SCCA RunOffs Indianapolis Motor Speedway Speedway, Indiana ©2017 Rupert Berrington

Engineering Tip #5: Miata Engine Oil Leaks Guide

Oil leaks are some of the most frustrating maintenance problems. Fortunately, they are often easy to repair or prevent.

Let’s face it, most Spec Miata or other Miata race car builds start as high mileage street cars that are not always maintained to a high standard. Unless you are planning to completely rebuild your engine, there are a few minor repairs to consider before taking your car on track.

Engine oil leaks are common on higher mileage engines and, if not repaired, can cause a real mess when it comes time to make repairs to your car. If you have changed out a clutch on an early Miata with a cam angle sensor “O” ring leak, you know what I mean!

In addition to oil leaks causing a mess to your car, they can damage the clutch, timing belt and wiring harnesses. First, try to determine where the leak is located. Front or rear of the engine? Is it on the higher side of the engine or down low at the oil pan? A leak on the front of the engine is typically easier to diagnose; a leak on the top of the engine could indicate valve cover or even the oil cap/PCV gasket. A leak from the lower portion of the engine could be cam or crank seal leakage (under timing belt covers). On 1.8L engines, check the oil cooler to engine gasket (located on intake side of engine block).

On the rear of the engine, oil leaks that begin on the top side of the engine can easily be misdiagnosed for a leaky rear main engine seal. Thoroughly clean all oil and dirt from the suspected leak area. Then run the engine and monitor areas to where the source of the leak may occur:

1990-2005 – Inspect valve cover gasket, PCV grommet and oil filler cap seal.
1990-2005 – Inspect timing belt cover area for cam and front main seal leaks.
1990-1997 – Inspect for leaky cam sensor O ring (very common!).
1999-2005 – Inspect cam seal plug.
1990-2005 – Inspect dipstick tube “O” ring. (often overlooked!)
1990-2005 – Inspect rear main seal
1990-2005 – Inspect  oil pan

Miata Oil Leaks