P0217 on Jaguar: How to Diagnose & Fix

The naturally aspirated and supercharged 4.2-litre AJ34 V8 in the X350/X358 carries an unusually large amount of load-bearing plastic in the cooling system. The thermostat housing is plastic and its internal support fractures, which lets coolant recirculate through the engine while bypassing the radiator — the car overheats even though the coolant level and the pump are fine, which sends people chasing head gaskets. Separately, the water pump uses a composite impeller that erodes and shreds, and the plastic retaining ring holding the pump's O-ring crumbles at the bottom of the pump. Additional chronic weep points are the overflow nipple on the coolant expansion tank and the two heater hoses that run beneath the intake manifold. This is a distinct problem from the X351's water pump failures — different engine family, different parts.

The mechanical water pump on the 5.0L AJ133 V8 is a recognized weak point. Coolant migrates past the shaft seal into the bearing housing, corroding the bearing so the impeller shaft is no longer properly supported. This accelerates wear on the flat-face mechanical seal and lets coolant escape at the pump. Failures are common and can occur early — some owners report leaks in under 20,000 miles. Left unaddressed it leads to progressive coolant loss and overheating risk on an aluminum V8.

The AJ-V8 routes coolant through molded plastic pipes in the engine 'valley'/V (the crossover pipe that plugs into the block, and on 4.2/supercharged cars the valley pipes beneath the supercharger). With age the plastic embrittles and the molded seam splits, or the stubs shear at the block, causing sudden major coolant loss. Because the failure is buried under the intake/supercharger, leaks are hard to spot and can strand the car. Jaguar published a TSB (JTB00566) on coolant leaks from the engine compartment.