Honda Civic MK9 i-DTEC Leaking Oil Cooler Plate Replacement

The plate is mounted on the front-left of the engine behind the DPF, near the EGR cooler. When it leaks, oil is thrown across the cylinder head, the rear and underside of the block, the back of the front subframe and onto the undertray, spread further by the auxiliary belt and water backsplash. The symptom builds gradually: faint oily films appear on the ground, worsen in wet weather, then become established sludge and eventually steady oil loss (weekly top-ups by roughly 130,000 miles in this case). Inspect the oil pan too, but a wet area on the front side under the EGR cooler points to the plate rather than the sump.

Buy a new oil cooler plate assembly (15510-RZ0-G00); it comes with the oil-cooler-side O-rings and gaskets already fitted, so there is no need to order those separately. A genuine part may carry a "REV 3" stamp indicating a revised design. Add the water passage gasket (19415-RZ0-G01) and water pump gasket (19222-RZ0-G01). Since the belt and thermostat come off anyway, renew them too (belt 31110-RZ0-G02). Stock 4.7L of oil and about 6L of Honda Type 2 coolant. The manual also lists one-time-use parts worth renewing: the LP EGR cooler O-ring (18752-RZ0-G01), the heater pipe O-ring, the LP EGR passage gasket, DPF self-locking nuts, and turbo gaskets with a fresh oil feed bolt washer. Purchase an hour of access to Honda's Maris technical portal (around 10 euros) and download the relevant PDFs before starting.

The MK9 offers no front jacking point besides the sills. Lift at the front tow hook with a trolley jack, a widely used spot, accepting a little flex in the soft chassis. Set an axle stand under each front sill with a folded cloth protecting the pinch weld. Remove both front wheels and take off the complete front undertray to open up the underside of the engine.

Warm the engine first so the oil drains freely, then release it at the sump plug and remove the filter. Allow the engine to cool before dealing with coolant. Set the cabin heater to maximum to open the heater valve, then drain coolant by removing the expansion tank cap and opening the small drain tap at the base of the radiator, which sits just above the subframe. Open the cooling-system bleed valve at this stage to prepare for the refill.

Disconnect the battery, as the alternator is coming out. Undo the two bolts on the coolant expansion tank, release the hose clamps with pliers and ease the hoses off; lifting the tank clear of its mounts first makes this easier. Loosen the tank's engine-bay brackets to free up working space.

Optional but well worth it: taking off the left-side engine mount greatly eases access to several water pump and alternator fasteners. It needs a socket deep enough to reach the bolt below the mount tower; without one the job can still be done, just with more effort. Do this before tackling the alternator.

These engines use a hydraulic belt tensioner. Operate it slowly, taking at least three seconds to move it through its full travel, and never let it spring back, as that can break it. Release tension with a long, ideally straight 18mm spanner and slip the belt off by hand or with a trim tool; alternatively, work from below with two wrenches linked together and pulled toward you, using a glove or cloth to protect your hand. Unplug the alternator connectors and harness clamps, then remove its two bolts. The upper bolt is awkward unless the engine mount is out; the lower bolt is long and runs through the alternator into a bracket on the water passage, and may need a few hammer taps to free and to realign on refitting. On refitting, tighten the upper alternator bolt to 12 N·m; the longer lower bolt takes 45 N·m.

Unplug the air-fuel (A/F) sensor and unscrew it with the 24mm slotted oxygen-sensor socket. Unplug the EGT sensor, free its wire from the clip and undo it; torqued to 61 N·m, it will be tight. Take off the heat cover (three bolts and one nut). Detach the pressure sensor hose by releasing its clip and gently rocking it off; the roughly ten-year-old hoses can be brittle, so a cloth between pliers and hose helps avoid tears. Loosen the EGR pipe at top and bottom, remove the DPF bolts, nuts and brackets (the body- and engine-side mounts can just be loosened and left in place), then withdraw the EGR pipe. Detach the DPF where it joins the turbo, then lift the entire assembly clear; its own cover need not be removed. Torque figures for reassembly: bring the A/F sensor up to 44 N·m and the EGT sensor to 61 N·m; the DPF-to-turbo joint and the DPF brackets each take 45 N·m (run the brackets up in two to three sequential passes), and the DPF cover is set to 12 N·m. Use fresh self-locking nuts where the DPF bolts up during reassembly.

Release the oil return hose at its clamp from the turbo side, which is easier to reach than the pipe side, then remove the outlet hose. Detach the vacuum line at the top and unplug the wastegate connector. Separate the turbo from its bracket, leaving the bracket on the engine. Free the oil bypass pipe from its engine mounting and lift the turbo out as one unit with the pipe still attached. Torque on reassembly as follows: the turbo-to-manifold studs to 78 N·m, the turbo bracket to 45 N·m, the oil feed bolt to 40 N·m over a new washer, and finally the oil bypass pipe to 12 N·m using a new gasket. Use new turbo gaskets on reassembly.

Free the air box cover from its housing so it can be pulled aside; it only needs to be loose. Disconnect the intake pressure control valve hose, then remove the valve itself, which is secured by two bolts and two nuts with an electrical connector on its underside.

Disconnect the EGR differential pressure hose and unbolt the pressure sensor, setting it aside. Remove the nut and two bolts on the EGR side, then release the hose clamp on the turbo side to free the airflow joint.

With the DPF, turbo and EGR plumbing clear, release the heater pipe where it meets the water passage; it is held by one bolt on the engine beneath the turbo and a second on the passage itself. Continue freeing the remaining EGR connections and remove the water passage to expose the oil cooler plate, the part that actually leaks. Remove the old plate and scrape any bonded gasket remnants from the sealing faces with a razor or scraper until they are clean and flat.

Install the replacement oil cooler plate (15510-RZ0-G00) with its pre-fitted O-rings and gaskets, and fit the new water passage gasket (19415-RZ0-G01) and water pump gasket (19222-RZ0-G01). Lightly oil O-rings and handle any shims with care. Rebuild every removed assembly in reverse order, applying the torque figures given in the earlier steps and using new gaskets, self-locking nuts and the oil feed bolt washer where specified.

Refit the undertray and wheels and lower the car. Add 4.7L of fresh oil with a new filter and about 6L of Honda Type 2 coolant, using the bleed valve to purge trapped air. Reconnect the battery, run the engine, and inspect the repaired area for leaks. Recheck oil and coolant levels once everything has settled and been topped up as needed.