by Jim Kerr
One of the most frustrating vehicle ownership experiences is when your vehicle marks its territory on your driveway or garage floor with a puddle of oil or antifreeze. Even small leaks can cause damage if not repaired, so why can’t the manufacturers develop leak proof engines and transmissions? Compared to vehicles even 10 years old, new vehicles are sealed much better. New seal materials and technology have helped considerably, but the working environment still has a large impact on the effectiveness of seals and gaskets.
There are five things requiring sealing on an engine: oil, coolant, fuel, compression, and dirt. Yes dirt – some things need seals to keep them out, not in. Two kinds of materials are used to contain these fluids – seals and gaskets.
Rotating shafts, such as crankshafts or belt-driven camshafts use lip-type seals to hold the oil in. These are sometimes referred to as “dynamic seals” because the part is moving inside the stationary seal. Even small oil leaks past a camshaft seal can destroy rubber timing belts and cause the engine’s valves to be bent. This is one place not to scrimp on repairs!
Many seals will have two sealing lips – one to keep the oil in and another facing the opposite way to keep dust and dirt away from the oil seal side. When dirt gets into a seal, it embeds in the softer seal surface and then acts like a grindstone on the hard metal shaft turning inside the seal. A groove wears into the shaft and a leak starts. Some parts, for example – front crankshaft damper pulleys, can sometimes be repaired by installing a “speedy-sleeve”. This thin metal band is pressed over the worn groove so the seal has a new surface to ride on. It is also possible to build up worn surfaces by spray welding and then grinding them back to specifications, but this is expensive and only used for rare or high priced parts. Most automotive parts are relatively cheap, so worn ones are usually replaced.
Gaskets have changed a lot in the last few years. Some cheap aftermarket gasket sets still use cork. Cork relies on oil seeping into the gasket to make it swell and seal. Sealers should never be used when installing cork gaskets. Rubberized cork gaskets were a big improvement in sealing, but most new gaskets are made of synthetic rubber. RTV silicone has been used to make gaskets, but its use is decreasing. It must be installed on a clean, oil-free surface and this makes it difficult for some service applications.
The biggest problems with gaskets have been distorted gasket mating surfaces and over-tightened bolts. Stamped steel engine covers have mostly been replaced by moulded plastic or cast aluminium covers. These both offer more even clamping of the gasket and don’t distort as easily. Many new gaskets have internal metal spacers moulded into the material to prevent over-tightening the gasket.
Head gaskets and intake manifold gaskets have a very difficult job to do. Head gaskets seal engine compression, coolant, and sometimes oil. Intake gaskets need to seal air, fuel vapours, and coolant. Aluminum engine parts have made the sealing job even harder. Aluminum expands about .006inch for every inch of material, for every 28C change in temperature. An average cylinder head could expand nearly ½ inch in length from a cold winter start to full operating temperature. If the gaskets were attached solidly to the parts, they would be ripped apart by the expansion. Instead, the gaskets are made to allow the parts to slide on each other as temperatures change.
Many bolts used to hold critical engine parts together are now of the “torque to yield” type. This means the bolts stretch as they are tightened and remain in an elastic state to allow parts to move. Torque to yield bolts are designed to be used only once. After that their elastic ability is limited, so new bolts must be used each rebuild. Use the wrong bolts or torque and gaskets fail, causing head gasket compression leaks, warped heads, and coolant leaks.
Coolant leaks should be checked immediately. External leaks leave stains and puddles, but sometimes they can leak internally as well. Even a couple ounces of antifreeze mixed in the engine oil will start to destroy engine bearings.
There are thousands of types of sealers, gaskets, and seals. The key to maintaining a leak free engine is to use the correct product for the application, tighten it to specifications, and make sure everything is clean and straight before putting it together. With care, even older engines can remain as leak free as many new engines are.