Why an Old Subaru Impreza’s Head Gasket Might Blow
Your Subaru Impreza might experience issues with its head gasket, especially if it's an older model. Several factors come into play, including the composition of the coolant, the design of the engine, and the materials used in the gaskets and bolts. In this article, we explore why an old Subaru Impreza’s head gasket might blow, focusing on key areas and providing detailed insights.
Factors Contributing to a Blown Head Gasket
1. Old Engine Oil and Water-Based Coolant
The use of old engine oil and water-based coolant can be detrimental to your Subaru's head gasket. Traditionally, older models were designed to use oil-based coolant, but if you've been using water-based coolant, it may cause issues. Water-based coolant contains chemicals that can strip the walls of the engine, creating a build-up of metal in your pipes. Additionally, if the head gasket is not an MLS (Multi-Layer Steel) gasket, it may be coated with graphite, which disintegrates over time when exposed to debris in old engine oil.
Design Hazards and Engine Efficiency
2. Open Deck Engine Design and Head Gasket Design
Subaru's engine design can contribute to head gasket issues. The open deck design of the engine block lacks structural integrity, which can lead to instability in the cylinder bore. Furthermore, horizontally opposed engines, like the Subaru boxer engine, have uneven coolant circulation. The side with the water pump receives better coolant circulation than the other side, leading to inconsistencies in heat distribution and pressure.
Specific Engine Models and Head Gasket Issues
3. Older WRX vs. Bored Out 2.5 Liter Models
Subaru engines have experienced head gasket issues for years, with the cause being multifaceted. The early WRX models with a closed deck engine had fewer issues compared to the later stronger, bored-out 2.5-liter variants. This was due to the use of MLS head gaskets and longer, larger head bolts designed to enhance long-term durability. However, the boxer engine design means that the head gaskets are constantly exposed to oil, unlike in most other engine types where the gaskets are on top of the engine and not bathed in oil.
Over Time, Gaskets Can Leak
4. Exposure to Oil and Material Degradation
As the engine ages, the head gaskets, which are located on the side of the boxer engine, become constantly exposed to oil. This prolonged exposure can lead to degradation and eventual failure. Even if the engine doesn't have design flaws, the constant bath in oil can weaken the gaskets over time. This is unlike other engine designs where the gaskets are protected from oil exposure.
Conclusion
Understanding the potential reasons behind a blown head gasket in your old Subaru Impreza is crucial for maintenance and troubleshooting. Keep an eye on the coolant, use the appropriate type, and consider the design of your engine. Regular checks and timely maintenance can help prevent significant issues and keep your vehicle running smoothly.