Engine Repair and Performance Flashcards

A cooling system pressure test holds pressure, but coolant is still being lost and white exhaust smoke has a sweet smell. Which test best confirms a combustion leak into the coolant?

Answer: Block (combustion leak) chemical test

A chemical block tester detects combustion gases (CO2) in the coolant.

An engine overheats only at highway speed but stays normal in traffic. The most likely cause is:

Answer: Restricted radiator core

At speed, ram air should cool; a clogged radiator can't move enough heat under high load.

What does a thermostat stuck open typically cause?

Answer: Slow warm-up and poor heater output

Constant coolant flow to the radiator prevents the engine from reaching operating temperature.

A gradually decreasing vacuum reading as engine rpm is held at 2500 most likely indicates:

Answer: Restricted exhaust system

A clogged exhaust (e.g., converter) causes backpressure to build, steadily lowering vacuum.

Positive crankcase ventilation (PCV) valve stuck closed can cause:

Answer: Increased crankcase pressure and oil leaks

Blow-by gases can't vent, raising crankcase pressure and forcing oil past seals.

Which measurement determines whether a crankshaft journal needs to be ground undersize?

Answer: Journal diameter, taper, and out-of-round with a micrometer

Micrometer readings compared to specs determine whether journals must be machined.

A running compression test shows low readings on all cylinders at snap throttle but normal static compression. What is the most likely cause?

Answer: Restricted intake or exhaust breathing, such as worn cam lobes or a clogged exhaust

Running compression tests evaluate the engine's ability to breathe, revealing intake/exhaust restrictions.