Audi B8/B8.5 S4 Water Pump and Thermostat: Supercharger-Off Repair

Bottom line: A full Audi 3.0T cooling repair covering bumper service position, supercharger removal, thermostat and pump sealing, belt routing, supercharger resealing and controlled coolant bleeding.

Repair at a glance

Field	Repair detail
Applies to	Documented 2013–2016 S4 and 2013–2017 S5 3.0T layout; verify earlier/later variants
Repair trigger	Proven pump leak, thermostat circuit/mechanical failure or overheating cause
Parts	Pump, thermostat, crossover O-rings, manifold seals, coolant and inspected belts
Time / difficulty	Full day; advanced due to front service position and supercharger removal
Stop point	Overheating damage is suspected or supercharger cooling circuit cannot be bled correctly
Proof complete	Stable temperature and heat, dry pump/pipe interfaces, no air or thermostat fault

Confirm the repair before disassembly

Pressure-test the engine cold and inspect the pump weep path, thermostat housing, crossover, reservoir and supercharger coolant connections. A sweet odor proves coolant escaped somewhere, not which part failed. Record temperature behavior: slow warm-up points toward a thermostat stuck open, rapid overheat can involve a closed thermostat, low coolant, air, fan control or combustion leakage.

If the engine has been severely overheated, test for combustion gas, cylinder sealing and oil/coolant contamination before authorizing only a pump and thermostat. Save thermostat circuit codes and live temperature data. The code-to-test diagnostic workflow prevents an open-circuit code from being treated as automatic proof that the entire cooling complaint is mechanical.

Parts, tools, and consumables to stage

Stage the complete job before access is opened. Part numbers, seals, bolt-reuse rules and fluid specifications must be matched to the VIN, engine or chassis code; a familiar model name is not precise enough.

Parts and consumables	Tools and support equipment
• VIN-correct water pump and thermostat • Thermostat seal and three coolant-crossover O-rings • Small under-supercharger coolant pipe and seals as required • Fresh intake-manifold/supercharger seals • Approved engine coolant • Supercharger and accessory belts if worn, cracked or contaminated • Bumper/service-position hardware identified as single-use	• T25/T30, 5 mm Allen and M10 triple-square sockets • 8, 10, 13 and 16 mm sockets plus 16 mm wrench • Wobble extensions and low-range torque wrench • Hose picks, clamp pliers and vacuum caps • Cooling-system pressure tester or vacuum-fill tool • Drain pan, fender protection and labeled port plugs • Scan tool for thermostat circuit, pump/temperature and mixture data

Preparation and safety boundary

Work fully cold, disconnect the battery after data capture and support the front of the car at approved points. Never open the hot expansion tank. The bumper carries fog-light wiring, headlight-washer plumbing and painted surfaces; release and label each connection before the cover is moved away.

The supercharger is heavy enough to damage intake faces or fingers. Use its lifting eyes, keep the unit level and have a second person if control is uncertain. Plug every open intake port immediately. Count plugs before installation and after removal; one forgotten plug can destroy the engine.

Remove the access layers without losing the map

Remove the undertray, five lower T30 bumper fasteners, the T25/clip hardware at both wheel wells, hidden 10 mm corner fasteners, radiator shroud and fasteners beside the headlights. Release each bumper corner, disconnect fog lights and washer plumbing, and store the cover safely.

Drain coolant. Disconnect the bleeder line and headlights, remove the bumper-beam and behind-headlight fasteners, then move the front carrier to the approved service position with proper supports. Do not let the carrier hang on A/C lines or wiring.

Use separate trays for each access layer, label connectors by destination and photograph every hidden hose before it moves. Mark fastener length and location on a drawn component outline. Reassembly should follow a map created during removal, not memory or wire reach.

Exact repair sequence

Complete the following sequence in order. A bold lead identifies the action; the remaining sentence states the checkpoint that must be true before the next action begins.

1. Remove both drive belts. Record routing before releasing the supercharger and accessory tensioners. Inspect every idler and tensioner for noise, play or roughness while unloaded.
2. Clear the supercharger top. Remove the intake tube, airbox, both MAP connectors and the plastic covers. Label vacuum and electrical connections that cross the rear of the charger.
3. Disconnect charger coolant hoses. Catch residual coolant and cap the lines. Remove the front coolant-line bracket without bending the rigid pipe.
4. Remove six supercharger nuts. Lift the charger with its four eyes, keep it level and check that no rear connector or hose remains attached. Plug all exposed intake ports immediately.
5. Release the accessory belt and idler clearance. Use the 16 mm tensioner tool and loosen the M10 idler only enough to remove the belt if the configuration requires it.
6. Remove the pump pulley. Hold it by the approved method, remove its bolts and store them separately from plastic-housing fasteners.
7. Move the coolant crossover. Release the secondary-air hose, four T30 head fasteners and the T25 support by the pump. Pull the pipe straight from its O-rings rather than levering the plastic thermostat neck.
8. Replace the thermostat. Remove its seven T30 fasteners, pull the housing squarely and clean away from the engine opening. Install the new sealed housing and tighten evenly to 9 Nm on the documented configuration.
9. Renew all three crossover O-rings. Lubricate only with the approved coolant or service lubricant, insert the pipe squarely and torque the documented T30 fasteners to 9 Nm.
10. Replace the water pump. Disconnect the B8.5 vacuum nipple where fitted, remove seven T30 fasteners and release the pump. Clean outward, lubricate the new O-ring with coolant, hand-start all bolts and torque evenly to 9 Nm.
11. Restore pulley and accessory drive. Install the belt before final pulley torque so the pulley can be held by the prescribed method. Documented pulley bolts are 20 Nm and disturbed idlers 40 Nm; verify the exact hardware.
12. Replace the small coolant pipe under the charger. Remove old intake seals, clean the seal lands without dropping debris and install new seals in every exposed runner.
13. Lower the supercharger squarely. Confirm the small pipe and all intake seals engage, no rear harness is trapped, and all six nuts start by hand. Torque to 22 Nm in a criss-cross pattern on the documented configuration.

