The main thing you’ll be looking for is a gauge that covers at least 300PSI and ease of use. For the most part, they’ll be fairly accurate, and when you pick one out it’ll likely come down to convenience and how easy the gauge is to read to make your final decision.
Below are our reviews of the 4 best compression testers on the market, and afterwards, we go into what you should look for when selecting the right product.
INNOVA 3615 OHC Compression Tester Plus – 7 Piece Kit
This compression test kit from Innova is designed for hard to reach, recessed spark plugs. It comes with a lot of parts, but don’t let that fool you/ This one is all about convenience. It even has an 8” extension for especially hard to reach plugs. Add in a side valve which will allow you to depressurize the hose without having to remove it between cylinders and you know you’ll be in good hands when using this one.
OTC 5606 Compression Tester Kit
This kit from OTC can be trusted to a fault. It comes with all of the necessary qualities for a tester, as well as an extra-long hose which will make the whole process easy even for a novice. The quick couplings mean you can take care of the job even in an especially cramped engine compartment, and the 2.5-inch gauge is extremely durable. It’s a professional quality tool (see full specs), and it shows in the price, but it definitely won’t let you down. This is among the best compression testers period.
Lisle 20250 Compression Tester
The Lisle 20250 isn’t going to be the most advanced or prettiest product on this list, but the tool is sure to get the job done at the end of the day as long as your threads are either 14mm or 18mm. Sometimes a simple tool is all you need, and if you have easy to access plugs in the right size you could do a lot worse. The low price means it won’t break the bank and it’s really best suited for those who only own one vehicle that this will be able to easily access.
Mityvac MV5532 Digital Compression Test Kit
The Mityvac MV5532 is pretty much the best compression tester you’re going to find. The digital meter is extremely accurate and the kit comes with everything necessary to hit the plugs in nearly any gasoline motor that you can bring it to. There’s a ton of hoses and different adapters, it’s durable, and it’s extremely simple to use at the end of the day. The price reflects it, but you’re simply not going to be able to do any better.
Picking Your Compression Tester
Which one of the above options you decide to go with will largely depend on your uses. If you have a shop, or if you’re even the type of guy that everyone comes to when there’s automotive trouble afoot, then one of the test kits which can handle a wide range of different plugs but if it’s just your car then you can get away with a cheaper option.
We do recommend the Mityvac (see full specs) for nearly anyone. The simple usage and easy to read meter make it a superior tester for almost any application.
When you’re using an analogue gauge and trying to get accurate measurements, there’s one main thing to look out for which is parallax. With any analogue gauge, parallax will occur when you aren’t looking dead on at the gauge, causing the reading to seem higher or lower depending on the angle of viewing. Most people will instinctively look them dead on, but it’s important to keep track of as the variance in your readings can be quite large from seemingly small angles.
Using Your Compression Tester
Using one is simple, pretty much anyone who knows their way around a tool box should be able to do it.
Begin by removing the spark plugs from your engine and setting them to the side, then disconnect the fuel pump. Make sure you do the latter, as you only want to test the compression and not dump fuel into the engine itself, without the spark plugs it’s not going to ignite.
After you do this crank the engine four or five times. This will achieve compression and allow you to make sure that you have the proper reading. If you don’t have a constant PSI reading at this point you can allow the engine to crank up to ten times, but remember to keep doing it with all of the cylinders so you have equal readings.
It’s recommended to mark each cylinder’s pressure down as you go so that you can diagnose the problem afterwards. A piece of chalk will let you easily write on most engines.
Your PSI should read at over one hundred in each of the cylinders if your engine is healthy. Some models will read higher, but none will be reading lower. Look it up if you have a specialized motor, but the 100 PSI mark is a good indicator.
After you do this, you can further diagnose the problem pretty easily. Add a teaspoon of engine oil to the cylinder and take another compression reading. If your pressure jumps up after you do it then your piston rings are worn, if it doesn’t then you’ve got valve problems.
As you can see, getting the best compression tester is one of the smartest things you do for your car and garage. Anyone can do it and the reading itself is likely to cost more than the kit if you have to take it into a shop. Grab the best one you can afford, and start getting your diagnosis right in your garage. It’s hard to regret being able to know exactly what’s going on with your vehicle.