What to do After Installing New Radiator?-The Ultimate Guide

Installing a new radiator improves the engine’s cooling system, preventing overheating damage and compromising the transmission. The replacement process can sometimes be intricate, especially if it’s your first time doing it. Besides, doing it while the radiator is full of a coolant can be tricky. But once you do, it’s prudent to ensure the radiator is well intact and functioning optimally. This article explains what to do after installing a new radiator on your vehicle.

What to Do After Replacing a Radiator?

During the removal of the damaged radiator and installation of the new one, the engine loses lots of oil and transmission fluid. This needs to be replaced. Besides the oil, you also need a large amount of new coolant. As aforementioned, the coolant helps to trap excess heat generated by the running engine. So once you attach the hoses, bolts, and piping to the new radiator, add the new coolant. 

Start by removing the reservoir cap and adding the correct coolant to the reservoir, not the radiator itself. You have the option of using diluted coolant itself or repairing a 50/50 mixture of concentrated coolant and distilled water. Remember, you should only add the coolant when the engine is off. Adding the coolant when the engine is running could result in severe burns. Also, you cannot tell the correct level of the coolant when the engine is running. 

You need to examine the overflow tank and add the coolant until the level reaches the service line. Once you finish adding the coolant, start your car and allow the engine to run for several minutes. While the engine is running, check for leaks. If no leaks are present, you did a good job, and you don’t have to repeat this process again for the next 100,000 miles. 

To top off the coolant, shut off the engine and then add a little more water and antifreeze until it starts to appear in the bottom of the overflow tank. Open the overflow tank cap, then top it off with distilled water and antifreeze. Stop a couple of inches just below the service line. Now, you’re done. 

Remember to check the oil and transmission fluid levels before and after the installation of the new radiator. 

Check if the Radiator Drain Petcock is Closed

When installing the radiator, it’s pretty easy to spot fault on the petcock when coolant-full. But mostly, it becomes much easier replacing the radiator when it’s empty and refilling it later when you’re done. Tinier vehicles won’t make it challenging to replace old radiators, but heavier ones require doing while the radiator is empty. And that prompts a quick check after installing it.

The radiator drain petcock located at the bottom helps ameliorate the draining process without requiring you to disengage the radiator entirely. Besides, it prevents the coolant from leaking through the slot at the bottom. A leaking radiator drain petcock can give you a run for your money trying to refill your coolant if you hardly notice it.

Check If You Have the Right Coolant

The modern automotive industry manufactures automobile cooling systems with parts made from aluminum, steel, copper, steel, and silicon alloys. That means radiators aren’t compatible with a single coolant like back when cooling systems were mostly cast iron, brass and rubber parts. You need to consider numerous factors, including your vehicle’s model, the make, engine, and year.

The glad tiding is that you have a few coolant choices, and you should understand which works best for you. The Inorganic Additive Technology (IAT) coolant is suitable in modern cars but requires frequent changing. However, the Hybrid Organic Acid Technology (HOAT) coolant is usually the best since it doesn’t require frequent changing.

Dilute Your Coolant with Distilled Water

Before adding your coolant to the radiator, dilute it with distilled water. Pre-mixed coolants are inarguably cheaper and usually won’t give you difficulty figuring out the best ratios to use. It’s also prudent to use distilled since there are good reasons why manufacturers don’t recommend regular tap water. Distilled water is usually devoid of minerals that might form some deposits inside the radiator. That can, in the long run, make it inefficient.

You can use a 50/50 ratio to mix your coolant with water. However, you might have to vary the ratios a bit during extreme winters, with the coolant being larger in proportions. Besides, some coolants have specific ratios you can use to mix with water. So, be sure to read the owner’s manual for some clarity.

Open the Valves

Once you have your cooler mixed with distilled water, pour it into your radiator until Full. Then, ensure that the caps and valves are open enough, probably by making the same number of turns as you closed them. That should prepare you to bleed the radiator, later on, to get rid of trapped air. Bleed the Air from the Cooling System. Bleeding helps get rid of trapped air in your cooling system.

