How to Fix a Radiator

Co-authored by Jason Shackelford

Last Updated: March 23, 2024 References

If you are having an issue with the coolant system in your vehicle, one culprit may be the radiator. The radiator is designed to diffuse the heat the coolant absorbs as it travels throughout the engine, but low coolant levels caused by leaks or coolant that has gone bad can compromise your radiator’s ability to do so. If you are having issues with your radiator, there are a few things you can try yourself before resorting to having it professionally repaired. Remember though, an overheating engine can cause significant damage to internal components, so you may want to consider professional repair if the vehicle continues to have cooling problems.

Part 1

Part 1 of 3:

Identifying a Problem with Your Radiator

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1
Look for puddles beneath your vehicle. A sure sign that there’s an issue with your vehicle’s cooling system is finding a puddle of coolant under your vehicle. Remember that there are a number of fluids in your engine that could feasibly leak, so check closely to confirm if the puddle you find is coolant, oil, or possibly even just water from running the air conditioner.^{[1]
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- Touch the puddle with your finger, then wipe it on a white sheet of paper to see what color it really is.
- If it is green or orange, it’s likely a coolant leak.
2
Check the coolant reservoir. If you believe your vehicle may be leaking coolant, check the coolant reservoir in the engine bay. Most coolant reservoirs have “fill lines” labeled on the container that will let you know if the coolant levels are low in your vehicle. Check the coolant level in your vehicle and top it off with a water/coolant mixture if it appears to be low. Check it again after a few days to see if the level has changed.^{[2]
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- Make sure to check the coolant levels with the vehicle at about the same temperature each time (either warm from driving or cool from sitting).
- Dropping coolant levels in conjunction with puddles means a coolant leak is very likely.
- Check in the owner's or service manual for your vehicle to locate the coolant reservoir if you are unsure of where to find it.
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3
Pay attention to changes in your temperature gauge. If your engine is low on coolant, or the coolant needs to be changed, it will struggle to maintain a proper running temperature. Keep your eye on the temperature gauge in your vehicle. If it begins to run consistently warmer, or begins to overheat sporadically, there is an issue with your cooling system.^{[3]
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- Failing to adequately cool your engine could mean your coolant levels are too low.
- Coolant can eventually go bad. If the coolant levels are still high but the engine is overheating, one issue may be that the coolant needs to be replaced.
- If you are uncertain of what the symbols on your gauges mean, refer to your vehicle's owner's manual to determine which is the temperature gauge.
4
Visually inspect your engine bay. If you suspect that your coolant system may be leaking, spray the engine with a hose to remove any existing signs of a leak. Then start your engine and visually inspect the engine bay, looking closely for signs of a leak. Coolant is usually under pressure, so a leak could spray out or it may only trickle. Wear safety glasses and exercise caution while looking around the engine bay with the engine running.^{[4]
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- Do not put your hands inside the engine bay with the engine running.
- Look for any new signs of coolant leaks then follow the coolant to the highest point to locate the crack or hole.

Part 2

Part 2 of 3:

Draining and Flushing Your Radiator

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1
Allow the engine to cool completely. The coolant system is under pressure while heated and opening the radiator cap or petcock while the system is under pressure could result in serious burns. Allow the car to sit for a few hours to make sure it’s completely cool before coming into contact with any parts of the coolant system.^{[5]
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- After a few hours, lightly tap the top of the radiator to see if it is cool to the touch. If it’s warm, the coolant inside may still be quite hot.
- Opening the coolant system while hot will result in heated coolant spraying out, which is extremely dangerous.
2
Jack up the vehicle. In order to access the bottom of the radiator to drain the old coolant, you’ll need to raise the vehicle to a height that allows you to work and place a container beneath it to catch the draining fluid. Locate the designated jack points for your vehicle by consulting your owner’s manual to avoid doing any damage to the vehicle while you jack it up.^{[6]
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- Once the vehicle is high enough to slide your container underneath it, place jack stands beneath it to support the weight of the vehicle.
- Never work under a vehicle that is supported only by a jack. Jack stands will prevent the jack from losing pressure and lowering the vehicle while you’re beneath it.
3
Open the petcock and drain the coolant into a container. Locate the petcock on the bottom portion of the radiator. The petcock often looks like a spout with a valve you can turn to open it, and it should be on or near the bottom of the radiator to allow it to drain. Once you have located it, make sure the container is positioned properly beneath it and open the valve.^{[7]
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- The coolant should be cool coming out of the radiator, but you should still take care to avoid letting it come into contact with your bare skin.
- Check your owner’s manual for the vehicle’s coolant capacity and make sure you have a container large enough to hold it all at least twice.
4
Flush the radiator using a hose. Once you’ve finished draining the radiator, there will still be a great deal of bad coolant remaining in the system. Close the petcock and fill the coolant reservoir with water. Start the engine and allow it to run for a few minutes before draining the radiator again. You should repeat this process two or three times.^{[8]
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- If you only allow the engine to run for a few minutes each time, it should not get too warm to drain the radiator.
- The water will flush out the rest of the bad coolant from the engine.
5
Refill the radiator with a water and coolant mixture. Most vehicles require a 50/50 water and coolant mixture to maximize the coolant system’s efficiency. You can purchase pre-mixed coolant, or choose to mix it yourself. Fill the reservoir until it is an inch above the “full” line, then start the engine. As it warms up, the thermostat will open, allowing coolant to flow in. As the coolant level drops in the reservoir, continue to add to it. Add the mixture to the radiator or reservoir until you reach the maximum suggested capacity.^{[9]
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- If you do not have your owner’s manual, check the vehicle manufacturer’s website for fluid capacities.
- It may take a few minutes for the coolant to drain into the system, so be patient as your pour the new coolant in.
- If your vehicle’s radiator has a bleeder valve on the top, open it and allow the engine to run for ten minutes to allow any excess air to escape.

