HEAD GASKET TEST 2: Coolant Shooting Out From Open Radiator
The second test, that you'll perform on your Nissan Sentra, is to see if the engine's compression or combustion gases are entering the cooling system.
When this happens, you'll have coolant shooting out violently from the radiator (with the radiator cap removed of course).
IMPORTANT: If your Nissan Sentra starts and runs and it has been running for an extended amount of time, let the engine cool down for at least an hour, since this test step requires that you remove the radiator cap. Be careful and remember that a radiator cap should never be removed from a hot radiator.
There's a good chance that your 1.8L Nissan Sentra is not starting, in this case you don't have to worry about a hot engine.
Remove the radiator's cap. Check to see if there is coolant in the radiator. If the radiator is empty, add some water or coolant to bring it up to the radiator's neck level.
Now, have a helper crank the engine, while you stand at a safe distance from the open radiator.
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 will not be disturbed. In other words, cranking the engine will have no effect on the level of the water or coolant 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 happens when the head gasket has blown and/or the cylinder head has warped due to the 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 level of the coolant in the open radiator, then so far so good, since this is the normal result.
If you were to ask 10 persons, what is the most common symptom of a blown head gasket, 9 out 10 would say, without hesitation, engine oil mixing with coolant and engine compression/combustion gases shooting out of an open radiator neck and yes they would be right but not in all of the cases. There are times when this doesn't happen and so the next test will help to further verify this, go to: HEAD GASKET TEST 3: Engine Compression Test.
HEAD GASKET TEST 3: Engine Compression Test
There are times that when the head gasket gets blown, it just burns between two cylinders.
When this happens, you usually don't see engine oil mixed with coolant and you don't see the coolant being pushed out of radiator (with it open and with the engine cranking). I have seen this enough to know that one more test has to be done.
To explain this a little further: When the head gasket has burned at a point between two cylinders, the resulting gap in the head gasket will let only the compression/combustion of one cylinder leak into the other and vice-versa, but nothing else (like coolant). If this happens, in a Nissan Sentra, this will cause a no start condition.
In this test step I'll show you how to test the engine compression and more importantly, how to interpret the results to see if the head gasket is burned or not.
This is what you'll do:
The ignition system must be disabled so that spark won't be created and delivered to the spark plug wires.
Distributor type ignition system: You can do this by disconnecting the ignition coil's connector, if the ignition coil is located outside of the distributor on your Nissan. If your Nissan Sentra has the ignition coil inside the distributor, disconnect the distributor's connectors, and this will disable the ignition coil.
COP ignition coil system: Removing all 4 COP ignition coils will disable the ignition system.
Remove all four spark plug wires and then remove all of the spark plugs.
Thread in the compression tester by hand, on the first spark plug hole you're gonna' start with.
Do not use any tools to tighten the compression tester. Hand tightening the compression tester is more than enough to get the proper results.
Have a helper crank the engine while you keep your eyes on the compression tester. The needle will climb, as the engine cranks, till it reaches the maximum cylinder compression. At the point it stops climbing, have your helper stop cranking the engine.
On a piece of paper, write down the reading and what cylinder it belongs to (you can use the image in the image viewer to help you identify the cylinder). Repeat the above steps in the remaining 3 cylinders.
If your Nissan Sentra's head gasket is burned at a location between 2 cylinders, your compression test readings will give you 2 good compression readings and 2 compression readings that will be 0 PSI. Let me give you a more specific example:
Let's say that I tested my Nissan Sentra and I got the following cylinder compression readings:
- Cylinder #1 = 175 PSI
- Cylinder #2 = 165 PSI
- Cylinder #3 = 0 PSI
- Cylinder #4 = 0 PSI
As you can see from the above compression readings, cylinders #3 and #4 have 0 PSI readings. And this is a clear indication that the head gasket has burned at the point between them both. Now, in your specific case, you may not see those exact same cylinders with 0 PSI readings. It may be #1 and #2 or it may be #2 and #3, the main idea is that whatever cylinders are affected, they will always be side by side.
CASE 1: All cylinder compression readings where normal. These compression gauge readings confirm that the head gasket is OK and not burned at a point between two cylinders.
Your next test doing a block test. For this test go to: HEAD GASKET TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
CASE 2: Two side by side cylinders had 0 PSI compression. This engine compression reading confirms that the head gasket is burned thru' at the point between those two cylinders. You will need to replace the head gasket.