Ford Transit MK7, MK8 & Custom 2.2 TDCi Coolant Thermostat Housing Leaks & Overheating: Sensor Faults, Bleeding & OEM 1731770 (BK2Q-8594-AA) Guide

1. Why the 2.2 TDCi Duratorq Thermostat Housing (1731770) Warps, Cracks & Sticks Open

Fitted across Ford Transit MK7, MK8, Transit Custom V362, Tourneo Custom, as well as PSA/Fiat shared commercial platforms (Peugeot Boxer, Citroën Relay, and Land Rover Defender 2.2 TD4), the Puma 2.2-litre diesel engine uses a multi-port polyamide (PA66-GF30) water outlet housing bolted directly to the cylinder head above the transmission bellhousing.

Over 70,000+ miles of courier stop-start heat cycles, three distinct mechanical failures occur inside OEM 1731770 (Engineering Code: BK2Q-8594-AA):

• Flange Warpage & O-Ring Compression Set: The square-section rubber perimeter gasket flattens out while the plastic bolt ears bow slightly under thermal stress. Coolant weeps silently when the system cools overnight (cold-shrink leak), leaving crusty pink/orange crystalline deposits on top of the gearbox and starter motor solenoid.
• 88°C Wax-Pellet Thermostat Jamming Open: When the internal brass wax capsule fatigues, the main radiator valve stays partially open from cold start. On a frosty UK motorway run, engine coolant temperature never climbs above 62°C—leaving the driver with a freezing cabin, elevated fuel consumption, and aborted DPF regenerations (see our Ford Transit 2.2 TDCi DPF Vaporiser P244C / P2463 Guide—a stuck-open thermostat is the #1 hidden reason a new DPF vaporiser still won't regenerate!).
• 2-Pin NTC Temperature Sensor Brass Probe Corrosion: Coolant seeping past the internal brass thermistor seal corrodes the 2-pin electrical connector, sending erratic resistance spikes to the PCM.

2. Diagnostic Symptoms & Ford PCM Fault Codes (P0128, P0116, P0117, P0118)

3. OEM Cross-Reference & Engine Code Fitment Table (Ford, Peugeot, Citroën & VAG)

4. Shop Direct-Fit Thermostat Housings & Coolant Components (Birmingham UK Stock)

#1 BESTSELLER • SKU: BD1143

Ford Transit MK7 MK8 & Custom 2.2 TDCi 88°C Thermostat Housing + Sensor (1731770)

Complete water outlet flange assembly with pre-fitted 88°C thermostat, 2-pin ECT sensor & FKM gasket.

£23.61 View Part →

SKU: EN1006 • OEM 9827379280

Thermostat Housing Assembly for Peugeot Citroën Vauxhall & Fiat 2.0 / 2.2

Heavy-duty multi-outlet coolant thermostat housing for PSA/Stellantis 2.0 & 2.2 commercial diesels.

£80.70 View Part →

SKU: FR1018 • OEM 059115389K

Audi A4 A5 A6 Q5 Q7 & Touareg 3.0 TDI V6 Oil Filter Housing with Thermostat

Solves the notorious V-valley coolant & oil leak on 3.0 TDI V6 engines—includes integrated thermostat & seals.

£50.30 View Part →

SKU: XM1007 • OEM 13251441

Vauxhall Astra J 1.7 CDTi Radiator Coolant Outlet & Overflow Return Hose

Direct replacement for the brittle plastic degas return line between the thermostat outlet and header tank.

£28.31 View Part →

5. Step-by-Step Replacement & The Exact Ford Transit 2.2 TDCi Bleeding Procedure

Tools Required: Hose clamp pliers (for constant-tension spring clips), 8mm & 10mm 1/4-inch drive sockets with wobble extension, calibrated torque wrench (5–25 Nm range), fine Scotch-Brite pad, and 5 litres of Ford WSS-M97B44-D (Pink/Orange OAT) antifreeze mixed 50:50 with deionised water.

1. Depressurise & Partially Drain the Cooling System: Ensure the engine is cold. Slowly release the expansion bottle cap, then drain approximately 3.5 litres of coolant from the bottom radiator drain plug into a clean catch pan so the level drops below the cylinder head flange.
2. Create Access on the Nearside (UK Passenger Side) of the Head: Remove the intake resonator pipe above the gearbox. Protect the starter motor and alternator plug below with an absorbent workshop pad so residual coolant from the head jacket doesn't soak the starter solenoid terminals.
3. Disconnect Electrical & Coolant Lines: Unplug the 2-pin grey ECT sensor harness connector. Using spring-clip pliers, slide back the constant-tension clamps on the top radiator hose, heater matrix feed, and degas bypass spigot, then twist the hoses gently to break their seal before pulling them off.
4. Unbolt Old Housing & Prep the Cylinder Head Face: Undo the mounting bolts holding 1731770 to the cylinder head. Clean any white aluminium oxidation off the cylinder head mating face using a Scotch-Brite pad soaked in brake cleaner until smooth to the fingernail.
5. Bolt On the New BuyDay BD1143 Housing to 10 Nm: Verify the new moulded elastomer gasket is seated squarely in its groove (no liquid RTV needed!). Thread all bolts in by hand first, then tighten in a diagonal criss-cross sequence to exactly 10 Nm (88 in-lbs). Refit all hoses with their spring clips positioned right over the original rubber witness marks.
6. The Master Mechanic Airlock Bleeding Procedure (Do Not Skip!): Ford Transits are notorious for trapping an air pocket in the EGR cooler and high-mounted cab heater matrix. Fill the expansion tank to 15mm above the MAX line using a spill-free elevated funnel. Set the cab heater temperature dial to HI and blower fan to Speed 1. Start the engine and hold engine speed at 2,200–2,500 RPM for 4 minutes in bursts until the thermostat opens at 88°C (you will feel the top radiator hose turn piping hot and see air bubbles purge through the small top degas return hose). Let the engine cool, top up to the MAX mark, and refit the pressure cap.

6. Frequently Asked Questions (Ford Transit 2.2 TDCi Thermostat Housing 1731770)