Your car’s coolant leak clearly indicates a coolant system issue. Since the coolant system comprises many components, anything can be faulty.
But why does the coolant leak after sitting overnight? What components are faulty? Among all the components, the culprit might be the following.
- Radiator issue
- Coolant hose leak
- Heater core issue
- Loose hose clamp
- Damaged water pump
- Gasket and seal leak
That’s not all. You have to learn how they cause the leak in your cooling system. In this guide, I will discuss the reasons in detail and talk about the ways you can fix them. Let’s detail the issue.
Coolant Leak After Sitting Overnight | Causes and Fixes Discussed
As I mentioned earlier, different reasons can cause the leak in the coolant after your car sits overnight. Let’s see the reasons in detail here and how you can fix the issue in the most effective ways.
1. Radiator Issue
The car radiator passes the coolant into the engine to keep the engine cool throughout the operation. You can consider the radiator as the heart of the cooling system.
Most of the time, a small leak or damage in the radiator causes a coolant leak overnight after you park the car in your parking lot. Besides, a faulty radiator is also a primary cause of coolant coming out of overflow tank.
Symptoms and Solution
If the radiator has small damage or leak, you will see a puddle of coolant underneath the car in the morning after parking the car overnight. Engine smoke and bubbling in the radiator can also be seen.
Since the crack or leak is small at the beginning of the radiator, you can apply an epoxy-resin sealer (I recommend J-B Weld 8277 WaterWeld Epoxy Sealer) to seal the crack or leak on the radiator.
2. Radiator Coolant Hose Leak
The coolant hose connects the radiator to the engine to flow the coolant to the engine.
Over time, heat, dirt and debris, age, etc., deteriorate the coolant hose. As a result, small leaks and damages develop over time.
Symptoms
Since the leak is smaller, you may not notice them soon. But, when you park your car overnight, you may see coolant pouring out of bottom of car overnight.
Diagnosis and Solution
- If you check, you will notice a moisturized and spongy radiator hose(s) when the hose is damaged. Check both upper and lower radiator hoses.
- Along the way, you’ll notice little droplets of coolant around the engine area. If so, the radiator hose is leaking or damaged, and you must replace it.
- Remove the damaged radiator hose (upper or lower), and attach the new hose in the same way the previous one was.
- The replacement will cost you anything from $150 to $250, based on the model of the car.
See the following video on how to replace the radiator hoses.
3. Loose Radiator Hose Clamp
You might be lucky because the radiator hose might not be faulty, damaged, or leaked. This might be only the radiator hose clamp, which is loosened over time.
If the radiator hose clamp is loosened, your car may leak coolant while sitting overnight. And you know what? This is one of the most common reasons for coolant leaks after sitting overnight.
Aging, abrasiveness, etc., can loosen the clamp.
Diagnosis and Solution
- Check for all the clamps on the upper and lower hoses. You have to check 4 connection points in the engine and the radiator for the two hoses.
- If any of the clamps is loosened, tighten it.
- You can pry it with a flathead screwdriver if it is a spring clamp. If it loses its precision, use a new clamp.
- If it is a worm-drive hose clamp, tighten the screw using a flathead screwdriver.
In the following video, see how a spring hose clamp works.
4. Heater Core Issue
The heater core is connected to the car’s cooling system, taking hot coolant and heating the car’s cabin. It is a small radiator that does the same task as the main radiator inversely.
But when the heater core is damaged a little, it can leak coolants overnight when you put the engine off.
Symptoms and Solution
If the heater core is leaking or damaged, you will experience the following symptoms.
- The windows will be foggy while running the car.
- You will get a sweet smell inside the car’s cabin when you turn on the heater.
- The coolant inside the overflow tank will decrease, and the car’s carpet behind the dashboard will be damp due to a coolant leak.
In this case, you should replace the faulty heater core. It is a pretty complicated task. So, you should rely on a professional for this.
See the following video on how to replace the heater core.
5. Damaged Water Pump
The water pump ensures the coolant keeps moving throughout the cooling system, from the radiator to the engine block and others. Expectedly, water pumps hold the coolant most of the time.
When the water pump is slightly damaged, the coolant will leak overnight, but you won’t notice this while running.
Symptoms and Solution
- If the water pump is damaged, you will hear a high-pitched and harmonic whining sound from the water pump while the car is running.
- You will also see steam come from the engine.
If so, you need to replace the water pump. To replace the water pump, follow the steps below.
Step 1
Open the hood.
Step 2
Disconnect the battery, the negative one, followed by the positive one.
Step 3
Remove the water pump belt and pulley.
Step 4
Keep a drain pan under the water pump.
Step 5
Now, remove the bolts to remove the water pump.
Step 6
Let the existing coolant fall on the drain pan.
Step 7
Now install the new water pump and reinstall all the components in a reverse manner.
Water pump replacement will cost you anything from $200 to $1,000, based on the car brand.
See the following video on how to replace the car’s water pump.
6. Blown Head Gasket
The engine head gasket is situated between the engine block and cylinder heads. It is the seal that keeps the fluid and coolant from leaking.
When the engine head gasket is leaked, coolant can leak overnight. If the gasket damage is minor, you may not notice the coolant leak around the day. But, coolant keeps leaking over the night when you keep the engine off in your parking.
Symptoms and Solution
The most highlighted symptom of a worn-out head gasket is discolored engine oil. It happens because the engine oil and coolant get mixed due to a broken head gasket.
Aside from this, you will experience white smoke and engine overheating while driving.
Fixing the blown head gasket is a pretty complicated task. You must consult a professional auto mechanic to replace the head gasket. It will cost you around $1,000 to $3,000, which is pretty expensive.
Final Words
The car’s coolant leak after sitting overnight is an indication of the leaks in the cooling system. Some of the issues are pretty easy to fix.
However, some are complicated and need professional treatment. If you experience a coolant leak issue overnight, don’t be late. Consult the nearest auto mechanic shop to fix the issue.
