Most of my viewers that are experiencing bad issues with their car’s cooling system, often asks me about the signs or symptoms of a failing or bad radiator.
Since I already replaced mine with a new one, I do have a lot of experience dealing with overheating problems especially with regards to failing radiators. So if you believe that your radiator is already going bad, then I can truly help you to figure out the culprit.
Read on and learn the seven common symptoms of a bad or failing radiator.
7 Signs of a Bad Radiator
A failing radiator is sometimes tricky as you really can’t tell if the culprit is the radiator or other parts of the cooling system.
So you still have to diagnose everything before you can truly identify why your car overheats. I detailed every bit of possible reasons why car overheats in this blog post.
Your car could still run in low speed and have no issues with your cooling system, but will overheat when you drive hard and accelerate fast. Others will even overheat when the car is in idle.
Whatever the scenario is, there is one thing that you are certain – your car has a cooling system issue and you need to know if you have a bad or failing radiator.
So to ease your headache, I will give you seven common signs of a bad radiator. Read on!
Coolant Leaks
Cooling system leaks can come from many areas such as hoses, engine block gaskets and of course, radiator. Minor leaks are often caused by damaged hoses and loose clamps. But if your radiator is leaking, you will notice significant amount of coolant loss.
Radiators have housing (which is usually made of hard plastic) and cooling fins, both of which are the common areas where leaks occur.
Overtime, radiator housing pops out or gets blown by severe pressure inside the radiator which causes coolant to escape. If this is your issue, then you have to either use a metal epoxy or just install a new radiator.
If the radiator housing is not leaking, then take a closer look at the fins. Leaking fins are caused by outside debris that hits your radiator while driving in a high speed, or just too much rusting. You can use stop leak products to help fix this issue. Otherwise, radiator replacement is necessary.
Your Car Overheats Only When You Speed Up or Going Uphill
A failing radiator can still function when you don’t drive hard. But if you start to speed up, your temperature gauge will also increase beyond normal (normal temperature is between 84 to 95 degrees C).
This means that your radiator is the culprit as it is most likely clogged, which is the number one reason why radiators are going bad.
A slightly clogged radiator can still allow the coolant to flow into and out of the radiator. But once your accelerate, the coolant flow also increases as the pressure from the water pump also increases.
If the radiator is slightly clogged or clogged, you will experience overheating when going uphill or driving in high speeds.
Coolant Discoloration
To make the car engine functional, it should have an efficient and quality coolant that circulates in the entire cooling system. Any disruption to this flow will affect your car engine’s temperature and performance.
So the first thing that you should know is the color of your coolant, which varies on the car brand, make or model. Most cars use green coolant, but there are also other color variants such as pink, orange, red, blue and blue.
When you see that there is a significant discoloration on your coolant, then it is a sign that you have either a rusty radiator, or an even worse case of oil and coolant contamination.
Rusty coolant will turn to a more rusty color, and coolant with oil will be colored black or darkened type of color and will be thicker than ordinary coolant.
Discoloration occurs when your radiator has leaks internally, where transmission fluid are being cooled (this is called transmission cooler).
Automatic transmission fluid also passed through the radiator, so if your radiator has leaks inside, it will get mix with the coolant. This will not just overheat your engine, but also damage your transmission that will result to shifting issues or overheating of transmission.
Rusting occurs when you don’t flush your coolant in a regular basis. Overtime, your coolant looses its capacity to reduce or transfer heat, negating its natural properties and will result to internal rusting.
To avoid this, you should only use proper mixture of coolant and distilled water and must be flushed according to its maintenance schedule.
Hot Lower Radiator Hose
Another good way to check if you have a failing radiator is your lower radiator hose. To be able to see the picture, you need to understand how coolant flows inside the system.
When you start your car, coolant will not start flowing unless the thermostat opens. Thermostat is a device that acts like a valve that prevents the coolant inside the engine block to escape to the radiator.