Part 3

Part 3 of 3:

Sealing a Leak in Your Radiator

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1
Replace the radiator cap. A common point of failure on radiators is the cap itself. Radiator caps are designed to allow excess pressure to escape to avoid damage to the coolant system, but over time they can become oxidized, full of grime, or just worn out. To replace your radiator cap, simply wait for the engine to cool completely and twist the old cap off. Screw the replacement on in its place. ^{[10]
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- You can purchase replacement radiator caps at your local auto parts store.
- Make sure to ask for a cap that fits your vehicle’s exact year, make and model.
2
Use a commercial leak sealant. Commercial leak sealants are sold at most auto parts stores and can help resolve a radiator leak if you’re in a bind. However, it’s important to note that these leak sealants aren’t designed to be permanent repairs. To use a leak sealant, simply open the radiator cap on a cool engine and pour it in. Top off the radiator with a coolant and water mixture if it is low as a result of the leak ^{[11]
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- You will likely still need to locate and repair the leak, or replace the radiator after using a leak sealant.
- Leak sealant is a great option if you need to get your vehicle home or to a repair facility.
3
Seal visible cracks with epoxy. If you are able to locate a crack in your radiator, you may be able to repair it using an epoxy. First clean the area around the crack thoroughly, as any dirt or grease may prevent the epoxy from establishing a seal. Use a spray on brake cleaner and a rag to remove any stuck on grime, then allow the cleaned area to dry completely. Use your hands to knead the epoxy until it becomes malleable enough for you to spread it out over the entire crack.^{[12]
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- Allow the epoxy to set overnight before starting the vehicle.
- Radiator epoxy can be purchased at most auto parts stores.
4
Replace the radiator. If there is a crack in your radiator, it is highly likely that you may need to purchase a replacement for it. To replace your radiator, drain all of the fluids from it and disconnect the hoses leading into and out of the radiator. Unbolt the brackets that hold the radiator in place and slide it up and out of the front of your vehicle. Different vehicles will have different mounting hardware, but it’s common for radiators to be held in place by four to six bolts. Slide the new radiator into place and secure it using the same bolts.^{[13]
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- You may have to remove body or trim panels to access the radiator bolts or to remove the radiator from the vehicle.
- You can purchase a new radiator from the vehicle manufacturer or most auto parts stores.
EXPERT TIP

Hovig Manouchekian
Auto Repair & Design Specialist
Hovig Manouchekian is an Auto Repair and Design Specialist and the Manager of Funk Brothers Auto, a family-owned business operated since 1925. With over 30 years of experience in the automotive industry, Hovig specializes in the process of auto repair and maintenance. He is also very knowledgeable in common automotive issues and needs including engine repair, battery replacement, and windshield accessory and maintenance. Hovig's knowledge and hard work have contributed to Funk Brothers Auto winning Angie's List Super Service Award for five consecutive years.

Hovig Manouchekian
Auto Repair & Design Specialist

Be sure to accurately measure your current radiator before buying a replacement. Use a tape measure to determine the radiator core's length, width, and depth. Also, note the number of core rows (horizontal channels) in the radiator. Aim to find a replacement with the same or more core rows to ensure optimal cooling efficiency.

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When should you change your radiator fluid?

Jason Shackelford
Auto Technician
Jason Shackelford is the Owner of Stingray Auto Repair, a family owned and operated auto repair shop with locations in Seattle and Redmond, Washington. He has over 24 years of experience in auto repair and services, and every single technician on Jason’s team has more than 10 years of experience.

Jason Shackelford

Auto Technician

Expert Answer

Most types of radiator fluid should be changed out every 30,000 miles, but this can vary.

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