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Cummins ISX Signature 600 turbo HX55W 4046127 front view

HX55W 4046127 Turbocharger for Cummins ISX2 Signature 600

HX55W

The HX55W is the Holset turbocharger for the Cummins ISX2 and ISX Signature 600 engine — the 600 HP top-of-the-line ISX before VGT turbos took over. The W in the model name stands for water-cooled: the bearing housing on the HX55W has coolant passages in addition to oil cooling, which is critical at the higher exhaust temperatures the 600 HP rating generates. This is a fixed-geometry turbo with no electronic controls, no VGT vanes, and no wastegate. It also fits QSX15 applications. This is not the same turbo as the HX55 (4089754) used on the Signature 450 — that unit is oil-cooled only. Our HX55W is built new with all new components, dynamically balanced, and ships with gaskets. We supply shops, fleets, and distributors.

Turbo Model

HX55W (water-cooled, fixed geometry, non-wastegated)

OEM / Interchange Numbers

4046127, 4090042, 4046132, 4046131, 4037480, 3800774, 3800890, 4024854, 4025321, 4036758

Application

Cummins ISX2 / ISX Signature 600, QSX15 (2001-2014)

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FAQ

The HX55W (4046127 / 4090042) fits the Cummins ISX2, ISX Signature 600, and QSX15 engines. Production years run from 2001-2014. Common applications include Kenworth, Peterbilt, Freightliner, and other Class 8 trucks running the 600 HP ISX rating.

W stands for water-cooled. The bearing housing has coolant passages in addition to oil lubrication. At 600 HP, exhaust temperatures are too high for oil cooling alone — the coolant passages protect the bearings from heat damage and oil coking.

No. The HX55 (4089754) is oil-cooled only and fits the 450 HP Signature rating. The HX55W has a water-cooled bearing housing and fits the 600 HP rating. They have different bearing housings and are not interchangeable.

No. The HX55W is a fixed-geometry turbo with no wastegate, no VGT, and no electronic components. Bolt on, connect oil and coolant lines, and go.

Brand new, 100% new components, dynamically balanced. Ships with gaskets. No core charge. One-year unlimited-mileage warranty.

Yes. US stock, volume pricing for shops, fleets, rebuilders, and distributors.

HX55W for Cummins ISX Signature 600: Water-Cooled Turbo for the Top-HP ISX

The Signature 600 was the flagship ISX rating — 600 HP from a 15.0L inline-six. At that output, exhaust gas temperatures are high enough that an oil-cooled-only turbo bearing runs too hot. The HX55W solves this with coolant passages cast into the bearing housing. When replacing this turbo, you need to reconnect the coolant lines — something the oil-only HX55 does not have.

HX55W (600 HP) vs HX55 (450 HP) — key differences

FeatureHX55W (this page)HX55
Bearing coolingOil + water (coolant passages)Oil only
EngineISX2 / Signature 600, QSX15ISX1 / Signature 450
HP600 HP450 HP
Key part #4046127 / 40900424089754 / 4036892
Coolant linesYes — two connections on bearing housingNone

The coolant lines are the quickest visual identifier. If your old turbo has two coolant hose fittings on the center section, you have the HX55W. If it is oil lines only, you have the HX55.

Why water cooling matters at 600 HP

At 600 HP, exhaust gas temperature (EGT) at the turbine inlet can run significantly hotter than on the 450 HP rating. Oil alone loses its cooling capacity at these temperatures — it breaks down faster and forms coke deposits inside the bearing housing. The coolant passages in the HX55W draw heat away from the bearing area, keeping oil temperature within its working range. This is why many Signature 600 trucks get more turbo life than you might expect despite the higher output — the water cooling makes a real difference.

Common failure modes

  • Coolant leak at bearing housing — the coolant O-rings or fittings on the bearing housing degrade over time. Coolant leaking into the bearing housing contaminates the oil and accelerates bearing wear. Always replace the coolant fittings and O-rings when installing a new turbo.
  • Bearing wear — still the most common overall failure, especially when coolant leaks go undetected and contaminate the oil.
  • Turbine housing cracks — the higher EGT accelerates thermal fatigue on the twin-scroll housing.
  • Oil coking — shutting down a hot 600 HP engine without an idle-down period cooks the oil in the bearing housing. Always idle for 3-5 minutes before shutdown.

Installation

  • No electronics — bolt on, connect oil lines and coolant lines, start the engine.
  • Replace coolant O-rings and fittings at the bearing housing. Do not reuse old seals.
  • Flush the oil feed line. Replace the oil drain gasket.
  • Fill the coolant system and bleed air before startup.
  • Prime the turbo with clean oil, hand-spin shaft, idle 3-5 minutes before loading.

See our quality process for details.

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