How To: Find and Fix a Coolant Leak

Leaking coolant is getting more common as cars get older. Rubber ages and cracks, and from those cracks, leaks will form. If you run out of coolant and don't notice it, you can blow your head gasket and warp your engine's head casting, so tracking down leaks before they get out of control is important. Here's my guide on how to do it like a pro.

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Required Tools

• Mishimoto Radiator Pressure Tester Kit (With Vacuum Filler) OR
• Radiator Pressure Tester Kit (Without Vacuum Filler)

 

Note: I purchased the Mishimoto kit because I wanted a name brand behind my kit to make sure everything would work properly and fit. It also came with a vacuum fill attachment for the air compressor, which sucks all the air out of your coolant system when you're ready to fill it, and then very quickly sucks it out of the container. I wasn't as impressed with this part, so I also linked another cheaper kit if you don't have a compressor or don't want to try the vacuum filler. I haven't used the cheaper kit, but I'd guess it's identical in quality to the Mishimoto kit.

I'm going to cut to the chase: this job is incredibly hard without the right tool. I've chased leaks for so long, heating up the car and then rushing to open the hood and try to find where coolant is dripping. Even worse, I've had to try and figure out what's dripping on me and how many other things the coolant is dripping off of, creating false leads and hiding the true leak source.

Radiator Pressure Tester Pump

The right tool for the job is pretty simple. It's a "radiator pressure tester kit". It pressurizes the system to simulate the coolant heating up and expanding. 

It can be kind of hard to pump the manual pump over and over if the system is empty, so I usually go to the grocery store and buy 3 gallons of distilled water. It costs about $0.80 per gallon, and won't leave a mess on your driveway or make a mess on your car if you find a bigger leak. It does have to be distilled, or it can lead to impurities in your cooling system and cause damage or mineral buildup. If you already have coolant in your system, it's fine to do it with that as well, but just be prepared to clean up a little bit.

Steps

1. Fill the radiator with distilled water completely, until it won't take anymore. If you see your leak right now, that's great. If you're not exactly sure which hose or location it's coming from, keep reading.

Usually It's One of the Smaller 2 Radiator Cap Adapters

2. Choose the radiator cap adapter in the kit that fits your radiator securely. Once it's attached, connect the hand pump by pulling back the quick coupling and pushing it onto the radiator cap adapter.

This Picture Shows the Tester on a Coolant Overflow Tank; the RSX Just Uses the Radiator Cap Testing Location

3. You're going to be pumping until the pressure reaches between 16-17 PSI if you have a stock RSX radiator and cap. The stock RSX radiator cap is rated for 16 PSI, so this is as high as you need to go. I have a Mishimoto Racing Radiator and the cap for it is rated for 19 PSI, so I pump mine to 19-21 PSI. Just check your radiator cap for the rating and pump it up a tiny bit above it just to ensure it's leak-free.

Note: During this process, try not to move around the pump too much, or you'll accidentally let air out when you move the quick connect coupling. All the kits I've tried do this, and it's really annoying. Pumping does get hard and it can be a pain trying not to jiggle it around too much.

4. If there's a leak, you should get a spray of distilled water coming out of that location, which makes it a lot easier to find versus only the sound of rushing air and no visual aid. Replace the hose and spring clamps, or tighten your worm drive clamp in a different spot on the hose end, and see if the leak continues.

I wrote a guide that can help you figure out which hoses carry coolant and where to get a replacement for the hard-to-find discontinued parts as well. Check it out here. It can give you hints on where to check for leaks.

This has been a way I've figured out even the toughest leaks location within 15 minutes, every time. Once the leak area is patched up, test it again and see if it holds pressure and doesn't leak for a couple minutes. Just pump it up and come back in a few minutes and see what the pressure looks like.

Disclaimer:

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