How to Seal a Car Radiator

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A car radiator can leak in the tank, the core or in the radiator hoses, and a crack in the aluminum or plastic parts can't typically be repaired. Learn about fixing a leaking radiator along the seam with help from an ASE-certified master automobile technician in this free video on car radiators.

Part of the Video Series: Auto Repair & Maintenance
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Video Transcript

It's always annoying to come out to your car in the morning and find a green puddle coming out from underneath it. One possible source of a problem like this is the radiator leaking itself. There's several possible reasons why a radiator might leak itself. We have to first look about how a radiator typically today is built. Most modern radiators we find that the actual cooling part, the part they call the core, has aluminum tubes with fins built in it. And these horizontal lines that we see here where the coolant actually goes through, and this is attached to a plastic tank where there are actual radiator hoses attached to it. So there's basically three places that things can leak. It could either leak in the core area, somewhere in here or at the edge of this, which is more often than not caused by an impact of something. Piece of dirt in the road or stick. Something of that nature. It could leak in the tank area. These plastic tanks, when they get old they have a tendency to become hard and will develop cracks and it could leak in this area. And then there's the area where the two of these things join together. The area in between the plastic and the aluminum is actually sealed with a large O-ring that goes around the whole perimeter and which is typically made out of rubber. If you have a leak in the core area these in many cases are not repairable at all. You can't really solder to aluminum and the prospect of welding it is typically not very good either. If you develop a crack in the plastic area that's typically not too well repairable either. They do sell some products on the market that are epoxy based and those can help to seal up the holes but as a professional I'll tell you that the likelihood of this being a permanent repair is pretty unlikely. And so if we find a crack we generally recommend a radiator replacement. The other place that they can leak is actually at the seam where the two parts of the radiator come together. In these circumstances we find that with an older radiator they will typically leak when it gets cold out. When the rubber shrinks and the antifreeze can come out. In circumstances like that sealing products can help. A typical sealing product that has been put into cars for probably more than 50 years, cooling system tablets are actually made out of crushed pecan shells, and if you add these into your cooling system, when this part of it leaks out it can actually help to plug up the leak in the seam area. But other than that, a crack in the tank or a puncture in the core area really the radiator should be replaced.


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