Singapore Industrial Diesel Engine Passes a Cold Charge-Air Leak Check but Develops Underboost After Extended High-Load Operation as Heat-Dependent CAC End-Tank Cracking Is Investigated

The Cold Pressure Test Did Not Reproduce the Operating Fault

An industrial diesel engine in Singapore developed persistent underboost after extended high-load operation.

A cold charge-air pressure test showed little evidence of leakage.

Turbocharger control and major hoses also appeared acceptable.

Because the problem emerged only after the engine and charge-air cooler reached operating temperature, technicians investigated whether the CAC end tank or joint opened a leak only when hot.

Materials Change Dimension With Temperature

Charge-air coolers may use:

• aluminum cores;
• welded end tanks;
• crimped joints;
• seals;
• or mixed-material construction.

As temperature changes, these parts expand at different rates.

A small crack or marginal joint can behave as:

Cold component → Crack closed or nearly sealed

then

Hot component → Thermal expansion changes joint geometry → Leak opens

This explains why a cold workshop test may not reproduce the boost loss.

High Boost Added Pressure to the Thermal Effect

Extended engine load produced two conditions simultaneously:

1. higher component temperature;

2. higher charge-air pressure.

A marginal joint therefore experienced both thermal expansion and greater pressure stress.

Possible leak locations included:

• end-tank welds;
• crimp interfaces;
• mounting-stressed corners;
• tube-to-header joints;
• or previously repaired areas.

The Investigation Recreated the Correct State

Rather than relying solely on a cold leak test, technicians considered:

• leak behavior after warm-up;
• visible oil mist around joints;
• temperature-dependent pressure loss;
• end-tank distortion;
• mounting stress;
• and cooler expansion.

Any pressure testing needed to remain within the manufacturer’s approved limits.

Singapore’s Hot, Humid Continuous Operation Was Technically Relevant

Industrial engines can remain under load for long periods.

High ambient temperature can also reduce how quickly components shed heat.

This helped make a marginal thermally sensitive crack more repeatable than during a short cold inspection.

Why the Turbocharger Appeared Suspicious

The ECU requested boost, but manifold pressure remained low.

That often directs diagnosis toward the turbocharger.

However, a healthy compressor can generate the required air while the downstream system loses it through a crack that exists only when hot.

Technical Lesson

A leak test is only valid for the state in which it is performed.

When a complaint is temperature-dependent, technicians should ask whether the component geometry changes enough between cold and hot conditions to alter sealing.

FAQ

Can a charge-air cooler leak only when hot?

Yes. Thermal expansion can open a marginal crack or joint that seals when cold.

Does a cold pressure test rule out every boost leak?

No. Temperature-dependent leaks may require testing under representative operating conditions.