While there are still a few air-cooled automobiles on the roads the good majority out there these days are of the liquid cooled variety. Those driving an old Karmann Ghia or a pre-98 Porsche 911 can take the time spent reading this series of articles on the automotive cooling system and instead check their oil frequently. The rest of the liquid cooled vehicle owners out there have three important components under the hood that take the heat out of an internal combustion engine. The radiator, the water pump, and the thermostat. Between all of these components are flexible rubber hoses that transfer the liquid engine coolant.

Cooler Heads

The burning of gasoline, diesel, or corn cakes, produces heat from the instant an engine starts. This heat must be channeled away so the engine can keep spinning instead of fusing itself together. Surrounding the cylinders in which the pistons and valves do their internal combustion act is a jacket that contains engine coolant. The coolant transfers heat from the engine and is then circulated through the cooling system by way of a water pump. Coolant travels out of the engine, and through one rubber hose into the radiator. The radiator allows heat to pass from the coolant into the surrounding air, and presto! The coolant returns back to the engine through another rubber hose cooler than when it left.

Circulating Coolant

In this way the engine keeps cool. In a brilliant stroke of engineering, the automobile heating system utilizes a smaller radiator of sorts called a heater core. Smaller rubber hoses bring hot coolant from the engine into to the heater core. This miniature radiator along with a blower fan keeps toes and kiesters toasty in winter. So it goes. Over time this cold and hot act takes its toll on engine coolant and components. Heat unleashed by the radiator and engine itself especially beats up on the rubber the radiator and heater hoses are made out of. Trouble can come if either one of the radiator hoses cracks or starts leaking. Cooling system pressure and coolant can quickly escape and cause big problems fast. Engine overheating is the number one cause of cylinder head failure. Overheating can be caused by the failure of a ten buck hose, 37 cent hose clamp, or as we'll examine next week - a seven dollar thermostat.


Hose Inspector

Inspecting the radiator and heater hoses once a year or so is not only easy, it can prevent spending that summer afternoon pic-a-nic on the side of the road waiting for a tow, instead of down by the lake with the basket. Obvious signs of impending hose failure is coolant seeping from the hose itself. In some cases hoses will present a miniature version of Vesuvius. That radiator hose that looks like a snake that swallowed a rabbit will blow shortly, usually on the way to a job interview or to pick up a pal from the airport. Less obvious signs of decay can be seen and felt by grabbing hold of a cold radiator or heater hose and giving it a good squeeze. Brittle or cracking material, a spongy feel, or a hose sticking to the inside of itself are bad signs. Replacement radiator hoses for even the most obscure of automobiles are available from your neighborhood or online auto parts store.

Up Front

Since most sane automobile engineers place the radiator up at the front of the vehicle for superior heat transfer and engine cooling, replacing the radiator hoses is usually an easy job. Heater hoses, being smaller in size and trickier in routing, can present more difficulty. The best time to inspect your heater and radiator hoses is cooler weather. Ever notice how the first warm day of the year brings masses of steaming over motorists on road shoulders? An on the edge of failing cooling system or radiator hose will be fine during winter but give up at the first sign of hot weather. Never grab onto a hot radiator hose or attempt to remove a radiator cap from a hot radiator. The resulting steam can cause serious injury. Keep an eye on hoses until next week, when we move inside the cooling system.


Next Week: Replace a Thermostat

Stuff You'll Need:

· Replacement Radiator and/or Heater Hoses
· Radiator Hose or White Lithium Grease
· Hose Clamps
· Utility Knife
· A Clean Catch Container
· Pliers or Hose Clamp Pliers and Hand Tools
· Funnel
· Ramps and/or Jack Stands
· Coolant
· Distilled Water


Disconnect the negative battery post. Allow engine to fully cool. Remove the radiator cap. Locate the radiator drain valve, usually on the bottom corner of the radiator. Turn the valve to drain the engine coolant. Close valve. Use a clean catch container. Keep one container for coolant, and the other for oil. If the coolant is still OK pour it back from where it came after hose replacement.


Loosen radiator hose clamps. Move the hose clamps towards the center of the hose. The pictured clamps are of the original equipment manufacture [OEM] variety circa 1982. Screw-type worm-drive hose clamps may also be found or used as replacements.

The quickest way to remove stuck-on or crusty old radiator hoses for replacement is utility knife surgery. Slice lengthwise and peel hose away. Don't go Gorilla Monsoon trying to remove the hose. The necks on the radiator and aluminum thermostat housings are often fragile from age.


Transfer hose clamps to new hose. Compare old and new hose. Trim if required. Take a little off rather than a lot. Better a little too long than too short! A little radiator hose or white lithium grease will help with installation. Grease also prevents corrosion and makes for less difficult removal next time around. Just put a dab where the hose meets its mounts.


Don't forget to put the hose clamps on the hose before installation. Slide hose into place. Attach or tighten hose clamps. Do not over-tighten screw-type worm-drive clamps! OEM style clamps create their own tension. Remove and install heater hoses the same way.

If the coolant looks OK return it to the cooling system. If the coolant looks like it came from the big lake they call Gitche Gumee, dispose of old coolant properly and refill the radiator a 50-50 mix of new coolant and distilled water. Minerals in tap water can contribute to cooling system corrosion buildup. Fill radiator 3/4 or so full. Start engine. Slowly top off radiator with engine running to burp any trapped air from the cooling system. Replace radiator cap. Check overflow tank level.


And You Will Know Us by the Trail of Parts [Internal]