Condition: your windscreen washers barely spray any water at all, in spite of the windscreen washer reservoir being full. You've already referred to page 162 of your owner's manual to unblock the jets, but still no joy.
You've also referred to page 174, and noted that you've only used approved washer fluid. Or perhaps you haven't... However, the manual only states that 'non-approved fluid may adversely affect the wiper blade rubber, resulting in ineffectual and noisy wiping' (side note: you know you've bought a premium luxury car when the manual writer lobs in the word 'ineffectual'). It says nothing about the toxic sludge that is generated if you live in a country where you don't need to use the washers sixteen times a day.
If you've been acutely observant, and have bi-xenon headlamps, you will have noticed also that you need to be travelling at approximately 200kmh to get enough water onto the windscreen via the deflection generated from the headlamp washers, which work perfectly. You're now puzzled as to why Jaguar thought that this was the best way to clean the windscreen.
There are two pumps hanging off the windscreen washer reservoir: one for the windscreen, and one for the headlights. The windscreen pump sits at the bottom of the reservoir, whilst the headlight pump sits above this, out of harm's way. Over time, the windscreen pump filter - which is designed to stop leaf matter, goldfish, shoelaces and contact lenses from becoming macerated by the pump - becomes clogged by a festering conglomeration of goo and other sticky residue. A simple by-product of the stuff that you put in your windscreen washer reservoir to allegedly make windscreen cleaning more effective. Left unattended, the goo becomes thick enough to clog the filter entirely, and no amount of hot water or complete flushes of the system will unblock the filter - or the hoses that lead to the wiper arms.
What to do? Very simply, you'll need to set aside about 30 minutes to resolve the problem with a very basic tool kit, or you can wander off to the dealers and ask them to fix it for an hour's worth of their time (as the invoice will show).
Compressed air (from compressor or can)
Large flat bucket (20 litres)
12-volt power supply for testing purposes
Short length of 7mm inside diameter plastic hose
An ability to tolerate getting wet
Here's the plan of attack in basic steps:
1. Check that the filter is clear and unblocked
2. Make sure that the pump works
3. Check that the hoses are clear and unblocked
4. Make sure that the reservoir is full of clean water (and nothing else).
Put the car on level ground and in Park, handbrake on, put chocks around the passenger side rear wheel, loosen (but not remove) the driver's side front wheel nuts, and use a trolley jack in the designated spot under the driver's door to lift the car just enough to make the front driver's wheel leave the ground. The cautious amongst us will suggest that you need to block up the vehicle with a stand or bricks etc, but the work that you're carrying out here does not involve getting under the car at any time.
Remove the wheel nuts and the wheel, set aside for later (you could spend the rest of the day cleaning and waxing the inside wheel rim if you're super keen).
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You've got two choices here: if you've done this before, you'll take the short path, but if it's your first time, take the long path. The short path is to remove the fixing screws and bolts for the rear of the inside plastic wheel arch liner and prise it back enough to access the reservoir. However, the longer path is not much longer, and makes the operation easier to manage. Here's the long path:
At the rear of the wheel arch liner, there are two Phillips-head screws, and two 10mm bolts, plus another screw facing you near the suspension parts. Remove these, noting that the plastic washer assembly behind the screw must be prevented from rotating, as it forms a locking collar to hold the plastic wheel arch liner against the wheel arch itself.
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Now move to the front of the wheel arch liner, where there are four 8mm bolts, and another Phillips-head screw to remove. Set these aside somewhere safe, and then remove the wheel arch liner, noting that it is hooked behind a metal plate near the suspension arm, and also tucks into the top of the wheel arch.
You'll see the reservoir clearly now, directly under the filler cap for the reservoir. One pump is strapped to the side of the opaque white reservoir, whilst the other is mounted at the bottom. We're interested in the bottom one.
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Grasp the bottom pump (it's black, with a grey band around the middle) and pull to the front of the car. It will release itself from the bottom of the reservoir, and you'll be left holding the pump with a black hose and wiring. Remove the wiring by disconnecting the connector (a small protrusion at the top of the connector must be depressed to release the catch). Whilst you're at it, remove the black hose by pulling it away from the pump unit. Set the pump aside for now, since you're probably cursing that I didn't warn you about the release of water from the reservoir drenching you with washer fluid, and spraying itself all over the disc brakes.
But you might be lucky - the filter in the bottom of the reservoir might still be in place, and gummed up so much that no water is released. Nonetheless, you're about to get wet (this is where the flat bucket comes in handy, and possibly if you have some 25mm hose, this can be put to good effect, too, by redirecting the water that is about to gush from the reservoir).
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Remove the filter/plug from the bottom of the reservoir. If you've planned ahead by reading all the instructions first, you will have siphoned off the water in the reservoir first, but where's the fun in that? Besides, I did this on a hot day, and the soaking was much appreciated.
