Understanding the Garrett GT37 Turbo Upgrade

Upgrading the turbocharger on a diesel engine is one of the most effective ways to unlock additional power and sharpen throttle response. Among the many options available, the Garrett GT37 stands out as a proven performer for a wide range of diesel applications—from light-duty pickups to heavy-duty work trucks. Its advanced aerodynamics, dual ball bearing design, and robust construction deliver quicker spool times and sustained boost across the rpm range.

This guide provides a thorough, step-by-step walkthrough for installing a Garrett GT37 turbocharger on a diesel engine. Whether you’re a seasoned diesel mechanic or an experienced DIY enthusiast, following these procedures will help you achieve a reliable, high-performance upgrade. Always reference your vehicle’s specific service manual and the Garrett installation instructions for torque specs and tolerance details.

Why Choose the Garrett GT37 for Your Diesel

The GT37 family—including popular variants like the GT3788VA and GT3794V—offers a blend of responsive low-end torque and top-end airflow that many other turbos in its class cannot match. Key advantages include:

  • Dual ball bearing center housing: Reduces friction for faster spool and improved transient response.
  • Billet compressor wheel: Lighter than cast wheels, providing higher flow capacity and better surge margin.
  • High-temp Inconel turbine wheel: Handles elevated exhaust gas temperatures common in tuned diesel engines.
  • V-band or T3/T4 flange options: Allows for flexible integration with existing exhaust manifolds and downpipes.

Many owners who have made the switch report noticeable gains in throttle tip-in and a broader power band without sacrificing top-end charge air delivery. For a deeper technical overview, consult Garrett’s official product documentation at Garrett Motion.

Tools and Materials Required

Before beginning the installation, gather the following items. Having everything on hand will minimize downtime and prevent mid-project trips to the hardware store.

Hardware & Consumables

  • Garrett GT37 turbocharger assembly (complete with actuator if equipped)
  • New exhaust manifold gaskets and turbo-to-manifold gasket
  • Oil feed and drain line gaskets or O-rings
  • Intake and intercooler hose couplers (if not reusing originals)
  • High-temp silicone sealant (rated for exhaust components)
  • Fresh engine oil and filter (use manufacturer-recommended viscosity)
  • Coolant premix (if your turbo is liquid-cooled)
  • Thread-locking compound (medium strength)
  • Penetrating oil for stubborn fasteners

Tools

  • Socket set (metric and SAE, including deep sockets)
  • Ratchet and breaker bar
  • Torque wrench (capable of ft-lb and in-lb ranges)
  • Combination wrenches
  • Screwdrivers (flathead and Phillips)
  • Gasket scraper or razor blade
  • Oil catch pan
  • Shop towels and brake cleaner
  • Safety goggles and mechanic’s gloves
  • Inspection mirror and flashlight
  • Vacuum pump or priming tool for oil system

Safety and Preparation

Working on a hot exhaust system or under a raised vehicle carries inherent risks. Follow these precautions to protect yourself and your equipment.

  1. Park on level ground and engage the parking brake. Chock the wheels.
  2. Disconnect the battery negative terminal to prevent accidental starting or electrical shorts.
  3. Allow the engine to cool completely—exhaust manifolds and turbo housings retain heat for hours. Use a touch test; if the manifold is warm to the touch, wait longer.
  4. Relieve fuel system pressure if your engine uses high-pressure common-rail injection (refer to your service manual).
  5. Use jack stands if you need to raise the vehicle; never rely solely on a hydraulic jack.

Removing the Old Turbocharger

The removal process will vary by engine platform (Cummins, Duramax, Power Stroke, etc.), but the general sequence remains consistent.

Step 1: Drain Fluids and Disconnect Lines

Place an oil catch pan under the oil drain line connection. Remove the drain line and allow residual oil to drain. Then disconnect the oil feed line at the turbo. If your turbo is water-cooled, drain the cooling system slightly to avoid spillage when removing the coolant lines. Label all removed lines to simplify reassembly.

Step 2: Remove Intake and Exhaust Ducting

Loosen the clamps on the intake tube between the air filter box and the turbo compressor inlet. Also disconnect the charge air duct (intercooler piping) at the compressor outlet. On the hot side, unbolt the exhaust downpipe from the turbine housing. If the downpipe is heavily corroded, soak the flange nuts with penetrating oil beforehand.

Step 3: Unbolt the Turbo from the Manifold

Support the turbo from below (use a jack with a block of wood if needed) while removing the mounting bolts or nuts that attach it to the exhaust manifold. Keep track of any washers or spacers. Carefully lift the turbo away from the manifold and set it aside. Inspect the old unit for any signs of oil leaks, shaft play, or wheel damage—this can help diagnose future issues.

Inspecting the Mounting Surface and Preparing the New GT37

With the old turbo removed, thoroughly clean the exhaust manifold flange using a gasket scraper and brake cleaner. The surface must be free of old gasket material, carbon deposits, and burrs to ensure a proper seal with the new turbo. Check the manifold for cracks or warpage. If warped, the flange should be surfaced or the manifold replaced.

Preparing the Garrett GT37

  • Inspect the new turbo for shipping damage. Rotate the compressor and turbine wheels by hand—they should spin freely with minimal resistance.
  • Apply thin coat of high-temp silicone sealant to both sides of the new manifold gasket (if recommended by Garrett). Do not over-apply; excess sealant can clog oil passages.
  • Pre-lubricate the turbo bearings by pouring a few teaspoons of clean engine oil into the oil inlet port. Rotate the shaft by hand to distribute oil—this step is critical to prevent dry-start damage.

