RWD - Revenge of the 940 -Heater valve and heater hose

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Revenge of the 940 -Heater valve and heater hose 900

You folks are going to love this...

So yesterday I write a long post here in reply to OnlyVolvo regarding mysterious cooling system problems in a 940. No special reason for my post, just thought I was able to give some added insight into someone's problems based on my related experiences last year. So in that post here and relating my tales, I clearly insulted my wife's 940 for its age and all the problems it gave me last year (constantly begging for my attention, the selfish beast, I mean the car). Now this car is garaged side by side with my 940T. It's now quite apparent they must have been talking last night. Today, an hours highway drive from home, my 940T decides to let go the heater valve in revenge. I mean, really, what are the odds of that happening within a day of my posting?

Now fortunately this was in a Walmart parking lot and I was able to go in and grab a jug of antifreeze, on sale no less, and limp home. The giveaway that made me go looking behind the engine at the heater valve wasn't a slowly dropping reservoir in preceding days, or steam under the hood or out from back under the car, or fluid running on the ground, or even the temp needle rising. The first symptom was the electric fan running on after shutdown (note this can only happen in 940s, not 740s where the electric fan can't get power when the ignition switch is off). I first thought it was a sticky fan relay as the temp needle was fine and I'd checked the coolant level within the past month. While under the hood trying to pull the connector off the fan relay to shut it off when I was parked, that's when I noticed the expansion tank was stone empty. Parts are now ordered (including a new inlet hose that split while I was taking the valve out to do a temporary fix). All should be back to normal by tomorrow. I'm just thankful my 940T did not decide to take out the heater core in revenge (I've done the core in that car once already, so it knows how much cussing I can do at it when I'm really disappointed with it).

So, additional lessons learned today:

1) Never trust an old heater valve, especially if it's spent half its life all greasy, and most certainly if it hasn't been replaced in living memory. I can't count the number of times we've all been warned here on the brickboard (Spook). Go in there, grab the valve in one hand and give the hose connections at each end a bend in all directions to test the integrity of the plastic necks (which is where they break). If a valve neck breaks off, you just saved yourself a potential breakdown when you least want it.

2) Add to your car toolkit some hose plugs so you can do a decent temporary fix if your heater valve ever breaks, or if one of the heater hoses splits, or if the heater core should fail!!! In my heater core FAQ writeup I recommended using 1/2" copper plumbing fittings to do a bypass and couple the hoses together. I have since found a better and more universal solution which is not to have a wide open heater hose loop, but rather to block flow completely. Rummaging around in my plumbing box, what I've now found perfect for the job is a male 5/8" NPT threaded plug (cast iron, galv, brass, copper, plastic, whatever) available from your local plumbing store. With the ring clamp loosely in place, thread the plug into the hose as far as you can just leaving enough of the square end exposed for removal. Put the hose clamp on near the very edge of the hose so it makes a positive fit over the threads. You'll need two of these plugs, one for each hose you cut/remove. At the same time, get a 3/4" NPT male plug. If you have to cut the lower heater hose at the bends, you will likely need 3/4" there, not 5/8"

3) Never insult your brick. Over time, old Volvo's seem to develop a psychic ability to know what would piss you off at the most inopportune time. An old Volvo saying used to be, "Drive 'em like you hate 'em." (I think that was even in a Volvo advertising campaign a few years before they stacked a bunch of 140s on top of each other to prove body strength -good back story on that ad if you do some research). With almost 50 years of Volvo ownership now under my belt, I've come to learn that RWD Volvos can tolerate a lot of mechanical abuse (with the exception of B234F timing belts), but maybe not so much emotional abuse!

Bonus notes for those reading this far down:

At the same time as replacing the heater valve, expect that the lower block outlet heater hose (from the block to the lower end of the heater valve) will be gummy on the bottom of the bend and ripe for splitting open during handling. Having had these split open twice during handling, I would recommend a new hose with each new heater valve unless they're in pristeen condition -they're not that expensive. This hose between the block and the heater core inlet often comes as one piece that you cut in two to insert the heater valve. The existing upper hose section to the heater core will often still be in good shape, so if you want to skip replacing the upper hose in order to save time fussing getting it off the heater core nipple then that's fine by me.

As another note, the original Volvo heater valves with the metal diaphragm section, are seemingly no longer available. The new Volvo one is all plastic and to my eye is identical to the Pro Parts Sweden heater valve which is far cheaper. I've seen aftermarket MTC heater valves that look just like the original Volvo, but they fail in exactly the same way. The very different looking Four Seasons aftermarket heater valves (under various jobber brand names) are nowhere near as good IMO and may also have vacuum hose fitment issues. There is also a small Volvo adapter vacuum hose that is sometimes suggested, but so far I haven't needed it, worst I've ever had to do was pull off the rubber nipple on the vacuum hose and turn it the other way round.

Let's keep 'em rolling!
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now


New 3 Revenge of the 940 -Heater valve and heater hose [900]
posted by  Dave Stevens  on Wed Apr 3 20:45 CST 2019 >

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