TEST 2: Compression Shooting Out Of The Radiator
Another of the most common symptoms of a blown head gasket is the engine's compression or combustion gases entering the cooling system and shooting out of the radiator (if you open the cap and crank the engine).
This happens when your 2.4L Nissan Altima (Frontier or Xterra) overheats to the point where the cylinder head warps and/or the head gasket burns in several spots.
Now, usually when this happens (combustion gases/pressures shooting out of an open radiator), your 2.4L Nissan Altima (Frontier or Xterra) won't start. More to the point, it will Crank but Not Start.
IMPORTANT: If your 2.4L Nissan Altima (or Xterra, Frontier) does Start and has been running for an extended amount of time, let the engine cool down for at least an hour, since this test step will ask you to remove the radiator cap. Be careful and remember that a radiator cap should never be removed from a hot radiator.
But if you Nissan Frontier (Altima or Xterra) doesn't start, you obviously don't have to worry about hot coolant from a hot engine.
OK, let's get started:
Remove the radiator's cap from your Nissan's radiator.
Check the coolant level in the radiator. If the radiator is empty, add some water or coolant to bring it up to the radiator's neck level.
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.
Why? Well, because if the head were not warped and/or the head gasket not blown, then cranking the engine should have no effect whatsoever on the coolant inside the radiator.
So, when you have coolant shooting out of an open radiator., this 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, this is normal.
If you were to ask 10 persons, what is the most common symptoms of a blown head gasket, 9 out 10 would say: 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.
But, this isn't always the case. I have diagnosed and repaired blown head gaskets where these two symptoms were not present.
What did nail down the head gasket problem was an engine compression test or a block test. If the engine doesn't start, go to: TEST 3: Compression Test.
If the engine starts, but overheats, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
TEST 3: Compression Test
What leads a lot of folks to misdiagnose a blown head gasket on their 2.4L Nissan Frontier (Altima or Xterra), is that they pulled out the engine oil dipstick and saw that the engine oil WASN'T mixed with coolant. In other words, the oil was not a milky white color (as will happen in the majority of blown head gasket cases).
They also did the ‘crank the engine with radiator cap off of the radiator’ test and the engine's compression or combustion gases were not violently shooting out from the radiator's filler neck.
They never realized that a head gasket can get blown without causing the coolant to mix with the engine oil and without causing combustion gases from entering the cooling system. I have seen this enough to know that one more test has to be done.
How is this possible? Well, this happens because 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 to leak into the other and vice-versa, but nothing else (like coolant).
If this has happened to your 2.4L Nissan Altima (or Xterra, Frontier), then more likely than not your Nissan cranks but won't start.
This condition can be very easily verified by doing a compression test. In this test step I'll show you how and more importantly, how to interpret the compression test results to see if the head gasket is burned or not. This is what you'll do:
Disable the ignition system so that spark won't be created and delivered to the spark plug wires.
Nissan with a distributor ignition system: Disabling the ignition system is done by disconnecting the ignition coil's connector (if the ignition coil is located outside of the distributor on your Nissan). If your Nissan vehicle has the ignition coil inside the distributor, disconnect the distributor's connectors, and this will disable the ignition coil.
Coil-On-Plug (COP) ignition system: You don't have to worry about disabling the ignition system here, because you have to remove all four COP coils and this will effectively disable the ignition system.
Disconnect all four spark plug wires (if your Nissan is equipped with a distributor) or remove all 4 COP coils (if your Nissan is equipped with COP coils).
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.
Once the tester's needle 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 illustration above to help you identify the cylinder).
Repeat steps 4 thru 7 on the remaining 3 cylinders.
Let's analyze your test results:
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.
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.