Installing the Garrett GT37 Turbocharger

Installation is essentially the reverse of removal, but attention to detail determines long-term reliability.

Step 1: Mount the Turbo to the Manifold

Position a new gasket on the manifold studs, then lift the GT37 into place. Use a jack with a wood block to support the turbo’s weight while aligning the mounting holes. Install the nuts or bolts and tighten them to the manufacturer’s torque specification in a crisscross pattern. (Typical values: 30–45 ft-lb for M8 studs, but always verify with Garrett’s data sheet).

Step 2: Reconnect Oil and Coolant Lines

Attach the oil feed line using new copper or aluminum washers if provided. Torque to specification—over-tightening can crush or restrict the line. Connect the oil drain line; ensure it flows downhill from the turbo to the engine pan without any low points where oil could pool. For water-cooled turbos, reconnect the coolant lines and tighten clamps.

Step 3: Reattach Intake and Exhaust Ducting

Slide the intake tube and charge air hose over the compressor inlets/outlets and secure with clamps. Verify that all connections are tight, especially the intercooler piping. Reattach the exhaust downpipe using a new gasket (or high-temp silicone sealant) and torque the bolts to spec.

Post-Installation Checks and Priming

Before starting the engine, perform a final walk-through to catch any oversights.

  • Check all bolts and clamps for proper torque.
  • Refill engine oil to the correct level; if you drained coolant, refill and bleed the system.
  • Prime the oil system: disconnect the fuel injector harness or disable the engine crank sensor to prevent ignition (refer to service manual). Crank the engine for 10–15 seconds in 5-second intervals until the oil pressure gauge shows a reading. This pushes oil through the new turbo before it sees load.
  • Reconnect battery and restore any disabled systems.

Initial Startup and Break-In

Start the engine and let it idle at around 800–1000 rpm for 2–3 minutes. Do not rev it immediately. During this idle period:

  • Listen for unusual noises (whining, grinding, or air leaks).
  • Inspect all fluid connections for leaks. Use a flashlight and mirror for hard-to-see spots.
  • Monitor exhaust smoke. A small amount of white or light gray smoke is normal from residual assembly lube, but avoid thick black or blue smoke.

After idling, take the vehicle for a short test drive under light load. Vary engine speed without full-throttle runs for the first 50 miles to allow the turbo shaft and bearing to break in. This step is especially important for high-performance upgrades like the GT37. For detailed break-in guidelines, see Garrett’s installation knowledge center.

Throttle Response Gains and Tuning Considerations

One of the most immediate benefits you’ll notice with the GT37 is improved throttle response. The dual ball bearing cartridge reduces spool-up lag, so boost arrives sooner when you press the pedal. However, to fully realize these gains, your engine’s fuel injection timing, fueling rates, and boost control strategy must be calibrated. Consider these tuning topics:

  • Boost pressure targets: The GT37 can produce more boost than stock. Set boost limits in your tune to match the turbo’s compressor map (typically 25–35 psi depending on the model).
  • Wastegate or actuator control: If your GT37 includes an electronic or pneumatic actuator, verify that it opens at the correct pressure. Calibration tools can help set spring preload.
  • EGT management: Increased airflow can reduce exhaust gas temperatures, but aggressive fueling without enough airflow will raise EGTs. Install a pyrometer if you don’t have one.

For a deeper dive into diesel tuning with upgraded turbos, read this comprehensive guide from Diesel Power Products.

Common Pitfalls to Avoid

Even experienced installers can encounter issues. Watch for these common mistakes:

  • Forgetting to pre-lube the turbo: Starting a dry turbo can cause immediate bearing failure. Always prime with oil.
  • Using old gaskets or crush washers: Reusing sealing components leads to leaks. Always install new ones.
  • Cross-threading oil lines: Hand-start all fittings before using a wrench. Damaged threads are difficult to repair.
  • Incorrect wastegate plumbing: Boost creep or overboost can result from misrouted vacuum lines. Follow Garrett’s diagram precisely.

Ongoing Maintenance and Longevity

A properly installed Garrett GT37 will deliver years of service, but it requires routine care. Perform the following at every oil change:

  • Inspect intake and intercooler hoses for cracks or loose clamps.
  • Check the oil drain line for kinks or blockages.
  • Listen for changes in turbo whistle that could indicate bearing wear.
  • Replace engine oil and filter at intervals recommended for your vehicle with the turbo upgrade (more frequent changes may be needed for high-horsepower tunes).

For more information on turbocharger maintenance and diagnostics, refer to Engine Builder Magazine’s turbo maintenance tips.

Conclusion

Installing a Garrett GT37 turbocharger on a diesel engine is a rewarding project that transforms driving dynamics and power delivery. By following each step in this guide—from careful removal of the old unit to proper priming and break-in—you’ll achieve a reliable upgrade with noticeably sharper throttle response. Always cross-reference your specific vehicle’s service data and, if you encounter challenges beyond your comfort level, consult a professional diesel technician. The result is a diesel that responds to the throttle with newfound urgency and pulls harder across the entire rpm band—a truly satisfying outcome for any diesel enthusiast.