Reassembly and torque control

Reconnect the supercharger coolant lines, MAP sensors, vacuum lines, intake and both belts. Verify every rib sits in every pulley groove. Push the carrier back only far enough to establish a sealed, operable cooling system; leave bumper trim off until the hot leak test passes.

Use the cold pressure-test workflow before starting. Inspect the pump seam, thermostat perimeter, crossover ends, small charger pipe and every hose disturbed in service position. A dry test now can save another bumper removal.

Fastener or setting	Documented value	Applicability gate
Thermostat fasteners	9 Nm	Documented 3.0T configuration
Coolant-crossover T30 fasteners	9 Nm	Fit three new O-rings
Water-pump fasteners	9 Nm	Even passes on plastic/aluminum interfaces
Water-pump pulley	20 Nm	Use approved holding method
Accessory idler if disturbed	40 Nm	Verify exact idler and bolt
Supercharger nuts	22 Nm	Criss-cross pattern; fresh intake seals

Fluids, adaptations, and first start

Refill with the approved coolant by the current vacuum-fill or manual bleed procedure. Open the supercharger-circuit bleeders only as specified and capture displaced coolant. Start at idle, maintain reservoir level and close bleeders when an air-free stream appears. Keep hands clear of both exposed belt drives.

Monitor coolant temperature, cabin heat and fan command. Shut down for a rapid temperature rise, no cabin heat, pump noise or falling reservoir with no visible purge. After the system is stable and dry, reconnect headlights and bleeder line, restore the carrier fasteners, bumper, wheel-liner hardware and undertray.

Prove the repair under the original condition

Scan the engine for thermostat circuit and temperature plausibility faults. Pressure-test again after complete cooldown. Inspect beneath the supercharger with a mirror; a leak at the small pipe or crossover can hide in the valley before reaching the floor.

Road-test from cold through normal operating temperature without hard boost, then repeat under moderate load only after temperature is stable. Recheck both coolant circuits and levels next morning. Completion means no leak, no trapped-air behavior, correct warm-up and no new intake or MAP fault.

Common ways this repair goes wrong

• Replacing both parts without screening for overheating damage
• Letting the front carrier hang from hoses or wiring
• Leaving an intake port unplugged—or leaving a plug inside
• Crushing a rear harness beneath the supercharger
• Reusing flattened crossover or intake seals
• Completing the bumper before the first cold and hot pressure checks

A repair is not improved by clearing a code, adding sealant, tightening beyond specification or skipping a blocked step. When a checkpoint fails, return to the last verified state and correct the cause before more parts are installed.

Exact repair checklist

• VIN, engine/chassis code and installed component revision match the planned procedure.
• The failed component or interface was proven before disassembly; the before-state is saved.
• All seals, fluids, required new hardware and special tools are present before access is opened.
• Connectors, hoses, fastener lengths, routing and timing/alignment references are photographed and labeled.
• Open fuel, oil, coolant, intake or refrigerant interfaces are protected and every plug is counted.
• Replacement parts seat without force; every structural or sealing fastener starts by hand.
• Final torque, angle, sequence and ride-height/temperature conditions match current service data.
• All fluids, bleed routines, adaptations or calibrations required by the exact vehicle are complete.
• First start passes the listed stop rules; the repaired area is checked before trim or shields hide it.
• The original symptom is repeated hot and cold, the final scan is saved and the next-morning recheck passes.

Minimum record to retain

Retain the VIN, engine or chassis code, before-scan, symptom conditions, disassembly photos, connector labels, fastener map, service-data revision and every measured value. Record the exact fluid specification and quantity added, all adaptations or bleed routines completed, the first-start observations and a cold recheck. A later technician should be able to tell what was directly observed, what was replaced and which same-condition test proved the repair without relying on the invoice description.

• The documented repair uses front service position and removes the supercharger.
• Pump, thermostat and T30 crossover fasteners are 9 Nm on the documented configuration.
• Supercharger nuts are 22 Nm in a criss-cross pattern on the documented configuration.
• Both engine and supercharger cooling paths require air control and recheck.

This workflow is marked completed only when its stated repair and post-repair checks are represented. It does not certify an unseen vehicle, replace current service information or convert a different engine/chassis variant into the documented configuration.