2005-2008 Acura RL Cylinder Head: Overheating, Diagnosis, and Replacement Guide

Part Identification: Front vs. Rear Cylinder Heads

The 2005-2008 Acura RL uses a 3.5L V6 engine (code: J35A8) that has two separate, non-interchangeable cylinder heads. It is critical to order the correct head for the bank you are servicing.

• Front Cylinder Head (Bank 2): This head is located on the side of the engine closest to the radiator. The primary OEM part number for the complete assembly is 10004-RJA-A00.
• Rear Cylinder Head (Bank 1): This head is on the side of the engine closest to the firewall. The OEM part number for the complete assembly depends on the model year: 10005-RJA-A00 for 2005 models and 10005-RJA-A01 for 2006-2008 models. Note that the rear head assembly is often listed as discontinued from OEM suppliers, making used parts a common necessity.

Symptoms of a Failing Cylinder Head

Cylinder head issues on the Acura RL almost always stem from a blown head gasket caused by engine overheating. The symptoms of a cracked or warped cylinder head are nearly identical to those of a failed head gasket. If you are replacing a head gasket, the cylinder head must be inspected by a machine shop.

• Engine Overheating: This is the most common and critical symptom. The temperature gauge may climb towards 'H', especially under load or after turning off the A/C. Driving while the engine is overheating can cause the aluminum heads to warp, which is a primary cause of failure.
• Unexplained Coolant Loss: You may find yourself repeatedly adding coolant, but see no visible leaks on the ground. This can happen if coolant is leaking internally into the combustion chamber or the engine oil.
• White Smoke from Exhaust: Sweet-smelling white smoke from the tailpipe, especially on startup, is a classic sign that coolant is being burned in the cylinders.
• Bubbling in Coolant Reservoir: Combustion gases being forced into the cooling system can cause the coolant to bubble or even appear to boil in the overflow tank, sometimes forcing coolant out.
• Milky or 'Chocolate Milk' Engine Oil: This indicates that coolant is mixing with the engine oil due to an internal crack or failed head gasket. You can check for this on the oil dipstick or under the oil filler cap.
• Engine Misfires & Rough Running: Coolant leaking into a cylinder can foul the spark plug, leading to a rough idle, poor acceleration, and a flashing Check Engine Light, often with codes like P0300 (Random Misfire) or P0301-P0306 (Cylinder-specific misfires).

Known Issues, Recalls, and Technical Service Bulletins (TSBs)

A Major Advantage: No VCM System

Unlike many other Honda and Acura models with J-series V6 engines, the J35A8 used in the 2005-2008 RL does not have Variable Cylinder Management (VCM). This is a significant reliability advantage. VCM systems are known to cause issues like increased oil consumption, fouled spark plugs, and premature piston ring wear. Buyers can be confident that this specific engine is not prone to those particular VCM-related failures.

Technical Service Bulletin: Ticking Noise from Cylinder Head

A TSB was issued for a ticking or knocking noise at idle, which becomes more noticeable as the engine warms up. This noise can be caused by excessive clearance in the rocker shaft bridge. The fix involves a specific procedure of loosening and re-torquing the rocker shaft bridge bolts to crush the bridge properly around the rocker shaft. The final torque value is 18 ft-lbs, following a specific sequence for the front and rear heads.

Safety Recall: Power Steering Hose Leak

NHTSA issued recall 07V551000 for 2005-2008 Acura RL models. The power steering fluid feed hose can deteriorate from high under-hood temperatures, leading to cracks and fluid leaks. If power steering fluid leaks onto the hot catalytic converter, it can generate smoke and potentially cause an engine fire. Owners should ensure this recall has been performed on their vehicle.

Buying a Used Cylinder Head: What to Check

Given the high cost and potential scarcity of new OEM heads, a quality used cylinder head is an excellent value. However, never install a used cylinder head without having it professionally inspected and prepared by an automotive machine shop. The cost of this service is minor compared to the cost of re-doing the entire job.

1. Verify Compatibility: Double-check that you have the correct head (Front or Rear) for your specific year. The casting number 'RJA' should be visible on the exhaust side of the head.
2. Initial Visual Inspection: Before taking it to a shop, look for obvious deal-breakers. Check for visible cracks, especially around the spark plug holes and between the valve seats. Inspect the camshaft bearing journals for deep scoring or gouges. Ensure all threaded holes are intact.
3. Mandatory Machine Shop Services:
   • Pressure Testing: The shop will seal the head's coolant passages and pressurize them to check for microscopic cracks that are invisible to the naked eye. A head that fails a pressure test is junk.
   • Check for Warpage: The shop will use a precision straight edge to measure the flatness of the head deck. An overheated engine can easily warp an aluminum head.
   • Resurfacing (Milling): If the head is warped within allowable limits, the machine shop will mill a tiny layer of metal off the deck to make it perfectly flat. This is critical for ensuring the new head gasket seals properly.
4. Valves and Seals: While the head is at the shop, it is highly recommended to have them perform a valve job and install new valve stem seals. The labor is minimal at this stage and ensures proper valve sealing and prevents future oil consumption from worn seals.

Cost to Replace a 2005-2008 Acura RL Cylinder Head

Replacing a cylinder head is a labor-intensive job. If one head has failed due to overheating, it is often recommended to service both heads at the same time. The costs below are estimates for a single cylinder head.

Replacement Overview & Torque Specs

Cylinder head replacement is a difficult and complex job recommended only for experienced DIY mechanics or professionals. It requires partial disassembly of the engine, careful handling of the timing belt, and precise tightening procedures.

• Difficulty: 5 out of 5 (Expert)
• Estimated Time: 10-15 hours
• Special Tools: Precision torque wrench, angle gauge (if using TTY bolts), engine hoist or support bar.

Cylinder Head Bolt Torque Specifications (J35A8)

The J35A8 typically uses 6-point head bolts. Always apply fresh engine oil to the bolt threads and under the heads before installation. Tighten the bolts in the correct sequence (found in the factory service manual) using the following three-step method:

1. Step 1: Torque all bolts in sequence to 29 ft-lbs.
2. Step 2: Torque all bolts in sequence to 51 ft-lbs.
3. Step 3: Torque all bolts in sequence to 72.3 ft-lbs.

Frequently Asked Questions (FAQ)