HEAD GASKET REPAIR OR REPLACE

The head gasket forms a seal between the Subaru engine block and cylinder head. It is the most critical gasket in the engine and the most difficult to diagnose. It seals both the combustion chambers and the coolant passages in a Subaru engine. The Subaru head gasket has to cope with high internal temperatures and combustion gases under high pressure. Due to the extreme range of hot and cold temperatures and pressures on a large surface it is common for head gaskets to leak between chambers over time. These leaks not externally visible. You may see bubbles in the overflow reservoir, or sludgy residue on the walls of the overflow reservoir, or random engine overheating. When a head gasket fails it can either leak engine oil to coolant or coolant to the compression chamber. Either of these may cause engine damage and significant operational problems like burning oil and overheating, which may show up as white exhaust smoke. Occasionally, there will be a compression leak in the gasket, which will have to be replaced, before severe damage occurs. If the gasket fails in this way, a variety of problems can occur, from compression loss (leading to power reduction, or a rough running engine), to exhaust gases being forced into the cooling system, leading to the engine overheating and increased engine wear due to the motor oil being mixed with coolant. Over the years we have not seen many non-turbo models with internal head gasket issues, while we have replaced many turbo WRX, STI, Liberty RS ¬¬, Forester GT/XT head gaskets, and if in the advanced stages, provided exchange engines. However, we have also seen an increase of liberty/Outback H6 EZ engines with internal defective gaskets at about 150 to 200 000km.

Engines EJ 205, 207, 255, and 257 DOHC 4-cylinder turbo from 1991-current, causes and options

Internal head gasket leaks in turbo models are usually caused by problems with one or more of the peripheral components, such as excessive turbo boost, failure of cooling fans, defective wiring, radiator leaks and blocked radiator cores. A blown head gasket in a turbo model usually indicates a replacement engine. There are two reasons for this: one, the OEM pistons consume excessive oil, meaning that replacing the head gasket using the original pistons increases the risk of a future engine failure and two, it is common when a head gasket goes on a turbo model for bearings, crankshafts and other components to be damaged.

Visible leaks and false fixes

These leaks result in coolant and engine oil seeping out past the head gasket and running down the cylinder head, where they are usually visible under careful inspection. They can't be fixed by simply re-torqueing the head. They are sometimes hard to spot, showing only as slight staining where the head bolts onto the block. EJ25 and most EZ30 Subaru non-turbo engines are prone to this type of leak, which will often go undetected for some time as it is only in the advanced stages that coolant loss causes overheating. Customers who are attuned to their Subarus may report unusual smells, caused by coolant residue burning on exhaust pipes, and hot components; however most customers will be unaware of the problem. Additives such as cooling system conditioners, Bars Stop Leak, WWP-99, and Wynn's Stop Leak should never be used as these can compromise the cooling system, causing overheating and serious damage to engine components. The only practicable solution is a proper Subaru head gasket repair, which is one hundred percent effective when done correctly.

Engines EJ251,252,253, SOHC 4-cylinder non-turbo from 1999 to current, Liberty, Forester, Outback, Impreza

In virtually all cases of head gasket failure in non-turbo 4-cylinder engines the cause is the design of the single layer OEM head gasket. If the problem is repaired using another OEM single layer gasket then the same issue will inevitably arise again. The mileage of the vehicle at the time of failure should determine the course of action. If the engine has travelled less than 120,000 kilometres it makes sense to replace the head gasket. At the same time, we advise performing a major service as this will mean a considerable saving in labour costs. If the engine has travelled 150,000 or more, consideration should be given to replacing the engine with a rebuilt or remanufactured engine from Subaru Engines Australia. External head gasket leak problems are rarely reported in turbo models, which are all fitted with the more robust multi-layer gasket.

Engines EZ30 DOHC 6-cylinder (H6) from 2001 to current

While these models are not as prone to the same problems as the 4-cylinder models, they have their own unique vulnerability, with the heater core. Unlike other models the EZ30 heater does not have a separate tap, and runs in series with the engine cooling system, meaning if the heater core becomes blocked, circulation of coolant is impeded throughout the system and the engine will overheat. The only early warning sign drivers might notice is an intermittent gurgling sound from behind the dashboard. If the heater core is replaced at this stage no further repairs should be required. However, if the early signs are overlooked, the engine will begin within two years to repeatedly overheat and the head gasket will fail, possibly damaging other components such as bearings, rods and crankshafts. The heater cores in these models commonly begin to fail around the 120K kilometre mark.