Global Machinery Company Sierra 1999 - Manual (Page 330)

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Power Steering Fluid
When to Check Power Steering Fluid
It is not necessary to regularly check power steering
fluid unless you suspect there is a leak in the system or
you hear an unusual noise. A fluid loss in this system
could indicate a problem. Have the system inspected
and repaired.
How to Check Power Steering Fluid
When the engine compartment is cool, wipe the cap and
the top of the reservoir clean, then unscrew the cap and
wipe the dipstick with a clean rag. Replace the cap and
completely tighten it. Then remove the cap again and
look at the fluid level on the dipstick.
The level should be at the FULL COLD mark. If
necessary, add only enough fluid to bring the level up to
the mark.
What to Use
To determine what kind of fluid to use, see
“Recommended Fluids and Lubricants” in the Index.
Always use the proper fluid. Failure to use the proper
fluid can cause leaks and damage hoses and seals.