty Heater Core in Volvo 850 Car

A heater core is a small radiator (matrix) that transfers heat from the engine-cooling system to your car's air heating/ventilation system. The heater core is much smaller than the engine-cooling radiator in front of the engine. This instructable will show you how to replace a faulty heater core in a Volvo 850.

First diagnose the problem: is the heater core the prime suspect?

Some symptoms of a heater core leak are:
* you are losing coolant when the heater is used.
* you are NOT losing coolant when the heater is NOT used.
* you can smell antifreeze when the heating is on.
* you can see condensed vapour exiting vents when the heating is on.
* your car's footwell carpet is wet.
* windows steam up with soapy-looking film.

Heater core failure can be a major problem because of access difficulties. If your car is a Volvo 850 then the job is not too hard, but I wouldn't recommend trying this instructable unless your car has almost all of the above symptoms (heater core might not be the cause), are a reasonably competent DIY mechanic, and enjoy the challenge of working in inaccessible and unpleasant places to save yourself a large garage bill.

The job might take you approx 4 hours of solid work, largely depending on how much antifreeze leaks out and how much you care about cleaning it off the carpet), and it will be messy.

This Instructable illustrates the repair in a right-hand-drive Volvo 850 1994 GLT 2.5 AUTO. If your Volvo 850 is left hand drive then procedure is similar but you'll be removing the heater core radiator from right hand side instead of left. In either case: you'll be removing heater core from passenger side footwell, which gives you better access than driver side footwell.

All loose removable carpets should be taken out at first sign of coolant leaking onto them, and replaced by absorbent rags or newspaper.

You'll need:
* torx screwdrivers (several sizes) and philips screwdriver.
* rags
* dry newspapers
* plastic sheeting/bags
* carpet cleaning kit e.g. wet vacuum cleaner.

If the heater core does need replacing you will also need a new heater core:
* Volvo 9144221 Heater Core/matrix/radiator. An OEM (non-Volvo) part costs circa US$150 or £100).
* two o-rings (3545586S) for installing matrix - you can probably re-use the ones that are already there, but maybe be a good idea to replace whilst you have access.

I replaced my heater core after seeing info at - you might want to view that page too.

There's more info about Volvo 850 A/c & heating system at, but I wouldn't use hose clamps on the water pipes to core, because in my car they appear to be solid! So try to stop the pipes at outlet rather than by clamping.

Good luck!

Step 1: Passenger-side Footwell Access to Heater Core Case.

* Engine should be off and not hot.
* Disconnect battery.
* remove panel under passenger dash. Keep those screws in centre console tray.
* Peel down carpet carefully.
* Unscrew and gently remove black plastic panel to get access to white heater ducting.

Step 2: Driver-side Footwell Access to Heater Core Case.

You also need to gain access to the heater duct casing on the other side. The heater core is within this white plastic ducting/casing.

Now that you can see the white plastic heater ducting and two water pipes you should think before disconnecting the pipes: might the leak NOT be caused by the core being faulty? For example, is the leak coming from the connection between the two pipes and the core? Test for this visually and with dry tissue paper. If the connection is the problem, try tightening the central screw (mentioned in next step).
But assuming that the connection itself isn't the problem, this instructable will proceed with REMOVING THE HEATER CORE.

Step 3: Disconnect Heater Casing and Core.

* Unscrew two screws on each side of ducting.
* Ease the white casing apart at the black seal joint. Don't force it too far.
* After the seal is opened you need to detach water pipes (secured by 1 screw) to completely remove the lower part of the white casing, which has heater core attached to it.

Be ready for the coolant (fairly low pressure because engine is off). You might be able to create a waterproof reservoir under casing, using plastic sheeting and rags.

I found that the right hand pipe gushed a cupful of coolant then stopped. I quickly temporarily lashed the left hand pipe with bicycle inner tube, which completely stopped leakage even when left overnight.

Now you can carefully ease the heater core back towards gear lever, twist and shuffle it out via passenger footwell.

When you have removed the heater core and ducting, separate them by undoing four torx screws. It is impossible to replace new heater core the wrong way around because of arrangement of screws, so don't worry about noting the orientation.

You are now holding your heater core - let's hope it's faulty!

Step 4: Confirmation of Diagnosis

Confirm that core has a leak. This old core leaked (very slowly) just under atmospheric pressure after I filled it with water. Or you can flush with clean water, clean the pipe holes, fill with water, put your thumb over one hole and blow hard into the other hole hoping to confirm a leak.

Assuming you have found a faulty core, get yourself a new one:
Volvo 9144221 Heater Core/matrix/radiator (an OEM part costs circa US$150 or £100). Order new o-rings while you are at it.

Ft the new core into the white plastic using those four torx screws, and the o-rings on the pipe stubs.

I didn't check my o-rings and all was OK, but if for some reason they went missing or were damaged you would find that your system could leak at this joint. Don't take this risk.

Step 5: Reconnect the Heater Core.

Easier said than done! The new core is delicate, though a bit of scuffing to the very thin radiator fins/baffles shouldn't be a problem. Put the core back up where it came from, reconnect the two pipes (SPILLAGE ALERT!) and quickly secure that screw between the two pipes - I found that it went in easily first time even with very limited access in very sub-optimal conditions.
Once plumbed in screw the white ducting case back together - if you haven't already. Now the job should be functionally complete, so before replacing panels and carpets and TEST YOUR WORK:

Reconnect the battery
Top up your coolant under bonnet/hood, to mid-position (I found that this needed just 1 litre of coolant).
Replace cap securely on coolant reservoir.
Turn heating OFF. The heater core only gets pressurised when the heating controls are on AND the engine has warmed up after maybe 5 minutes.
Run the engine with bonnet/hood open (DANGER!) and if coolant level drops significantly switch off engine and check for leaks where you connected new core to two pipes. I found that coolant level DID drop but that there were no leaks from the system - I just topped up and assume that the coolant level drop was just due to flushing bubbles from the cooling system.
Run engine with heating ON (and wait for engine to warm up so hot air flows into car) to check that everything seems OK.

