Lesson 6: The Cooling System

This lesson is about the cooling system for the engine. A cooling system is needed to dissipate excess heat created during the internal combustion process. It accomplishes this with coolant and a radiator. The coolant travels through channels in the engine and captures excess heat, then the coolant travels to the radiator where the heat is released.

Cooling system maintenance is preventive maintenance to avoid an overheating situation and to avoid electrolysis (the breakdown of metals that occurs inside the engine block). Cooling system maintenance mileage varies by make and model. In some cases maintenance is necessary before the mileage indicated in the owner’s manual. For example, if the manufacturer recommendation is a coolant flush at 150,000 miles, it could easily need to be flushed before that. If the coolant is low then there may be a leak. Leaks can occur at a water pump, heater core, hoses, radiator, and at multiple locations throughout the engine.

The coolant is inspected at every oil change (about every 5,000 miles) and when it is found to be dirty then a cooling system flush is necessary. Typically the coolant gets dirty when non-distilled water is mixed with it. The impurities in the water cause corrosion (breakdown of the metals in the engine), which collect with coolant. This can clog radiator and cooling passages. That’s why coolant is mixed with distilled water where these impurities are absent.

When checking the coolant at home, be sure to never open the radiator while the engine is hot. (Remember Lesson 2, checking fluids).

How to flush the cooling system:

• Refer to the owner’s manual for locations of each part of the cooling system
• Open the radiator drain to drain the cooling system and collect the drainage into a container (you can take this to your local auto parts store for recycling)
• Remove the thermostat. The thermostat is typically on the engine side of the upper radiator hose, but in some cases it’s on the lower hose.
• Disconnect the lower radiator hose, force coolant through the thermostat housing (upper hose and engine block) with a garden hose until the water runs clear
• Connect the garden hose to the radiator, flush water through the radiator until the water runs clear.
• Completely drain the cooling system of all the water.
• Reinstall the thermostat
• Disconnect the reservoir and flush with garden hose until water runs clear. Completely drain reservoir.
• Connect the hoses and close the drains.
• Fill the cooling system with new coolant to manufacturer’s specification and distilled water. Use a 50/50 mixture of coolant and distilled water or pre-mixed coolant.

Flushing the cooling system will not correct an overheating concern. If your vehicle is overheating (as indicated on the temperature gauge on the dash), it would need to be diagnosed and repaired.

Any time you open the cooling system and put it back together you want to pressure test the cooling system to check for any leaks. You can use a pressure tester which can be rented from the auto parts store. It will come with instructions. Generally, it attaches to the radiator where the radiator cap goes, and you pump it by hand until the pressure on the gauge matches the pressure that is written on top of the radiator cap. Typically on a modern vehicle this pressure is between 13 – 16 psi. Let the vehicle sit with this pressure for 20 – 30 minutes. Then inspect the entire cooling system for any leaks and check the gauge for a change in pressure. If there is less pressure than before then there is probably a leak.

Lesson 6: The Cooling System is one of twelve lessons that are also available as a free ebook download which is complete with illustrations. These lessons are based on the outline for the Boy Scout Automotive Maintenance merit badge and adapted by Crawford’s Auto Repair for a general audience. This article is for informational purposes only and the author does not assume responsibility or liability for any accident that may occur when working on motor vehicles. By reading this page you accept the condition that you are ultimately responsible for your own actions. For additional information on the topics on this page see The Cooling System, Radiator Repairs.

Copyright © 2014, Jeff Crawford. Permission is granted to republish this article for personal or commercial use as long as the content, citation, and copyright notice all remain intact and unchanged. There must be an active “follow” link to CrawfordsAutoService.com.

Lesson 6: The Cooling System is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.