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Finding a Coolant Leak

Radiator hose

Coolant leaks can be obvious or they can be a headache to locate. When coolant is leaking from the radiator or a split hose, it's likely easy to note where it's coming from and make a fix. When it's dribbling from some random point in the engine compartment or only occasionally steaming from an unspecified location to condense and drip from the hood.. not so much. Here are a few pointers to help find a coolant leak that's doing a good job of hiding itself.

The issue came up when user ddstif in our forums asked where coolant could be leaking from after his Suzuki began running hot and then "burned" (vaporized) coolant on its exhaust manifold.

In his case, it's coming from somewhere underneath the manifold towards the bottom of the engine, but where the coolant was manifesting and where it actually leaked from could be two different locations. As forum mechanic Big Block 409 pointed out.

Obviously, you should do all of the following checks when the engine is cooled sufficiently that you can place your hand on the radiator cap without it feeling too hot and should only be done when wearing proper safety gear and taking proper shop safety precautions.

The first step is to verify that the coolant is only leaking to the outside of the engine and not intermixing with oil or fuel. That's done with a couple of simple checks. Pull the dipstick and check the oil to make sure it's not "milky." Then check the exhaust to smell for the sweet tinge of antifreeze burning or white smoke indicating coolant is being vaporized in the combustion chambers. If all is well, your leak is likely only an external one.

Begin checking for external leaks from the more obvious locations. A pinhole leak can, when under pressure, send a lot of coolant out without making it obvious where it's coming from. The coolant in your engine follows a path that starts at the radiator and moves through the engine core and back. Following that path is the simplest way to find a leak. Most shop manuals and repair books will have a diagram of the engine coolant path.

Start with the hose from the radiator going out to the engine (lower hose). Make sure there is no leak in that hose and that it's in proper working order with good clamps and connections. Check its connection to the thermostat housing and that housing's condition and seal against the engine block. A small drip when the engine is cool can mean a spewing leak when the coolant is hot.

Water bypass and inlet pipes are the next likely culprits. These are usually located towards the center of the engine block and to one side (sometimes both sides). These are near the exhaust manifolds on most engine models and are the most likely leak point for our forum member's issue at hand. The most likely fail point are the compressed O-rings on these pipes that might have begun to deteriorate with time.

Hoses to and from the heater core are also likely leak points. These usually extend from the rear of the engine block into the firewall. These are usually rubber hoses and can have the same types of failures that any rubber hose can.

Radiator hose returning from engine, located to the top of the coolant radiator, is the final check. This hose could have leaks at its connection points or anywhere along its rubber surface.

If the leak point isn't obvious, adding some coolant dye to find the leak could help. Happy hunting!