TEST 2: Coolant Shooting Out Of Radiator
As the engine turns, it's combustion cycle produces several different pressures (compression, combustion, exhaust, etc.). These gases/pressures are kept from entering the cooling system by the head gasket.
When the head gasket fails, it can no longer keep them sealed within the cylinder. Thus, they enter the cooling system thru' the cooling system passages in the cylinder head and block.
So, for our 2nd head gasket test, we'll check to see if the compression/exhaust pressure are trying to escape via the radiator.
These are the test steps:
- 1
Remove the radiator cap from the radiator. If the coolant level is low, top it off before proceeding.
IMPORTANT: The engine should be completely cold before you open the radiator cap. Opening the radiator cap on a hot engine can spray hot coolant all over you and severely burn you. - 2
Stand at a safe distance from the engine but within view of the radiator.
- 3
When ready, have your helper crank the engine.
You'll see one of two results: The coolant shoots out violently when the engine was cranked -OR- the coolant was not disturbed at all.
Let's take a look at what your test results mean:
CASE 1: The coolant shot out of the radiator. This confirms beyond a shadow of a doubt that you do have a blown head gasket on your hands.
CASE 2: The coolant DID NOT shoot out of the radiator. So far so good. In TEST 1, you confirmed that coolant isn't mixing with the engine oil. In this test you have confirmed that no exhaust gases are escaping thru' the radiator.
If you still think that you do have a blown head gasket on your Nissan, read the next test. Go to TEST 3.
TEST 3: Engine Compression Test
In a few instances, over the past few years, I have diagnosed vehicles with a blown head gasket that did not have coolant mixing with the oil and were not shooting the coolant out of the radiator when the engine was cranked.
Yet a blown head gasket they did have and the most important factor that all of these vehicles shared was that they had severely overheated.
OK, the test involves doing a compression test to see if two adjacent cylinders have 0 compression. I want to emphasize this, because this is important: Two adjacent cylinders will have 0 PSI compression.
This happens because the head gasket burns between two cylinders and thus the compression from one cylinder escapes into the other and vice versa.
- 1
Disable the fuel system and the ignition system.
- 2
Remove the spark plugs and install the compression tester (hand tight only) on the first cylinder you're gonna' test.
- 3
Have a helper crank the engine while you observe the compression tester. When the needle stops moving, have your helper stop cranking the engine.
- 4
Write down the compression readings. Repeat on the next 3 cylinders.
Let's take a look at what your test results mean:
CASE 1: You got 2 side by side (adjacent) cylinders with 0 PSI. This confirms beyond a shadow of a doubt that you do have a blown head gasket on your hands.
CASE 2: All cylinders had sufficient compression. After having done 3 tests, you have confirmed that you do not have a blown head gasket. But (and you know there's always one) if your vehicle is still overheating for no apparent reason, take a look at the next section: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
