Why do SZ-series Rolls-Royce and Bentley hydraulic reservoirs leak when the cars sit?

This article applies to: SZ Series Rolls-Royce and Bentley – 1981-1999 Silver Spirit, Silver Dawn, Silver Spur. Bentley Mulsanne, Eight, Brooklands, Turbo R and variants. 1992-2003 Continental and Continental R / T / S / SC. 1996-2003 Azure. 1981-1995 Corniche.

An older Rolls-Royce or Bentley may be leak-free all season when it’s driven regularly, but when it’s put away in the fall, and sits for a week or so, you may see a pool of hydraulic oil on the ground inboard of the left front tire. What’s wrong, you ask?

Usually, the rear springs have gotten weak with age, and the hydraulic suspension has leaked down. The weak springs put too much weight on the hydraulics, and that pushes hydraulic oil out of the shocks as the car settles. The oil slowly makes its way past the height control valves in back, and flows into the reservoir under the hood, behind the left front wheel.

Eventually, the reservoir can’t hold any more fluid, and the excess ends up on the ground.

When you look at the car, the rear will generally be sagging low. If you start the car, the hydraulic pumps on the engine should push oil back into the shocks, and the car should lift back to its normal height.

Now that the excess oil has been dumped on the ground, there may be a new problem. Once the car has leveled itself, you may see a warning for low mineral oil, or the lamp may simply say: BRAKE.

If you’re going to drive the car regularly, feel free to add oil to get the light to go out, but bear in mind that you’ll go through this exercise again if the car is left sitting and the oil you just added gets pushed out onto the floor.

What can you do about that?

At Robison Service, we have started adding shims (a factory-approved procedure, BTW) to prevent the car from sagging so low when there is no hydraulic pressure. If there is not room to add enough shims, new rear springs may be needed.

I believe this is the best fix. Other people suggest putting wood blocks under the car to prevent settling, but I don’t like that because you may forget about the blocks, try and drive the car, and cause damage.

Other people avoid this issue by storing their cars with the wheels hanging, on a lift. This has the benefit of preventing flat spots from developing in the tires, but it has a hazard you may not expect: Shock absorbers that are left dangling for months sometimes burst a seal and fail when the car is put back on its feet, and we see shock fairly fairly often now that these cars are 30-40 years old.

These hydraulic systems use traditional green mineral oil, referred to as HSMO or LHM. Do not mix motor oil or transmission fluids in these systems, and never put DOT 3 or DOT 4 brake fluid in them.