Jeep Grand Cherokee: 3.6L Pentastar PCV Failure and Oil Consumption

The 3.6L Pentastar V6 uses a positive crankcase ventilation system that routes blow-by gases back through the intake manifold. The PCV orifice and oil-vapour separator membrane are prone to clogging with varnish deposits, especially on vehicles used for frequent short trips where the engine never fully reaches operating temperature. A blocked PCV raises crankcase pressure above atmospheric, forcing oil past valve stem seals and piston rings into the combustion chamber. Because the engine uses direct injection, recirculated oil vapour also coats the intake valves — which receive no fuel wash — causing progressive carbon buildup that reduces airflow and causes misfires. Oil consumption of 0.5 to 1.5 litres per 1,000 km can occur without any visible external leaks.

• Oil consumption of 0.5 to 1.5 litres per 1,000 km with no external leak visible
• Blue-grey smoke from exhaust on cold start or during hard acceleration
• Oil-fouled spark plugs found during routine inspection
• Rough idle or misfire codes caused by carbon-loaded intake valves
• Oily residue coating the inside of the PCV hose between cam cover and intake

1. 1

   Check the oil level against the last service record to estimate consumption rate.

2. 2

   Inspect the PCV hose from the cam cover breather to the intake manifold for internal oil coating.

3. 3

   Ask the seller how often they top up oil between services and request evidence of spark plug condition at the last service.

4. 4

   Remove the oil filler cap and inspect inside the cam cover for heavy sludge using a torch.

Parts involved: PCV / oil separator.

$450 to $3,800 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “How often do you need to top up the engine oil between services?”
• “Has the PCV valve or cam cover separator ever been replaced?”
• “Has the vehicle ever had a formal engine oil consumption test performed?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.