TEST 2: Coolant Shooting Out From Open Radiator
The second most common end-result of a blown head gasket is engine compression pressures escaping into the engine's cooling system.
This can easily be verified by cranking the engine with the radiator cap removed (from the radiator). If one or both of the head gaskets are blown, then the coolant (inside the radiator) will be shot out forcefully.
If the coolant remains undisturbed, as you crank the engine, then you can move on to the next test.
IMPORTANT: Perform this test with a completely cold engine! If your 5.2L V8 Jeep Grand Cherokee has been running for any length of time, let it cool down completely before removing the radiator cap from the radiator!
Let's get started:
Remove the radiator cap.
Check to see if there is coolant in the radiator. If the radiator is empty then add some water or coolant to bring it up to the radiator's neck level.
Crank the engine with the help of helper, 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 out.
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.
Let's interpret your test result:
CASE 1: The coolant shot out from the radiator as you cranked the engine. This test result confirms that one or both head gaskets are blown on your 5.2L V8 Jeep Grand Cherokee.
The correct test result is for the coolant to remain undisturbed in the radiator as your Jeep Grand Cherokee's engine is cranked.
CASE 2: The coolant DID NOT bubble out NOR shoot out from the radiator. This is the correct and expected test result.
If the engine runs and does not overheat but runs with a misfire, your next test is a compression test. Go to: TEST 3: Engine Compression Test.
If the engine runs but overheats for no apparent reason, your next test is a block test with a block tester. For this test go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
TEST 3: Engine Compression Test
In some cases, one of the head gaskets gets blown (burned) at a point right between two adjacent cylinders (see the photo at the beginning of this tutorial for an example of this particular type of problem).
When this happens, you usually won't see the engine oil mixed with coolant or the coolant being shot out of the opened radiator.
The engine will start and run but those two side by side dead cylinders will cause the engine to misfire.
The best way to find out if this has happened is by doing a compression test.
These are the test steps:
Disable the ignition system by disconnecting the ignition coil from its electrical connector.
Remove all eight 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 as you observe the compression tester.
Have your helper stop cranking the engine once the needle on the gauge stops climbing.
On a piece of paper, write down the compression 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 cylinders.
Let's take a look at what your test results mean:
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.
If you still suspect a blown head gasket. Go to: 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.