TEST 2: Coolant Shooting Out From Open Radiator
The second test you'll perform on your Nissan Sentra is to determine if the engine's compression or combustion gases are entering the cooling system.
When engine compression/combustion gases enter the cooling system, coolant will spurt violently out of the radiator (with the radiator cap removed).
IMPORTANT: If your Nissan Sentra starts and runs and it has been running for an extended amount of time, allow the engine to cool for at least an hour, as this test step requires you remove the radiator cap. Be careful and remember that a radiator cap should never be removed from a hot radiator.
If your 1.8L Nissan Sentra does not start, you don't have to worry about a hot engine.
- 1
Remove the radiator cap.
- 2
Check if there is coolant in the radiator. If the radiator is empty, add some water or coolant.
- 3
Now, have a helper crank the engine, while you stand at a safe distance from the open radiator.
- 4
You'll see one of two results:
1.) The water or coolant inside the radiator will shoot up and out of the now open radiator.
2.) The coolant is not disturbed. In other words, cranking the engine has no effect on the water or coolant level in the radiator.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: The coolant bubbled out or shot out from the radiator. This is a clear indication that the head gasket is blown.
This test result only occurs if the head gasket has blown and/or the cylinder head has warped due to engine overheating. No further testing is required.
CASE 2: The coolant DID NOT bubble out NOR shoot out from the radiator. If cranking the engine had no visible effect on the coolant level in the open radiator, then so far so good as that is the normal result.
If the engine doesn't start, go to: TEST 3: Engine Compression Test.
If the engine runs, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
TEST 3: Engine Compression Test
Sometimes the head gasket simply burns between two cylinders when it fails.
When this happens, you typically don't see engine oil mixed with coolant, and you don't see coolant being pushed out of the radiator (with it open and the engine cranking).
To explain this a little further, when the head gasket is burned at one point between two cylinders, the resulting gap in the head gasket allows compression/combustion of one cylinder into the other and vice versa, but nothing else (like coolant).
If your Nissan Sentra's head gasket is burned anywhere between 2 cylinders, those cylinders will not produce compression and the engine will crank but not start.
In this test step, I'll show you how to test engine compression and more importantly how to interpret the results to determine if the head gasket is burned or not.
This is what you'll do:
- 1
Remove all 4 COP ignition coils.
- 2
Remove all four spark plugs.
- 3
Thread in the compression tester by hand on the first spark plug hole you're gonna' start with.
NOTE: Do not use tools to tighten the compression tester. Tightening the compression tester by hand is more than enough to get the right test results. - 4
Have a helper crank the engine while you keep an eye on the compression tester.
- 5
Have your assistant stop cranking the engine at the point where the needle on the gauge stops rising.
- 6
Write down the compression reading and which cylinder it belongs to (you can use the illustration above to identify the cylinder).
- 7
Repeat the steps 3 to 6 on the remaining 3 cylinders.
Let's examine what your test results mean:
CASE 1: All cylinder compression readings where normal. This test result confirms that the head gasket is OK and not burned at a point between two cylinders.
Your next test is doing a block test. For this test go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
CASE 2: Two side by side cylinders had 0 PSI compression. This test result confirms that the head gasket has blown at the point between these two cylinders. You need to replace the head gasket.
