‘Wet’ Engine Compression Test
If you've reached this point, you've found one or several cylinders with low or no compression. You might be wondering what's causing this compression test result. In this test section we're going to find out with a very simple and easy test.
This test involves adding about two tablespoons of engine oil to the cylinder that gave you a low or no compression test result in TEST 1. After adding the oil to the cylinder (with low or no compression), we're going to test its compression again.
Why add the engine oil? Because the engine oil will help to determine if the problem is in the piston rings, or if the problem is in the cylinder head valves.
OK, this is what you need to do:
Add a small amount of engine oil to the cylinder that reported low compression or no compression in the ‘Dry’ compression test.
- The amount should be about 1 to 2 tablespoons of oil.
Install the compression tester onto the cylinder.
- Do not use any type of tool to tightened the compression tester. Hand tight is fine.
When all is set up, have your helper crank the engine.
- You'll get one of two results, either the compression value will go up (from the one you recorded before) or it will stay the same.
Let's see what it all means:
CASE 1: The compression value shot up. This tells you that the piston compression rings are worn out and thus the problem is in the bottom end (block) of the engine in your 1.8L Mazda Protegé.
CASE 2: The compression value stayed the same. This confirms that the low compression problem of the affected cylinder is due to worn or damaged cylinder head valves.
Which Compression Tester Should I Buy?
There are lot of engine compression testers to choose from and many places to buy them. I'm gonna' make two recommendations to you:
1) Which one to buy: The engine compression tester that I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that it does not come with a case to store it in.
Engine Compression Gauge Testers
2) Where to buy: You can buy an engine compression tester just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!