white exec wrote:
Simon, I think your recent theory about air ingress being worse at high pump speed is a plausible one.
In your case - where you have been plagued by repeated harsh running - I do have a question, though:
When it's harsh, are bubbles - of any size - visible (by dipping) in the reservoir fluid?
I haven't checked in quite a while but a couple of nights ago I got home from a 20 minute drive where the ride had started OK but got quite harsh by the time I came home. I took a photo just after I arrived home with the engine still running but had difficulty getting my phone to focus on the surface of the oil even with manual focusing, because it couldn't "see" the oil until the flash came on, so it kept focusing on the outside of the tank, but you can still see the bubbles:
Towards the top (the edge of the filter) you can see a few normal sized bubbles but the rest of the oil was absolutely full of loads of what we've now come to call "microbubbles"... bubbles that are about the size of a pinhead and presumably small enough to pass through the filters unhindered.
Some potentially very good news though - today I finally got around to replacing the leaking o-rings in the hydraulic pump - the top o-ring I changed in-situ a couple of months ago but the bottom one had started leaking more and more so I spent most of the afternoon taking the pump out and changing the two suspension/brake output piston seals and also the large seal on the power steering end cup.
I also had to replace the 50mm rubber joiner stub on the pump inlet hose, (unique to the V6 pump) as it was so hard and moulded to the shape of the spigot that it was impossible to remove it without it splitting on me. Luckily I had a piece of suitable hydraulic hose to replace it with. On reassembly I was extra careful with the clamping of the joiner stub to get the best possible seal, for example making sure that the bottom hose clamp was just past the bump on the spigot end rather than too far down.
I deliberately left the tank end of the inlet hose alone so as not to disturb the silicone I had previously added. I did have to remove the "mystery o-ring plug" though - turns out that its extremely useful for introducing a deliberate air lock so that when you disconnect the hose at the pump end it doesn't syphon the entire contents of your tank out all over the pump...
I did not re-silicone the mystery o-ring plug, just pushed it back in, for now.
After everything was back together I primed the pump with the bleed screw open, (to my surprise it self primed easily even though the entire length of inlet hose was full of air after reassembly) let it idle for a few minutes until the bubbles on the oil surface calmed down, closed the bleed screw, lifted the car right up and down once then back to normal height and went for a drive.
WOW.
The ride was absolutely fabulous.
No trace of harshness at all, also it did not seem to deteriorate at all over the period of the test drive, even though I was doing things to provoke it like heavy acceleration (causing lots of rear height corrector action) and using sport mode, causing the engine to be revving fairly high.
The ride was even better than it was when I first applied the silicone at the tank end all those weeks ago, I would go so far as to say that the ride was pretty much perfect - no harshness and riding about as smoothly as I have ever seen on a Xantia. At speed it felt extremely smooth and stable with a nice waft but with no pitching or wallowing.
When I got home again I checked the oil with a torch while the engine was still running - absolutely zero trace of microbubbles, just calm and still oil even though the engine was running.
In case anyone thinks its only riding better because of the inevitable de-pressurisation followed by Citrerobics in the course of doing the work, in the last few weeks I have been de-pressurising the car over night 2-3 times a week because of the temporary improvement in ride it gave, but it would always start to deteriorate again the more I drove the car, especially when driven multiple times in the same day.
Will the ride remain this good ? I don't know, lets see...
If it remains good, what was it ? Was it just the rubber inlet hose leaking on the pump, and possibly leaking worse when the pump got hot with engine heat ? A leak there would tend to leak oil when the engine was stopped, but suck air in when the engine was running.
Or could the leaking bottom o-ring have been a contributor ? I'd need to study the internal diagram of the pump again to work out whether that o-ring is always subject to pressure or whether it's subject to vacuum on a part of the pumping cycle.