Hopefully you'll get the same result as I got: after one or two minor coolant tops up everything settled down nicely, there were no leaks from the core, no more noxious coolant vapors and condensates, no more wet carpets. If you can run the engine with the heater blowing hot air into your car and without any leak from the pipe-core joint, you're probably in luck!

Step 6: Assuming You've Fixed the Leak ...

If you had a lot of coolant leaking on the carpet before or during this repair will need to clean and drying your carpets.  I used carpet-shampooing vacuum cleaner and a bucket of slightly soapy water, repeated 3 or 4 times. Then a process of carpet drying which in cold weather could take days, but needn't stop you using your can in the meanwhile. Use absorbent rags or newspaper to wick the moisture from carpet. Leave for 12 hours then replace with dry newpaper/rags.

I also used silica gel bags because the weather was cold and damp. It's best to do this with the carpets exposed to help ventilation of the carpet. Also you will still have access to the heater core housing to double-check that that pipe joint isn't dripping even after the heater has been used.
When carpet is dry replace black plastic side panels, and carpets. Then fit the under-dash panels into position, taking care to connect the panels correctly with the guides before screwing securely. If the panel is not in its guide you'll be able to bend the edges unreasonably.

If you try this instructable, you are very welcome to 'Add Comment' about how you got on and how to improve these instructions. Thanks. Dom.

Spurious bonus material: This stunt was a part of a Swedish Volvo commercial demonstrating the 850's crash survivability.


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    10 years ago on Step 6

    Great write up, photos and annotations!
    It certainly helped give me confidence to tackle the job. Was able to do it in an hour, knowing exactly what to look for at each step thanks to this. So, many thanks!


    8 years ago on Introduction

    thanks for the feed back.

    actually i did this bypass operation, and run with the 2 hoses bridged for more than a year. no heating at all of course but i where confident about keeping the coolant at its workplace.
    i got a new core one month ago and now is working perfect again.
    Volvo 850 SW TDI with 390.000 km
    For me, the best car ever (for under 1500€)



    Reply 6 years ago on Introduction

    I have a Volvo 850 "love it". I also did this bypass, a year ago, did fine , no heat though, i had it rough during winter, could not get windscreen to clear. However now after a year, a problem has develped. The car overheats especially on prolonged idling, lke in traffic jams. Temp. shoots up, and hot steam, and coolant starts spewing from the reservoir plstic or expansion tank. The cooling fan at the radiator never comes on, even when the car overheats, I changed the thermostat no change. give an answer if you can at,



    9 years ago on Introduction

    great instructable!

    specially because you point out the screw that i was missing, the one inbetween the 2 pipes!!!! thanks so much

    just one question:
    lets imagine that i have no core replacement for a while and mine is broken with a big hole in the bottom (it exploded while cruising at the higway, with a huge steam flood, scary) but i am in the road and need to continue...
    can i just bypass the core with a piece of hose connecting the 2 pipes?
    i will loose heating but i will keep the coolant in his place (da engine), right?
    will it interfere with any other thing?

    good job


    Reply 8 years ago on Introduction

    You could just put your temperature controls all the way to cold, that would prevent coolant from traveling through the heater core.

    Your idea of connecting the 2 pipes would work, but I really doubt you would be able to feel much, if any, heat at all.


    Reply 9 years ago on Introduction

    Sorry that my expertise/memory doesn't stretch to giving you a reliable answer on this ... can anyone else here help lobo0x7?


    Joe McPlumber

    Thanks for this man. I didn't even imagine that anyone had done this, i only just Googled in curiosity since i got so far and didn't know what to do next. Too bad, too, because i've got the entire dashboard superstructure out in the driveway.


    Oh well it needed work anyway cause it rattles a lot, and the stereo was hooked up wrong. And i learned a lot about how all that mysterious stuff works back there.

    Anyway many thanks, and i'll pay it forward next time i fix something i know how to fix i'll be sure to document and Instructable it.


    9 years ago on Introduction

    One more tip, clean the heater core of the packing oil. It took a few days with the windows down to burn off all the oil. Thanks for the instructions it was very easy I did it on my lunch break at work.


    9 years ago on Introduction

    I recieved a "Heater Pip line" part from the volvo dealership they told me this was one of the pieces that needed to be replaced on my 97 850 turbo 2.4 along with the "heater hose" itself. Are these the right parts?


    Reply 9 years ago on Introduction

    Sorry, I can't help you with that ... I'm not a pro, I no longer have the Volvo 850 ... you might be able to tell from my pics whether that's a component of the system (it looks familiar). GOOD LUCK!


    9 years ago on Introduction

    Yesterday I was treated to a warm foot bath on the way to work. I thought this was the death of my 95 850 with 260,000 miles on it. Thanks to your instructable it will live to die sometime in the middle of winter, in a blizzard or nor'easter.


    Reply 9 years ago on Introduction

    Only 260,000 miles? I don't think this will be her last winter!


    9 years ago on Step 6

    Very Help full,I replaced my heater core in my 1999 V70 with one I bought on line at a auction site for $40,it was brand new and came with Orings and Foam Tape. your instructions were great! .trash bag was KEY to keep from flooding my cars carpet.
    Thank You VOLVO FOR LIFE!


    11 years ago on Introduction

    Good instructable.  Yours looks a bit more accessible.  I did some heater/blower work a few times on my 244 and it was a nightmare.