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Radiator And Pressure Cap

Radiator and Pressure Cap

When overheating problems occur and the system is not leaking, check the radiator and pressure cap. They are common sources of overheating. The pressure cap could have bad seals, allowing pressure loss. The radiator may be clogged and not permitting adequate air flow or coolant flow.

Bent fins should he straightened and the radiator core checked for any obstructions tending to restrict the airflow. Radiator air passages can be cleaned by blowing them out with an air hose in the direction opposite to the ordinary flow of air. Water can also be used to soften obstructions before applying the air blast. In any event, the cleaning gets rid of dirt, bugs, leaves, straw, and other debris which otherwise would clog the radiator and reduce its cooling efficiency. Sometimes screens are used in front of the radiator core to reduce this type of clogging.

The radiator can be checked for internal clogging by removing the hose connections and draining the coolant. Use a garden hose to introduce a stream of water into the top of the radiator. If the flow is sluggish, the radiator is partially clogged. Another way to check for this condition is to feel the radiator with your hand.

The radiator should be warm at the bottom and hot at the top, with the temperature uniformly increasing from bottom to top. Any clogged sections will feel cool.


Be sure the engine is not running when making this test to avoid injury from the fan.

When the use of cleaning compounds and reverse flushing fails to relieve a clogged core, the radiator must be removed for mechanical cleaning. This requires the removal of upper and lower radiator tanks and rodding out the accumulated rust and scale from the water passages of the core.

The radiator pressure cap should also be checked for condition and proper operation. If it is dirty, the cap can be cleaned with soap and water, then rinsed. The seating surface of the vacuum and pressure valves should be smooth and undamaged The valves should operate freely when pressed against their spring pressure and should seal properly when closed.

During the vehicles preventive maintenance (PM) inspection, the radiator should be checked for leaks, particularly where the tanks are soldered to the core, since vibration and pulsation from pressure can cause fatigue of soldered joints or seams. Neglect of small leaks may result in complete radiator failure, excessive leakage, rust clogging, and overheating. Thus it is extremely important to keep the radiator mounting properly adjusted and tight at all times and to detect and correct even the smallest leaks.

A leak usually reveals its presence by scale marks or watermarks below the leak on the outside of the core. Permanent antifreeze does not leak through spaces where water cannot pass. The antifreeze leak is more noticeable, since it does not evaporate as quickly as water.

Stop-leak compounds can be effective to stop small leaks at least temporarily. Stop-leak compounds harden upon contact with the air, thus sealing off any small openings. The main problem is that they give the mechanic a sense of false security. For example, stop leak may prevent seepage at a hose connection through the inner lining, but finally the hose will rot and burst, losing coolant and overheating the engine.

Stop-leak compounds can lead to radiator clogging if water tubes already contain deposits that act as a strainer. If coolant level gets too low, some stop-leak ingredients may harden in the upper radiator and block it.


Before using stop leak, check your service manual. The compound must be compatible with the antifreeze and the inhibitors and must be installed correctly and in the right quantity.

When large leaks or considerable damage is present, removal of the radiator for extensive repair or replacement is usually required.

Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy

Copyright 2001-2004 SweetHaven Publishing Services
All rights reserved