Heating and Cooling Flashcards

A cooling system holds pressure poorly during a pressure test, but no external leaks can be found. Technician A says the head gasket could be leaking. Technician B says the heater core could be leaking. Who is correct?

Answer: Both A and B

A pressure loss with no visible leak can come from an internal head gasket leak or from a heater core leaking into the cabin.

Why is a refractometer preferred over a float-type hydrometer for checking coolant?

Answer: It reads accurately for both ethylene and propylene glycol

A refractometer gives accurate freeze-point readings for both glycol types, while hydrometers are calibrated for ethylene glycol only.

What happens if the coolant mixture is more than about 70% antifreeze?

Answer: Freeze protection and heat transfer both get worse

Above about 70% glycol, freeze protection actually gets worse and heat transfer drops, which can lead to overheating.

Why does the lower radiator hose often have a coiled wire spring inside it?

Answer: To keep the hose from collapsing under water pump suction

The lower hose is on the suction side of the water pump, so the spring keeps it from collapsing at high RPM.

What is the typical recommended service interval for long-life OAT coolant?

Answer: 5 years or 150,000 miles

Extended-life OAT coolants are commonly rated for about 5 years or 150,000 miles; always follow the OEM schedule.

When pressure testing a cooling system, the test pressure should be:

Answer: The pressure stamped on the radiator cap, not above it

Testing at the cap's rated pressure finds leaks without risking damage to the radiator, hoses, or heater core.

A technician uses a float-type hydrometer to check a propylene glycol coolant. What will the result be?

Answer: An inaccurate reading because of the different specific gravity

Propylene glycol has a different specific gravity than ethylene glycol, so a hydrometer reading will be wrong.