Cummins ISL Turbocharger Guide: HX40W, HE431V & HE400VG by Engine Version

This Cummins ISL turbocharger guide answers the first question on any ISL turbo job: which Holset is on this engine? The 8.9-liter ISL has been built since the late 1990s for transit buses, motorhomes, fire apparatus and vocational trucks, and across those years Cummins fitted it with both wastegated and variable geometry turbos. Order by the engine’s data plate and the number on the turbo’s tag, never by “ISL” alone.

Which Turbo Is on a Cummins ISL

These are the turbochargers PT Turbo lists for the ISL and its close relatives, the export ISLe and the off-highway QSL, with a part number for each.

Turbo	Type	Listed for	Example part number
Holset HX40W	Fixed geometry, wastegated	ISL, ISLe, QSL and the 8.3L ISC, including coach and transit bus versions	4033569H, 4033391H
Holset HE431V and HE431VE	Variable geometry	ISL and ISLe with exhaust gas recirculation	4040234H, 5456013H
Holset HE400VG and HE300VG	Variable geometry	Later ISL ratings	4036850H, 5327351H
Holset HE400WG	Fixed geometry, wastegated	ISLe	4033169H

Two points follow from the table. The wastegated HX40W, not the HE400WG, is the turbo most ISL listings carry. And an ISL with exhaust gas recirculation has a variable geometry turbo, which is a different job to diagnose and a different part to buy. If your number is not on those pages, send us the tag numbers and we will cross it.

Wastegated or Variable Geometry: How to Tell

Look at the turbo. A wastegated HX40W or HE400WG has a small pneumatic canister on the compressor housing with a rod running to a lever on the turbine housing. Boost pressure pushes the rod, the wastegate opens, and excess exhaust bypasses the turbine.

A variable geometry ISL turbo has no wastegate. Instead it has an actuator on the bearing housing: an air-operated one on the HE431V of the EGR engines, an electronic one with a wiring connector and coolant lines on the HE431VE. Holset variable geometry turbos use a sliding nozzle that the actuator moves across the turbine inlet. That gives quick boost at low speed, drives exhaust gas recirculation and works as an engine brake. It also adds two things that fail: the nozzle, which soot can bind, and the actuator. For the operating principle, see the variable-geometry turbocharger overview; our Cummins ISB 6.7L guide covers how the Holset design behaves in service.

Common ISL Turbo Failure Symptoms

Symptom	Wastegated turbo	Variable geometry turbo
Low power, slow boost build	Wastegate stuck open, weak actuator spring, boost leak	Nozzle stuck open, actuator fault, boost leak
Overboost, surging	Wastegate stuck shut or actuator hose off	Nozzle stuck closed
Fault codes for the turbo actuator or turbo speed, derate	Not fitted	Actuator wear, sooted nozzle, speed sensor fault
Weak engine brake	Not turbo related	Nozzle not reaching the closed position
Blue smoke, oil in the charge piping, shaft play	Worn bearings and seals on either type

Bus and refuse duty is hard on any turbo: constant stop and go, long idling and hot shutdowns. Check shaft play by hand and pressure-test the charge air system before ordering parts. A turbo that is not building boost is often a split hose or a leaking charge air cooler.

Replacement and Rebuild Options

Option	Price	Notes
New Holset HX40W for the ISL	$1,239 to $2,353 (25 listings) at PT Turbo	Match the part number to the engine
New Holset HE431V or HE431VE	$4,280 to $6,223 (7 listings) at PT Turbo	Variable geometry; an electronic actuator (HE431VE) has to be calibrated to the turbo
New Holset HE400WG	$654 to $2,920 (19 listings) at PT Turbo	ISLe and other engines; see the HE400WG guide
Rebuild your own turbo	From $575 at PT Turbo (price list)	For a unit with sound housings and wheels

Price ranges in this article are general estimates to help with budgeting, not PT Turbo quotes. Our current prices are on each product listing, and our rebuild prices are on the turbo rebuild price list.

A new variable geometry turbo for the ISL costs several times what a wastegated HX40W does, which is why a rebuild is worth pricing on those units. Our turbocharger rebuild service is a mail-in service: we inspect the turbo and confirm the price before any work starts, VSR balance every rebuild, and back it with a 12-month unlimited-mileage warranty. Turnaround is 3 to 5 business days after inspection. PT Turbo has been in the turbocharger business since 1978 and stocks both new and remanufactured turbochargers.

Installation and Maintenance

• Find the cause first. Oil starvation, a restricted drain, debris and soot each leave their own marks on the old turbo.
• Use new gaskets and torque the mounting hardware to specification. Reused gaskets are the usual source of oil and boost leaks after a turbo job.
• Replace or clean the oil feed and drain lines, change the oil and filter, and prime the turbo with clean oil before the first start.
• On a variable geometry turbo with an electronic actuator (HE431VE), run the actuator calibration with the engine maker’s service tool after the install.
• Keep the air filter and charge air cooler clean, and let the engine idle briefly before shutdown after hard work.

Running other engines in the fleet? Our full list of turbo guides covers the ISB, ISC, ISM and ISX and the common Detroit, Volvo and PACCAR engines.

Frequently Asked Questions

Which turbocharger fits the Cummins ISL 8.9L engine?

It depends on the engine version. PT Turbo lists the wastegated Holset HX40W for many ISL, ISLe and QSL engines, the variable geometry HE431V and HE431VE for ISL engines with exhaust gas recirculation, the HE400VG and HE300VG for later ratings, and the HE400WG for the ISLe. Match the number on your turbo’s tag.

Does the Cummins ISL have a variable geometry turbo?

Engines with exhaust gas recirculation do: a Holset turbo with a sliding nozzle, moved by an air-operated actuator on the HE431V and an electronic one on the HE431VE. Earlier and export engines use a wastegated turbo such as the HX40W.

Can a Cummins ISL turbo be rebuilt?

Yes, when the housings and wheels are sound. A rebuild renews the bearings and seals and balances the rotating assembly, and on a variable geometry unit the nozzle is cleaned and freed. Rebuild prices are on PT Turbo’s price list, and the price is confirmed after inspection, before any work starts.

Further reading: Learn more about turbocharger technology.