The Skinny on Cooling System Hose Diagnosis and Replacement

Considering it’s the middle of winter, we might be a little late with this story. We know you’re smart cookies, though, and you checked your radiator and heater hoses before the weather turned. You did, didn’t you?

Inspecting and replacing radiator and header hoses isn’t complicated. The biggest issues, especially on newer vehicles, are accessing the darn things and wrestling with clamps. We’ll share some tips and tools to make the job easier. But first, let’s look at what causes hose to go bad.

Diagnosing Hoses
Radiator and heater hoses have to put up with a lot. They need to handle severe temperature swings and resist damage caused by coolant, oil, salt, ozone, and road debris. Cooling system hoses deteriorate with age, a process that occurs primarily from the inside out. If all of the cooling system hoses are about the same age, there is a good chance that if one is bad, some of the others are on the verge of failing as well. That’s why you need to inspect all of the hoses so you find all of the problems at one time.

The best time to inspect hoses is when the engine is warm. A hose in good condition should feel firm, but not hard. A failing hose will feel very hard, spongy, or soft.

Pay special attention to curves and bends. This is where cracking often occurs. Make sure hoses are not kinked, which can reduce coolant flow and cause overheating. Also check to see if hoses are touching sharp edges or hot/moving engine parts. Look for fraying near connection points as this is a common cause of leaks.

Some lower radiator hoses have an inner reinforcing coil or wire reinforcement. If it is missing or damaged, the lower radiator hose could collapse at high vehicle speeds and cut off coolant flow to the engine. A collapsed hose will often resume its normal shape at lower speeds or when the engine is off.

Signs of Hose Failure
These are the most common signs of a failing hose:

Electrochemical Damage (ECD)
Cause: Different kinds of metals in the cooling system generate an electrical charge, which is carried from one component to another by the coolant. This electrical charge creates small internal cracks which can weaken the hose.
Appearance: ECD damage is usually found in the first two inches from the hose ends. Squeeze the hose near the connectors; if the ends feel softer than the middle or you feel gaps or channels inside the hose, it is most likely due to ECD.
Solution: Replace the damaged hose. Most modern replacement hose is electrochemical-resistant to reduce ECD.

Leakage
Cause: Insufficient clamp torque, deterioration of the hose or connector, hose compression ‘set’ due to age.
Appearance: Moisture, drips, or coolant bleed marks on or around clamps, connectors, or on the hose itself.
Solution: Retighten adjustable tension clamps after a brief run-in period. Alternatively, use constant-tension clamps, which automatically adjust as the hose heats and cools. Connectors with a raised bead on the end(s) will seal better and reduce the chance of a hose slipping off.

Heat Damage
Cause: Engine heat, low coolant levels, and/or temperature spikes.
Appearance: Hardened, glossy, and cracked outer surface. Slight swelling is a sign of internal damage.
Solution: Replace the damaged hose.

Ozone Damage
Appearance: Tiny, parallel cracks on the outer surface, usually at bends.
Cause: Increased concentrations of ozone caused by pollution will attack bonds in certain rubber compounds. Tiny cracks occur, allowing contaminants to destroy the hose.
Solution: Replace the damaged hose with new hose made from EPDM rubber, which is not affected by ozone. Most modern replacement hoses are made from this material.

Abrasion Damage
Cause: Hose rubbing against other engine parts.
Appearance: Rub marks or damage to the outer surface.
Solution: Replace the hose if badly damaged. To prevent future damage, try rerouting the hose and/or use hose guides or a protective wrap. The OEMs often use guides and wraps to prevent hose damage; reuse the factory items if they are in good shape or replace with new ones.

Oil Contamination
Cause: Oil reacts chemically with rubber compounds and weakens the hose. This causes the hose to soften, swell, and separate layer by layer, leading to failure.
Appearance: The hose is soft or spongy to the touch. Bulges and swelling are readily apparent.
Solution: Replace the hose and either repair the oil leak or reroute the hose.

Other Tips
Hose temperature can reveal if the cooling system is functioning properly. You can use an infrared thermometer to read temperature. For example, when the heater is on, both the ingoing and outgoing heater hoses should be close to the same temperature. If not, it might be time for a repair. If the upper radiator hose gets hot before the engine has properly warmed up, it means the thermostat is not closing properly or is constantly open. If the hose does not get hot at all, the thermostat is blocked. In both cases, replace the thermostat immediately.

Hose Types
Modern radiator and heater hoses are made from synthetic rubber and other materials that resist damage from the nasties we listed above. Many hoses have reinforced areas for connectors and clamps and have an inner spring as required. Some hose comes as a complete assembly with the necessary clamps and connectors.

Preformed or molded radiator and heater hose is the most common, making replacement a simple R&R job. If you can’t find molded hose for your vehicle or you’ve done an engine swap, Summit Racing carries flexible radiator hose that can be bent or curved to fit. Flexible hose is universal, so some measuring is required to determine the length of hose you’ll need. Coils of universal-fit heater hose are available in various lengths and diameters.

Clamps and Fittings
If you’re replacing old hoses, you should replace the clamps too. New clamps aren’t expensive and are much easier to deal with than old and (most likely) corroded clamps. There are three basic types:

Worm gear clamps are the most affordable and come in lots of sizes. The clamps’ adjustment slots squeeze around hose as you turn the adjusting screw, creating the seal. Worm gear clamps don’t compensate for hose shrinkage as they age, and can dig into the hose itself. Both issues can create leaks.

Spring clamps are the most common OEM clamp. Made from spring steel, they apply constant tension to the hose regardless of condition, making them very reliable. The downside is working with the darn things; you have to squeeze the clamps apart to install and remove them, which is no treat if a clamp is fused to the hose or located in a hard to reach area.

T-bolt clamps come from the racing world. They have a smooth, solid band that provides a 360° seal without cutting into the hose like a worm gear’s serrated band does. Most are made from stainless steel for long life. T-bolt clamps can lose tension over time, and sizes are somewhat limited.

When you’re replacing heater hose, make sure to check the connectors and fittings. If you see corrosion or other signs of leaks, replace them too.

Flushing and Filling
Hose replacement is also a good time to flush and refill the cooling system. You can rid the system of rust and corrosion and replace old coolant with fresh stuff that has full-strength corrosion inhibitor additives to protect the water pump and other metal parts. Our friends at 2CarPros have an excellent article on how to do the job properly.

Tools of the Trade
Here are some tools that will make hose replacement and coolant system servicing easier:

Lisle Hose Remover Tools
Lisle Hose Cutters
OEM Hose Disconnect Tools (these also work on fuel and transmission lines)
Astro Pneumatic and Knipex Hose Clamp Pliers (perfect for those stubborn spring clamps)
Dorman Radiator Flush Kit
Performance Tool Coolant Tester
OTC Coolant Refiller
Lisle Spill-Free Coolant Funnel (keeps air out of the cooling system as you fill it)