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The filter will, no doubt, look as though it's been in the London sewers for thirty years. It'll need a clean. Be gentle, though, as whilst it is very flexible and rubbery, you don't want to either damage the filter or the seal that it forms when plugged back into the reservoir casing. Here's what it looks like when it's healthy.
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And here is a picture of where the pump and filter sits - make sure that there is nothing lounging about in the bottom of the reservoir.
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That's the filter all sorted. Now to be sure that the sludge hasn't decided to migrate up into the hoses. We should be thorough here and make sure that the pump works, but let's get back to that in a moment. Okay, so the black flexible hose that you've disconnected from the pump leads up to the windscreen washer arms.
If you've got the lungs of a Welsh opera singer, then by all means have a crack at blowing through the hose to see if air will escape onto the windscreen. However, if you're like most people, lung power won't be enough. Grab a bottle of compressed air (or fire up your compressed air generator, which every good home mechanic will have) and attach the black hose to the air. Let fly and see what comes through.
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More than likely, some of the sludge will have found its way into the hose, so a few squirts will be needed to clear the lot. You might even need to refer back to page 162 of the manual to unblock the jets (this is important). So you've now ensured that a) the filter is now squeaky clean, and b) that the hoses are clear.
Last job is to check the pump. This is where you'll need a supply of 12 volts DC, and some water - it's best to test pumps that pump water with real water. Attach a short length of hose to the outlet, and put sufficient water into a small bucket or bowl to immerse the pump, but not the wiring connector. Attach 12 volts to the pump (anything from 4.5 volts upwards will do, and the pump won't mind if you wire it up with reversed polarity, so long as you're ready to switch it the other way once you discover that it isn't working properly).
The reason for attaching the short length of hose is to demonstrate that water is actually being pumped (the motor might make a noise, but it might have broken the impeller, which means that the motor will run, but no water will pump). Once you hear it pumping away, lift the hose and see if water is being propelled through the system. If not, reverse the polarity of the terminals of the power supply and try again. If it pumps water out through the hose, you know it works. All good and ready to reassemble.
End result: you've cleaned the filter, you've cleared the hoses, you've checked the pump, and you've now got a reservoir that is empty of water. But it might still have more sludge in the top, or even in the bottom. Next step is to find some hot water (not boiling, but as hot as you can handle), and pour it through the reservoir. Ideally, you'll have 20 litres of hot water to do this thoroughly, since there is a small ledge near the top of the reservoir which might have attracted some sludge, and the only way to dislodge this (without removing the reservoir completely) is to fill the thing a few times.
Did I mention that it would be handy to have a hose leading out of the reservoir to a flat bucket at this point? If not, at least your floor will get a good wash. I was less fortunate, since my Jaguar sits in a carpeted garage (it is a luxury vehicle, after all). However, the temperature outside is well above 30 degrees, so it'll dry out soon enough.
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Inspect the reservoir closely to make sure that it's clean, and move to reassembly time. Now is not the time to get too enthusiastic, though - as I discovered when I replaced the filter, and then reattached the pump, thereby pushing the filter into the bottom of the reservoir. Incidentally, if you do exactly what I did, it's not impossible to recover the filter, and it makes the beer that you're going to have at the end of the day even more worthwhile.
The trick here is to reattach the hose and wiring connector to the pump, and to then place the filter on the pump, THEN push the whole assembly into place. Since you've got the inner wheel arch liner off, you might as well clean out the grunge, gunk and silt that has collected just below the pump and in the undertray of the vehicle, since you'll not be seeing it again for some time. Once sparkly clean, you're ready to reattach the liner with the bolts and screws, noting how the liner slots into place.
I'll be confident here and suggest that since you've tested all three component parts carefully, then there is no need to fire up the washer to see how it goes before the liner is reattached. But if you do decide to be cautious, and need to test the whole operation (perhaps it was a fuse, you are thinking), you'll need to put water back into the reservoir (sludge-free water only), and remember to put the bonnet down unless you want to watch the wiper arms attempt to reshape the trailing edge of the bonnet.
Don't forget to put the front wheel back where you found it, and remove the chocks that you put in place to stop the car wandering off. Refill the reservoir to the top with sparkling fresh sludge-free water, and promise to remember not to use additives in future. Remind yourself that a bit of Rain-X or similar on the windscreen would be a good idea, if only to avoid using the washers in future. Put your tools away, return the hose to the back of the aquarium, and return the trolley jack to your neighbour.
After all that labour (30 minutes, tops), it's now time to step back, admire your work, grab a beer or other refreshment, and return to normality, where windscreen washers actually work when you want them to.
PS. It took me longer to write this up than do the work, if that's any consolation!