It has a temperature-sensing mechanism where it automatically opens once it reaches high temperature, or in Layman’s terms, once your engine reaches operating temperature.
Once the thermostat opens, the hot coolant will now free to flow into the radiator through the lower hose, which will be cooled by air. The stock cold coolant inside the radiator will then exit through the upper radiator going into the block, that will help cool the engine’s temperature down.
Some car models have coolant flow completely in reverse from this set up, so make sure to study your engine’s make up.
So that’s how the coolant flow inside the cooling system, and will continue to cycle through the course of your driving trip.
However, your engine will overheat once this flow is interrupted by either a coolant leak or a clog. And you can easily tell if your radiator is the problem by just touching the lower and upper radiator hoses.
If your lower hose is extremely hot while the upper radiator is cold, then it simply means that your radiator is bad. You will need a complete overhaul or just replace your radiator with a new one.
Insufficient Air supply
Sufficient air is very important in keeping your engine in the right operating temperature. Otherwise, insufficient air supply will cause your engine to overheat especially in idle.
Why? Because your radiator (which is the main cooling component in cars) is an air-cooled device which depend on the amount of air entering the engine cabin.
Some may complain that their cars only overheats when in idle but the temperature goes back to normal when their cars are in motion.
This is because the radiator is either have a bad fan (fan clutch for rear-wheel/diesel vehicles), or the radiator fins are blocked by debris and dirt to the front of the raditor, or by having too much accessories like aftermarket horns, etc.
Radiators need maximum cooling and to accomplish that, it needs a functioning radiator fan and radiator fins that are free from debris. Of course, you also need to remove any accessories placed in your front grill to let the air outside to keep flowing inside the engine cabin.
This way, radiator tubes where it carries hot coolant, gets a sufficient flow of air from the fan and from the natural wind entering the front grill, which helps the coolant to have lower temperature before it flows back into the engine.
Bent or Damaged Radiator Fins
Aside from a radiator that is filled or blocked by debris that are stuck to the front of the radiator, airflow can also be blocked when most of the radiator fins are damaged or bent.
You can easily tell if your radiator has many bents or cracks by just looking at its physical appearance. If you see more bents or damage, then it will contribute to low or insufficient air flow which will lead to overheating.
But why does radiator fins gets damage? Does it naturally bend on its own? Well, not really! Here are some causes why radiator fins bend overtime.
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- Foreign objects hit them while driving in high speed
- Damage occurs when doing engine maintenance (fan removal, belt change, etc)
- Pressurized water hits the fins when washing the car
- Fins gets damage when the radiator is not installed carefully
So to prevent damaging radiator fins and any other fins in your engine bay like the turbo intercooler, avoid using pressurized water onto your radiator, use a metal mesh to protect your radiator from getting hit by debris on the road, and ask your mechanic to avoid damaging your radiator when doing engine maintenance.
Malfunctioning Heater
Another way to tell if you have a bad radiator is a malfunctioning heater. Cabin heater solely relies on the hot coolant that passes through the heater core. This allows hotter air to enter the cabin.
As mentioned above, a bad radiator will alter or halt the proper coolant flow inside the system due to clog or leaks. When this happens, you won’t get hotter air when you turn on the heater as hotter coolant doesn’t reach the core.
Most of the time, this is caused by a bad thermostat. However, a failing radiator can also cause this issue to occur. So better have these checked by a professional mechanic.
Summary
Radiator is a critical component not just to the cooling system itself, but to the whole engine. Without a functioning radiator, then you can never use your car to its fullest potential as it will certainly overheat.
So there you have it! If you see any of the signs above in your car, then chances are, you have a bad radiator! Have it replaced immediately by a professional mechanic or do it yourself. You can save more if you are the one working on your car.
Below is my video where I explain the internal parts of a radiator. You will learn a lot how radiator works in this video. It’s in Tagalog language but has English subtitle. Enjoy!
