Power Steering Pump Noise

Power Steering Cooler Flush for HD Trucks

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The cooler is often overlooked, but a clogged one ruins new pumps. Here’s how to inspect and flush it.

What the Driver Feels

  1. New pump overheats and fails within weeks
  2. Fluid runs too hot
  3. Pump whine gets worse after long highway pulls
  4. Return line feels hotter than normal
  5. Cooler has visible damage or blockage
  6. Fluid looks burnt even after a flush
  7. Pump pressure drops when hot
  8. Fleets reporting repeat pump failures

What Causes It

HD trucks have a power steering cooler (usually a small radiator in front of the main radiator) that keeps hydraulic fluid at operating temperature. Over time, the cooler becomes clogged with dirt, bugs, and internal varnish. A clogged cooler makes the fluid run hot, which thins it out and accelerates pump wear. On Freightliner Cascadia and Kenworth T800, the cooler is buried behind the grille and rarely inspected.

Fleets that install a new pump without flushing the cooler see repeat failures within 50,000 miles. The old pump shed metal particles that are trapped in the cooler — the new pump pumps this debris right back through itself.

How to Inspect

Safety: Let the truck cool completely before touching cooler lines.

1. Locate the power steering cooler — usually a small aluminum radiator near the main radiator or AC condenser.

2. Check for external blockage (bugs, dirt, debris). Clean with low-pressure water.

3. Disconnect the return line and flush with fresh hydraulic fluid until it runs clear.

4. If flush doesn’t clear, the cooler is internally blocked — replace it.

5. Check the cooler lines for softness or swelling.

Recommended Repair

  1. Always flush the cooler when replacing the pump.
  2. If the cooler is internally blocked, replace it — it’s cheap insurance.
  3. Clean the external fins every spring (bug season).
  4. Replace the return line filter if equipped.
  5. After service, monitor fluid temperature for the first 1,000 miles.

Send us your VIN or OE number to get a fast wholesale quote on a replacement power steering pump. We stock new and reman pumps for passenger cars and heavy-duty trucks.