One of the most expensive misdiagnoses we see in UK workshops happens on the second-generation 3.0 TDI V6 (204 bhp / 245 bhp / 272 bhp). Oil and pink G13/G12evo coolant drip down the rear of the gearbox bellhousing, leading general garages to quote £1,400+ to pull the transmission for a 'rear main crankshaft seal'. In reality, the fluid is pooling inside the cylinder block V-valley from a warped composite Oil Filter Housing & Integrated Coolant Thermostat Assembly (OEM 059115389K / 059115389P) and draining out the rear valley weep hole!
1. Why the 3.0 TDI V6 V-Valley Floods with Oil & G13 Coolant
Nested deep inside the 90-degree V of the 3.0-litre V6 diesel block sits the combined oil filter module, water-cooled oil cooler plate, and coolant thermostat housing (OEM 059115389K). Subjected to extreme radiant heat from the adjacent turbocharger, the polyamide housing warps and its purple Viton figure-of-eight seals flatten out.
2. UK Workshop Diagnostic Fault Codes, Symptoms & Root Causes
| Fault Code / Defect | On-Road / MOT Symptom | Root Cause & Permanent Workshop Fix |
|---|---|---|
| P0128 / 16512 | Coolant Thermostat (Coolant Temp Below Regulating Temperature) | Integrated thermostat inside 059115389K sticking open; engine struggles to reach 90°C on UK motorway runs. |
| P164E00 | Oil Pressure Regulation Valve — Electrical/Mechanical Malfunction | Sludge or degraded gasket fragments restricting oil gallery passages in the filter housing base. |
| Visual MOT Defect 8.4.1 | Fluid Leaking Excessively Between Engine & Gearbox | V-valley overflow drain hole channelling leaked oil/coolant down the rear bellhousing. |
3. Verified OEM Part Number Cross-Reference & UK Fitment Guide
| OEM Reference | UK Vehicle Application | Component & Workshop Spec |
|---|---|---|
| FR1018 — 059115389K / 059115389P / 059115389H | Audi A4, A5, A6, A7, A8, Q5, Q7 & VW Touareg 3.0 TDI V6 (CDUD, CLAB, CDUC, CKVB, CJGD) | Complete Oil Filter Housing with Integrated Coolant Thermostat & Base Seals |
| BD1199 — 11428596283 | BMW 1, 2, 3, 4, 5 Series & X3/X4 2.0d (N47 / B47) | Complete Oil Filter Housing, Cooler & Gasket Assembly |
| BD1122 — 1829179 / BK2Q-6B624-CE | Ford Transit MK7/MK8 & Custom 2.2 TDCi FWD | Upgraded Modified Engine Oil Cooler & Filter Housing Assembly |
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4. Step-by-Step UK Workshop Fitting Procedure & Torque Specs
- Vacuum the V-Valley Dry Before Unbolting the Housing: Once the upper intake manifold is lifted off, use a vacuum extractor and blue roll to soak up all standing oil and coolant in the V—otherwise, lifting the old 059115389K housing will dump coolant straight into the open crankcase oil return ports!
- Clean the Aluminium Block Mating Deck: Wipe the machined aluminium valley floor with lint-free cloth and brake cleaner; never scrape the soft alloy with a metal chisel.
- Install the New BuyDay FR1018 (059115389K) Assembly: Verify the new elastomer seals are seated in the base channels, position the housing onto its dowel pins, and torque the T30 mounting bolts in a spiral pattern from the centre outward to exactly 9 Nm + 45 degrees (or 12 Nm final).
- Change the Engine Oil & Vacuum-Fill G12evo Coolant: Because tiny drops of coolant inevitably enter the oil gallery when the old housing is lifted, always drain the sump and refill with fresh VW 507.00 5W-30 oil before starting the engine.
5. Master Mechanic Q&A: UK Workshop & MOT Questions Answered
Q: Why is coolant leaking from the back of the gearbox on my Audi Q7 or A6 3.0 TDI?
Dave Mercer (Master Tech): The 3.0 TDI V6 engine block has a built-in drain channel at the back of the V-valley. When the oil filter and thermostat housing (059115389K) leaks inside the V, the fluid drains out the back of the block and runs down the transmission bellhousing.
Q: Does BuyDay part FR1018 (059115389K) include the thermostat and gasket?
Dave Mercer (Master Tech): Yes, FR1018 comes as a complete ready-to-bolt-on unit including the housing body, cap, integrated thermostat, and base Viton sealing gaskets.
📚 Related UK Workshop Diagnostic & Replacement Guides
- Ford Transit MK7, MK8 & Custom 2.2 TDCi Coolant Thermostat Housing Leaks & Overheating: Sensor Faults, Bleeding & OEM 1731770 (BK2Q-8594-AA) Guide
- BMW N47 & N57 2.0d/3.0d Crankcase Breather Pipe & Intercooler Boost Hose Failure: Oil Mist Leaks, Whistling & OEM Replacement Guide (13717803842 / 13718512014)
- Engine Oil in Coolant Expansion Tank? BMW N47/B47 (11428596283) & Ford Transit / Ranger 2.2 & 3.2 TDCi (1829179 / 1746665) Oil Cooler Guide
- UK Winter Car & Van Survival Guide: Cold Cabin Heating, Stuck Open Thermostats, Frozen Door Seals & Cold-Start Diesel Leaks
- VW Golf MK8, Audi A3, Seat Leon, Skoda Octavia & Cupra (2020–2025) Park Assist Fault: Ultrasonic Sensor 5WA919275B Guide
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