Every engine depends on several key factors – It needs fuel to run, oil to keep everything lubricated, and coolant to prevent the whole system from overheating. That being said, engine cooling is a complex but often overlooked subject. As robust as engines can be, the cooling system is generally delicate. It’s incredibly easy to damage the radiator or spring a leak on one of the hoses. If you’re suspecting that your radiator is leaking, you can do a DIY radiator pressure test and find out. Likewise, you can also perform a complete cooling system pressure check. Here’s how.
Radiator Pressure Test
Pressure testing a radiator can be done using a homemade tester kit. For the radiator test, it’s best to remove the radiator from the car altogether. The effort of removing the fan, flushing the coolant, and removing the radiator is well worth it if you’re in a tight spot.
That being said, we’ll need a few things to build our tester:
- A new set of radiator hoses
- A piece of pipe to close the loop
- Two clamps
- A bike pump
- Radiator cap
- Set of stem valves
Bike Pump
Before we get into details, we just wanted to touch upon bike pumps for a moment. Although a bike pump is the heart of a DIY pressure tester, not all pumps are suitable for this job. You will need a quality pump with a gauge. If you don’t have a gauge, you can’t estimate the pressure in the system, which can cause all kinds of trouble in our second test (cooling system pressure test).
The quality of the bike pump matters as well. Cheap pumps will come with grossly inaccurate gauges. You don’t need surgical precision for this project, but you want to be somewhat accurate with your pressure readings, as creating too much pressure within the system can cause all kinds of damage. Alright, let’s get to testing the radiator.
Setting up the Test
First thing first, inspect the radiator for any apparent damage. You’re looking for any visible puncture holes made by rocks or your fan coming into contact with the radiator. If you can’t find any obvious damage, it’s time to put our pressure tester to use and check for leaks.
Step 1 – Mount Spare Hoses and Close the Loop
Remove the old hoses from the radiator and mount the spare set. We’re using spare hoses because they might get damaged in the process. We’ve mounted our spare set and used a piece of pipe (roll cage pipe in this case) to close the loop. Any kind of pipe will do as long as it allows you to form a positive seal using clamps. You need this to be airtight.
Step 2 – Mount the Bike Pump
In our particular case with this E30/E36 radiator. We’ve used the overflow outlet to attach our bike pump. Most other radiators have radiator caps. This is where you’ll need to do some DIY jerry-rigging for the tester to work.
Grab your new radiator cap, drill a hole in the center, and mount the bike stem valve to it. You’ll have to make sure that the stem valve is securely mounted on the cap and that it is forming a hermetic seal.
Once everything is set and your hoses are mounted to the radiator forming a closed loop, grab the bike pump and pump the system.
Step 3 – Reach Optimal System Pressure
Most radiators that come with a radiator cap will have the max system pressure rating etched or printed on the cap. That rating should be your red line. Don’t cross it. If you don’t have a cap, like us with this E30 custom aluminum radiator, you’ll need to consult your vehicle’s manual.
We’ve pushed this particular unit to 30 PSI, which is well above what standard factory BMW E30/E36 radiators are rated for. Most will be in the 15-18 PSI range.
Step 4 – Simulate Road Conditions
While the radiator is pressurized, inspect all hoses and clamps first. If everything is up to snuff, check the radiator for any air leaks. If there aren’t any, start applying force on the radiator to mimic road vibrations. Granted it holds, you can rest easy since your radiator is healthy.
Pressure Testing the Cooling System
If you’re suspecting that your cooling system has sprung a leak and your radiator is OK, you’ll need to pressure test the entire system. To do this, you’ll have to mount the radiator back on the car, run coolant through the system, and bleed air if your car requires manual bleeding.
Once everything is done, you’ll need that custom radiator cap you’ve made. Install it on the radiator and pump the system until you hit whatever the pressure rating is for your car. While the system is pressurized, start looking for leaks.
The first things you should be looking at are hose clamps. If your car has a few years under its belt, there’s a decent chance that your clamps have lost some tensions. This happens due to material fatigue but also due to constant road vibrations that are shaking the entire system.
If clamps are solid and your hoses aren’t leaking at the joints, start looking at the hoses themselves. Coolant hoses are known to become brittle over time because of the endless hot/cold temperature cycles. Given enough time and material fatigue, the hose will crack, causing either minor or major leaks in the system.
If your hoses are hard to the touch but aren’t leaking, you should consider a preemptive replacement of all cooling system hoses. Your choices for replacement vary from OEM cooling system hoses or aftermarket silicone ones. Either will work, although the latter won’t become brittle as they age.
What If You’ve Found No Leaks but the Pressure Keeps Dropping?
Performing the pressure test is usually an excellent way to tell if you have a leaky hose, a weak clamp, or similar issues with your cooling system. However, this test can also indicate much more serious issues, such as a blown head gasket. Some pressure loss is normal since your DIY radiator cap won’t be perfect, but any significant pressure leak could mean a bad head gasket.
If you pop open an average engine, you’ll notice several cooling ducts that run along the engine block. These ducts are often separated from the combustion chamber by a thin layer of engine block material. It’s not unusual to have head gaskets fail in these spots, which makes spotting the leak quite difficult.
Usually, your outer gasket perimeter will be intact, hiding any apparent signs of trouble. In case you’re losing pressure during the pressure test at home, and your hoses are solid, start checking the engine oil and coolant.
Some engines build more pressure in the lubrication system, causing the oil to end up in coolant. Others have higher pressure in the coolant system, which results in the terrifying milkshake engine oil. Check your overflow tank for oil in the coolant and your oil cap for any milky oil.
Get Quality Replacement Parts
If one or more parts of your cooling system are damaged, make sure to use quality OEM parts. Check out our catalog for Genuine OEM parts as well as quality aftermarket parts for your European car.
To find parts that match your car’s make and model, simply select it from the drop-down menu at our store. In case you have any questions regarding our offer, feel free to contact our customer support service.
A word of caution might be in order regarding the gauges on bicycle floor pumps. As a cyclist I have read a review of several brand-name floor pumps, which reported the pump gauges to be nearly always inaccurate.
Thanks Mark, that is a good point. This article assumes that you have a quality pump with a working gauge. The pressure numbers are also generalities, and in general you will be able to notice a leak well before you start crossing into any pressure numbers that may risk damaging a good radiator.
Good point. Here the key is to see that it holds pressure over time… Even if your gauge is off a good bit that’s ok, just make sure its not leaking! Note these are pressure tested at a MUCH higher rate at factory so we have a good margin UNLESS radiator is compromised.
Thanks for reading !
Months ago here in Lima Perú, in a Volvo repair service the´ve checked my radiator and cooling system using a hand made Pressure tester with a bicke pump, in whixch had included a Brake Booster Check Valve. The end of the hose was conected to a radiator fluid cup tank…. Worked wonderfull
Most important point is that it holds a pressure greater than operating pressure, not exactly what that pressure is…. Even if you are 20% high you should be fine as these rads are tested at a much higher rate before leaving factory…
Thanks for reading!