# Head Gasket Failure and Oil Contamination — What Happens to Your Engine

> A failed head gasket is the most common cause of coolant in oil in New Zealand. This guide explains what happens, the warning signs, and how to respond.

- Canonical URL: https://www.eek.nz/news/head-gasket-failure-oil-contamination-nz
- Published: 2026-04-19
- Author: EEK Mechanical
- Publisher: EEK Mechanical, a trade name of Forman Pacific, LLC

## Why Head Gaskets Fail

The head gasket is one of the most stressed components in an engine. It must seal simultaneously against combustion pressure (up to 70 bar in a diesel), coolant pressure, and oil pressure. When the gasket fails — through overheating, age, or manufacturing defect — it allows these fluids to cross-contaminate. A failure between a coolant passage and an oil gallery sends coolant directly into the oil system.

## The Overheating Connection

Overheating is the primary cause of head gasket failure in New Zealand. A single severe overheating event — running the engine dry of coolant, a thermostat stuck closed, or a blocked radiator — can warp the cylinder head enough to compromise the gasket seal. Many drivers unknowingly cause a head gasket failure during an overheating event and then find milky oil days later when the damage becomes apparent.

## Warning Signs of a Head Gasket Failure

Watch for: milky oil on the dipstick or oil filler cap; white or grey exhaust smoke with a sweet smell; coolant level dropping without visible external leak; engine overheating more readily than normal; bubbles in the coolant reservoir when the engine is running. Any of these signs warrants immediate investigation — running the engine with contaminated oil accelerates bearing damage rapidly.

## What EEK Mechanical Does

We manufacturer-spec fuel system recovery the contaminated oil, provide a written contamination report for your insurer or workshop, and advise on the mechanical repair required. The head gasket replacement itself is carried out by your workshop — we handle the oil system decontamination and documentation that supports the claim or repair authorisation.

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Source: https://www.eek.nz/news/head-gasket-failure-oil-contamination-nz