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 volvospeed.com - you might want to view that page too.

There's more info about Volvo 850 A/c & heating system at volvoclub.org.uk, 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.

Great write up, photos and annotations!<br>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!
hi, <br>thanks for the feed back. <br> <br>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. <br>i got a new core one month ago and now is working perfect again. <br>Volvo 850 SW TDI with 390.000 km <br>For me, the best car ever (for under 1500&euro;) <br> <br>thanks! <br>
<p>I have a Volvo 850 &quot;love it&quot;. 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, frankkazibwe@yahoo.com</p><p>Frank</p>
great instructable!<br><br>specially because you point out the screw that i was missing, the one inbetween the 2 pipes!!!! thanks so much<br><br>just one question:<br>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...<br>can i just bypass the core with a piece of hose connecting the 2 pipes?<br>i will loose heating but i will keep the coolant in his place (da engine), right?<br>will it interfere with any other thing?<br><br>good job
You could just put your temperature controls all the way to cold, that would prevent coolant from traveling through the heater core. <br> <br>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.
Sorry that my expertise/memory doesn't stretch to giving you a reliable answer on this ... can anyone else here help lobo0x7?<br><br>Dom
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.<br> <br> :O<br> <br> 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.<br> <br> 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.
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.
I recieved a &quot;Heater Pip line&quot; 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 &quot;heater hose&quot; itself. Are these the right parts?
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!
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.
Only 260,000 miles? I don't think this will be her last winter!
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.<br>Thank You VOLVO FOR LIFE!
I'm glad it was useful. :)
Good instructable.&nbsp; Yours looks a bit more accessible.&nbsp; I did some heater/blower work a few times on&nbsp;my 244 and it was a nightmare.

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