'09 XC70 Hydro Tailgate -- intermittent opening AND closing (on my head) Topic is solved

lropeik · Post by **lropeik** » 06 Mar 2019, 13:23

My first post for my beloved 2009 XC70 T6/3.2 Polestar! Thanks in advance.

Tailgate is intermittent--in both directions! Note: it isn't a stuck latch, because I CAN always open it by hand in the half-second when it's trying to open itself.

1. Occasionally it will open fine (both with fob and from dash), but more often it whirrs, clunks, and pushes off the bumpers--but just 1/2" or so, and then it closes itself up again.

2. When it does get open (manually or by fob/dash), it usually starts to close on me; most often slowly, but sometimes it stays up all by itself. I've got my rubber-tipped pole to hold it open, but its' time to FIX it.

Bad lifting cylinder (just the one, I think)? Hydraulic pump needs fluid (or $$--worse)? Misadjustment/misalignment of the bumpers at left and right near tail lights?

Doesn't seem to be temperature-related, BTW.

Ideas welcome.
thanks

Larry R

Post by **jimmy57** » 06 Mar 2019, 15:22

If the cylinder is the issue it would most likely be an issue all the time once the piston seal failed. The start would be fluid level check. On that car the pump should be in left quarter behind the wheel up high. The solenoid on the pump assembly could have some little piece of debris that sticks it open. While you are there you should remove the solenoid and clean it with WD-40 or similar spray and then blow it out. Even better is to energize it and blow it out. Use towels and prop tailgate to minimize loss of oil. The oil is Pentosin CHF-11S. Napa has or can get it. Use suction and drink straw with rubber hose to get the old fluid out for a fluid change.

lropeik · Post by **lropeik** » 06 Mar 2019, 15:35

Wow. THIS is why you join forums. I've wondered about the oil, and you've given me the info and the confidence to have at it. Thanks so much for your detailed reply!

Post by **jimmy57** » 06 Mar 2019, 16:20

little tidbit: the solenoid opens the fluid flow path to and from cylinder. The pump motor runs CW and CCW to determine whether it goes up or comes down. The flow reverses "polarity" and that determines whether the cylinder gets fluid applied to base to extend and open which sucks fluid from rod end. When it comes down the rod end gets pressure to push piston towards base pulling rod in and suction is applied to base. The cylinder has to pull tailgate down against that other gas strut and it gets it to near latched position. WHen the latch contact switch closes the pull-in motor draws a cable in to close the latch. The hydraulic strut has very poor leverage to close the tailgate and make it latch without that closer motor action.

lropeik · Post by **lropeik** » 06 Mar 2019, 17:45

Love it. Thanks--I never met a solenoid that wasn't at the heart of things.

lropeik · Post by **lropeik** » 04 Apr 2019, 07:50

Jimmy57 (et al),
I refilled the almost-empty hydro oil and it's working much better--thanks again. But it still closes on me -- not real fast, but about 50% of the time. (and it's till balky opening first thing in the a.m.
My questions:
Am i now looking at a bad pump--letting oil back into the reservoir?
Or a bad / leaking cylinder (though a leak would not be intermittent)?
And am i right that there is no second (non-hydro) cylinder on the other side?

Thanks.

Post by **jimmy57** » 04 Apr 2019, 10:10

There is only the one cylinder with the normal hydraulic/gas one on the other side.
It is possible to have a cylinder seal that is intermittent. I have not seen it on that system but I have seen it on some hydraulic convertible tops. If the seal hardens it can fail to contact the cylinder and the oil goes by. If the seal happens to catch the oil and it pushes against the cylinder then it works. Did you find oil somewhere to show where it leaked out?

lropeik · Post by **lropeik** » 04 Apr 2019, 10:18

that's the thing--no leak (at least none showing through the headliner, along the lines or in the pump housing/area).

BTW, when I filled the oil I did it with the tailgate open--i.e., with any remaining fluid in the lines, figuring that meant maximum room in the pump reservoir for the new oil.

One last symptom, if i never mentioned it--it always clicks/releases at the catch and pops out the centimeter or two, but sometimes it stops there (no lifting) and then recloses.

I really appreciate your interest.

Post by **jimmy57** » 04 Apr 2019, 16:59

There is an assist motor and cable the finishes the close of latch and begins the opening due to the hydraulic cylinder having poor leverage when the tailgate gets down. What you see is expected if the hydraulics don't take over once the latch open/close assist step completes.

lropeik · Post by **lropeik** » 10 Apr 2019, 12:28

Hey, thanks. When my back spasms calm down, looks like I'll be doing some serious hydro-oil-line fault-tracing! LR