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Radiator Hose Collapse: How to Diagnose It

an upper radiator hose - Radiator Hose Collapse

Radiator hoses are a vital part of the cooling system that carry hot coolant from the engine through the radiator and circulate it back — cooler — to the engine again. There are two hoses, the upper and lower, and they’re thick and sturdy enough to handle both high pressures and immense heat. It should therefore strike you as odd if you notice one or both have collapsed. Don’t panic, however, as radiator hose collapse is usually a straightforward fix.

Nothing Happens in a Vacuum…Except When it Does

First of all, it’s important to note that some engines are designed to push coolant through the top hose, the radiator and then out the bottom hose. In others, however, the pump is placed to circulate coolant in the opposite direction, through the bottom of the radiator. This means one side (where the pump is) is the higher pressure side. Knowing how your cooling system is laid out will help you diagnose issues later on. Depending on the problem, one or both hoses can become flattened, and there can be different contributing factors. First and foremost, though, a collapsed radiator hose is the result of a vacuum condition. Usually, this is caused by a clog or constriction somewhere in the system.

Signs of Trouble

Radiator Hose Collapse: What is Happening Here?Maybe it only happens at high speeds or during engine revving, or maybe you notice it under the hood when the engine is cool. Perhaps an overheating engine prompted you to root around in the first place. A collapsed radiator hose doesn’t always make itself known, so it’s best to be vigilant and look under the hood every now and then. Engine overheating is not necessarily a cause or effect of a collapsed hose.

Causes and Fixes

The most common cause for radiator hose collapse is a vacuum issue caused by a faulty radiator cap. Caps are rated around 14–16 psi. Under normal circumstances, caps should release the negative pressure caused when an engine cools down and the liquid coolant contracts. They do lose their rating after years of use or sometimes they simply become too dirty to work. In these cases, all it takes to fix the issue is a new cap. Just make sure you replace the old one with new cap of the same pressure rating. Another common problem is clogging of the smaller radiator runoff hose, which leads to the coolant tank. As the engine cools, if fluid cannot return to the tank, this will also cause a vacuum. Additionally, it is possible that your radiator is clogged or dirty, but if that’s the case, you’re likely to have some overheating. Remember: Never open or remove a radiator cap from a hot engine.

Hose Condition

Just because the hose is collapsed doesn’t mean it’s bad, but you should always double check. If the hose is easy to pinch together, feels loose or sticky or looks cracked, it’s time for a replacement. Many times hoses come with an internal spring that maintains their shape, even in a vacuum situation, so don’t be surprised if a broken or missing spring allowed the collapse in the first place. Changing a hose isn’t too hard, but it can be messy. Be prepared to drain all your coolant in the process.

Always keep safety in mind when dealing with the cooling system. Beware the dangers of hot coolant under pressure and take-no-prisoners fans. If you’re unfamiliar with cooling systems, it’s best to consult your local NAPA AutoCare before moving forward.

Check out all the belts and hoses available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on radiator hose collapse, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Blair Lampe View All

Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter.  In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.

One thought on “Radiator Hose Collapse: How to Diagnose It Leave a comment

  1. Had same problem,top hose collapse, finally got it fixed, if you look right below thermostat there is a “1/2 hole in the pump housing.
    Someone tapped a “1/4 thread in it and put a plug in it. This Has to be open, took plug out works perfectly.

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