Air in your radiator reduces its working efficiency, and while it may not necessarily damage it, it won’t work as optimally as it should. Besides, trapped air uses a lot more energy than the standard rates, which can strain your vehicle’s electrical system. You can use the radiator bleed key and let the coolant run a few drops down.

But how do you properly bleed your radiator?

Ensure that the heating system is off before turning the radiator key. If you’ve revved the engines for a while, you might be hit by hot spouts when the water sprays. And while turning the key, be keen to catch some hissing sounds to signal the air escaping. Once the hissing stops, retighten the valves by counter-turning the radiator key.

Turn the Central Heating Back On

Turn the central heating back on when the bleeding is successful, and the valves are shut. You can check the pressure at the gauge on the boiler to ensure that the radiator is working as it should. Perhaps, you could rev the engines for some time to ensure that your installation is successful.

How Do I Check the Transmission Fluid and Oil Levels?

To check the transmission fluid level, locate the dipstick in the engine compartment. Make sure you’re locating the transmission oil dipstick, not the engine oil dipstick. You can find the transmission dipstick further back in the engine bay toward the firewall. It’s usually marked with a transmission symbol or color. 

With the engine warmed up, pull out the dipstick, wipe it clean, replace it, then pull it back out. Check the fluid level against the full, fill, and low marks. If the transmission oil level is low, top it off. This is usually done through the same tube where the dipstick fits. To add transmission fluid, use a funnel with a narrow spout. To check the oil level, look for a dipstick with a small colored handle. It could be orange or yellow with an oil can symbol.

Just like the transmission dipstick, pull the oil dipstick, wipe any oil off, then re-insert it slowly. Withdraw the dipstick and look closely at the tip. If the oil is between the two lines, your vehicle has enough oil. But if it’s at the low mark or below, add a quart.

Why Does My New Radiator?

If you hear water trickling or dripping inside your new radiator, that means it contains air pockets inside. This is common and often occurs when you fill them too quickly. This causes air to be trapped within the radiator. The best way to fill a radiator is to open up the valves then fill the radiator and finally, bleed it to make sure no air remains within the radiator. Running your engine also helps to remove any air bubbles in the system. Simply run the engine with the radiator cap off. This will allow the air bubbles inside the system to escape. 

Do I Need to Flush a New Radiator? 

The radiator coolant is very important to the running of your engine. However, it builds up unwanted debris and contaminants. Over time, it can cause radiator corrosion. This generates rust, and it’s something you don’t want for your car engine. To only way to resolve such a problem is through a full flush. A flush involves the use of several gallons of distilled water and forcing it through the system to get rid of the old antifreeze and contaminants.

Besides removing the old antifreeze, a full flush will lubricate and lengthen the life of your water pump. The best way to drain your radiator is to remove the cap, open the petcock valve or remove the bottom radiator hose. This will allow you to drain the coolant into a plastic reservoir. When you install a new radiator, you don’t have to carry out a full flush.

However, car manufacturers recommend that you carry out a radiator flush after 10,000 miles. If there are no signs that you need a radiator flush you can do it after 30,000 miles. Alternatively, check your owner’s manual. If you take your vehicle to a mechanic for a radiator full flush, always make sure the mechanic performs a full cooling system inspection. This will help to reveal any leaks in the system. If any, the mechanic will fix them. If the mechanic flushes the system and ignores the leaks, your engine will overheat.


Having a working radiator is the key to a long-lasting engine. And right after installing it, you must ensure your post-installation procedure is well done. Be sure to work with the right coolant and read through the owner’s manual exhaustively. Since not all post-installation procedures are similar, you might find your manufacturer’s two cents helpful.

3 thoughts on “What to do After Installing New Radiator?-The Ultimate Guide”

  1. Thank you very much for the information about my radiator I had a new radiator put in my car and Amante Kia and August the 2022 my main question is they claim that they didn’t replace the hoses and now I’m having trouble with my temperature gauge going up and down and the Heat and air in the car working. The mechanics are saying that they didn’t replace the hoses when installing a new radiator and now they want to charge me over $700 to do the work!


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