High Pressure in Coolant System When Cold: Check for These 5 Causes (And How to Fix It)!

Published:

Updated:

Author:

High Pressure in Coolant System When Cold

Disclaimer

As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.

From physics, you may recall that temperature and pressure have a linear relationship. As temperature lowers, the pressure too goes down. Hence, common sense dictates that a cold car shouldn’t have pressure in the coolant system when cold.

But what causes pressure in the coolant system when cold? One possible cause is that your car isn’t really cold. It takes time to dissipate heat from the engine. Other causes include air and exhaust gasses in the coolant system. A bad radiator seal and blockage in the system also cause this phenomenon.

In this article, I’ll draw on my years of experience to explain the science in simple terms and walk you through the solutions.

High Pressure in Coolant System When Cold

Causes of Pressure in Coolant System When Cold

Here are the culprits behind your coolant system having pressure when you know the car is cold.

1. Residue Heat

From experience, I’ve found out cars take hours to become completely cold. Yes, your car’s exterior might feel cold, but interior parts could be hot. Since there is coolant in those parts, it will also be hot, resulting in the pressure.

You will know residue heat is the causative if:

  • You were on a long-distance trip, and you never allowed enough time for cooling.
  • The engine is still warm when you touch it.

2. Air in the Cooling System

Inadequate maintenance, like not bleeding the cooling system during coolant replacement, introduces air pockets. Air pockets obstruct the flow of coolant. The pockets prevent coolant from effectively transferring heat through the system. So, you will have part of your coolant hot, even though the car is cold.

Signs of air in the coolant include:

  • Bubbling and gurgling noise as the coolant circulates
  • Fluctuating temperature gauge readings

3. Exhaust Gasses in the System

Problems with the cylinder head or head gasket can cause exhaust gasses to escape into coolant passages. The introduction of exhaust gasses into the coolant leads to pressure changes. It comes with the following signs:

4. Bad Radiator Cap

The radiator also doubles as a pressure regulator. When there are gasses or excess coolant, it allows them to flow into the expansion tank or overflow. When it is malfunctioning, it can’t undertake its job well, leading to high pressure.

Signs of a bad radiator cap include:

  • Visible damage like signs of wear and deterioration.
  • Bulging radiator cap due to excess pressure.

5. Coolant System Blockages

Dirt in the coolant reservoir restricts the flow, causing it to accumulate in specific areas. In those areas, it will be hot and pressurized.

Signs of blockages are:

  • Engine overheating when in operation
  • Debris and particles in the radiator

Does Pressure in the Coolant System When Cold Spell Disaster?

Does Pressure in the Coolant System When Cold Spell Disaster?

No. However, you shouldn’t ignore the sign as it indicates a problem with the cooling system. If left unchecked, it will escalate into major issues and hefty repair bills.

The consequences of ignoring this issue are:

  • Overheating: This will, in turn, cause severe damage to your internal combustion engine parts.
  • Leak development: Since you have excessive pressure, gaskets and hoses will be strained. This would lead to pipe bursts.

How to Troubleshoot Pressure in a Coolant System When Cold

Here are the steps I would follow when troubleshooting this problem:

1. Double-check your Engine and Ambient Temperature

The time it takes for the engine to cool down is about 2 to 6 hours. This depends on the engine size, vehicle type, weather conditions, and so on. Touch the engine block or cylinder head to feel the temperature and ascertain it’s actually cool.

2. Inspect and Replace the Damaged Radiator Cap

Follow these steps to learn how to replace the damaged radiator cap:

  • Ensure the engine is cold before proceeding.
  • Identify and open the radiator cap. It is on top of the radiator or in the overflow reservoir, depending on your car module. To remove the cap, press down and turn it counterclockwise.
  • Inspect this cap for cracks, corrosion, or damaged gasket.
  • Replace if damaged. Buy a new cap for $11 to $34. Turn it clockwise until it clicks in place when installing.

3. Bleed the Cooling System to Remove Air

If you have signs of air in the coolant mentioned in the above section, you need to bleed the system to remove that air. Follow these steps:

  • Mix your antifreeze with distilled water 50/50. You can also buy one that is pre-mixed. (We recommend the Vapor Distilled Premium Water. It comes deionized and demineralized, so you don’t have to worry about impurities in your coolant.)
  • Open your radiator and top it up till it’s full.
  • Start your vehicle.
  • Set the AC to the highest possible heat. Set the fan to the lowest possible heat.
  • Let the vehicle run for several minutes while you monitor the air temperature coming out of your vents.
  • Top up the radiator with more coolant till it’s full.
  • Let it run for several minutes, and then top it up again. Close the radiator.
  • Take your car for a road trip. Once back, top up the radiator for the last time.

Here is a YouTube video to illustrate the above steps visually:

4. Check your Exhaust Emissions

While the engine is running, test coolant for exhaust gasses. Normal emissions are transparent and slightly whitish due to water vapor.

If you have white smoke with a sweet odor, follow these steps:

  • Ensure the engine is cold before starting.
  • Drain all the coolant. There is a radiator cap under your car on the driver’s side. Open it and collect all the coolant. Dispose of it properly in your sewer system and not on the ground.
  • Remove the cylinder head to assess the damage. Check the pipes that are corroded, damaged, and have holes. Replace those pipes with new ones of the same type.
  • Also, check your gaskets and seals and replace all that have signs of damage and tear.
  • Reassemble the engine, but do not refill the coolant yet, as you’ll need to flush the system.

5. Flush the Coolant System to Clear the Blockage

Use the steps below to flush out debris and impurities in the coolant pipes and components:

  • Close the drain cap and fill the radiator with distilled water. Please note that it is distilled water and not filtered water.
  • Start the engine. Give it a few minutes till the engine heats up and the coolant begins to circulate.
  • Add more distilled water.
  • Pour in a flush fluid. It costs $5 to $15, depending on the brand.
  • Go for a road trip. Drive around for 10 to 20 minutes for the solution to circulate around your cooling system.
  • Wait for the engine to cool down and drain the distilled water as you did in step 4.
  • To ensure everything is drained, start your engine and give it some gas.
  • The water should be clear. Install the radiator drain cap.
  • Add your 50/50 coolant.

Here is a YouTube video to guide you visually:

Conclusion

While pressure in the coolant system when cold, might seem like an ominous warning sign. Understating the root causes puts you in the driver’s seat. With the knowledge and a methodical approach, you will properly diagnose and repair.

Don’t forget to keep up with your maintenance routine for the coolant system. You can also use an anti-rust solution for added protection. Your engine will thank you!

About the author

Leave a Reply

Your email address will not be published. Required fields are marked *