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XC90 '02–'15 General Forum for the P2-platform XC90 model |
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Gear box oil change.Views : 3572 Replies : 41Users Viewing This Thread : |
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Dec 3rd, 2019, 18:22 | #38 | |
Bungling Amateur
Last Online: Yesterday 20:51
Join Date: Aug 2014
Location: Beverley, East Yorks
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1 - The old oil is so saturated with deposits that it will not absorb any more and hence debris accumulates in parts of the gearbox. When the fluid is changed, the new clean fluid penetrates the debris accumulations and loosens it in lumps which can lead to blockages and sticking valves. This can be mitigated by doing it in 3 or 4 partial changes (aka sump dumping) with a few hundred miles between them. 2 - The difference in viscosity between the oil and new fluid is so great, the gearbox electronics do not adapt quickly enough and an old fragile box is further damaged by shift shock etc. as it re-adapts. This can be mostly mitigated by clearing the adaptation memory or (even better) re-adapting the gearbox after changing the fluid. Where a gearbox is worn and has very old fluid, changing it can exacerbate certain faults due to the thinner fluid leaking through out of tolerance parts but this is really only a risk if the gearbox is knackered anyway. Even those owners with faulty gearboxes who change the fluid usually report noticeable improvement in spite of the underlying problems not being fixed.
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