How to Repair a Car’s Radiator

Most radiators eventually leak. The problem is that small pin hole-sized leaks are frequently hard to diagnose, and the leaks can be difficult to find. Some of these small leaks will only leak when they under pressure when the car is hot. Larger leaks are easier to find, but can be much more painful to repair. Repairing a car radiator can range from a small quick temporary fix to a complete radiator replacement.

If your radiator has a large crack or multiple leaks, replacement is almost always the better option.

Unless you can do the welding yourself, the labor costs of having major radiator repairs done can easily eclipse the price of a new radiator. The good news is that radiators are often not hard to replace as a do-it-yourself project. Usually, all that is required is to remove any parts that are in the way of lifting the radiator from the car along with the upper and lower hoses.

Cars with an automatic transmission may have cooling lines going into the radiator. Once the radiator is clear, you need to remove a few bolts at the top and maybe at the bottom and lift it out. Some radiators do not have any lower fasteners because they sit in a track or have rubber feet that go in holes to secure the lower portion in place.

Small leaks can be remedied temporarily in an emergency.

If you have purchased coolant that has stop leak properties, you may just need to add coolant and drive the car a couple of miles to let the coolant do the work for you. However, if you have a leak, there is a good chance that this means either the leak is too large, or you do not have stop leak coolant. There are two simple old remedies for small radiator leaks that work as long as the car is running with pressure on the coolant. Often when you shut off the engine, these temporary fixes let go and must be repeated.

Add about 2 tablespoons of mustard to your coolant. The mustard will migrate to the leak quickly and make an instant seal. The surplus mustard will melt into your coolant and just go away. The second solution is to add black pepper to the radiator. Like the mustard, this will require about 2 tablespoons of pepper. Both of these remedies are available in packets at fast food restaurants. They are temporary fixes until you can get somewhere for a permanent solution.

A good grade of stop leak will make a permanent fix for small leaks.

There are probably 10 or 15 different types of stop leak on the market. Most convenience stores and discount stores carry these products. All auto parts outlets will have multiple types of stop leak. It is a good idea to read the directions before making a purchase. Some stop leaks may not be compatible with all types of coolant.

The choice of stop leak is usually just a matter of personal preference.

While some people will sing the praises of one type of stop leak over all of the others, almost all brands of stop leak work equally well. All of them also have the potential to create problems in the heater core of your car. You do not want to do use too much stop leak. Do not operate under the idea that if one is good, two are better. Use the recommended amount only.

For aging or damaged radiators, stop leak may not be enough.

Auto parts stores carry products that can repair cracks and larger holes in some radiators. Most of these are some form of resin or epoxy. Usually, the bonding agent will require that you give the area being repaired a good cleaning before applying the fix. Some of these materials take a while to cure and may put your car out of business for a day or so. Try not to rush the job because many of these sealants do not bond to themselves. So, if you try to put pressure on the fix before it is ready, you will still have a leak. Unfortunately, it can be much harder to scrape out the old material than to have just waited long enough before testing it.

Cracks may require welding or other physical repairs.

Large cracks really should be welded to make the repair permanent. The problem is that large cracks only appear in old radiators unless you have had an accident. Having an old radiator means that even if you repair the crack, a new one is likely to form some place else. It is best to replace a radiator with large or numerous cracks.