How To Test For A Blown Head Gasket (1999-2007 4.7L V8 Jeep Grand Cherokee)

In this tutorial, I'll walk you through the four most common ways to check for a blown head gasket on a 1999–2007 4.7L V8 Jeep Grand Cherokee.

Each of these tests is straightforward and will help you either confirm or rule out a head gasket problem with confidence.

Two of the checks can be done in just a few minutes and don't require any special tools. The third involves doing a standard compression test (you'll need a compression gauge for this one). The fourth test uses a combustion leak detector, also known as a block tester. Before jumping in, I recommend reading through the whole guide so you'll know exactly which test to start with and what to expect.

You can find this tutorial in Spanish here: Cómo Probar Un Empaque De Cabeza Quemado (4.0L Jeep) (at: autotecnico-online.com).

Symptoms Of A Blown Head Gasket

On the 4.7L V8 Jeep Grand Cherokee, the head gasket usually fails after the engine has overheated. Overheating can be caused by a bad radiator fan or fan clutch, a stuck thermostat, or a coolant leak that leaves the system running dry. Once the gasket blows, here are the most common symptoms you'll see:

1. Overheating: The engine continues to overheat, even after ruling out the fan, thermostat, or a low coolant condition.
2. White smoke: Thick white smoke pours out of the tailpipe. It usually has a sweet smell, like hot antifreeze being burned inside the cylinders.
3. No-start condition: The engine cranks but won't start. You've already confirmed you have spark, and you know the fuel system is working, so lack of compression from a blown gasket is the likely cause.
4. Oil contaminated with coolant: The engine oil looks milky or frothy, with a tan or off-white color from coolant mixing with it.

TEST 1: Engine Oil Mixed With Coolant

One of the classic signs of a blown head gasket on the 4.7L V8 Grand Cherokee is coolant mixing with the engine oil. This first test will help you check for it quickly.

Here's what to do:

1. 1

   Open the hood on your 4.7L Jeep Grand Cherokee.

2. 2

   Pull out the engine oil dipstick and wipe it clean.

3. 3

   Check the oil's appearance:
   
   1.) If the oil looks like coffee with way too much cream (a milky tan/off-white color), coolant is mixing with the oil.
   
   2.) If the oil looks normal (dark brown to black, depending on age), no coolant is present in the oil at this point.

Now, here's what the dipstick results mean:

CASE 1: The oil looks milky and thick. This confirms coolant contamination and a blown head gasket on your 4.7L Grand Cherokee. You can stop here —no further testing is needed.

Why the oil looks this way:

1.) The engine overheated badly enough to warp the cylinder head, which in turn damaged the head gasket.
2.) Once the gasket fails, it can no longer keep combustion gases, oil, and coolant separated.
3.) Coolant leaks into the oil pan and mixes with the oil, producing the thick, frothy tan color you see on the dipstick.

CASE 2: The oil looks normal. That's a good sign so far, but it doesn't completely rule out a blown head gasket. Continue to: TEST 2: Coolant Shooting Out Of Open Radiator.

Here's why: Although oil contamination is common when a head gasket blows, it doesn't always happen. Your 4.7L Grand Cherokee could still have a blown head gasket even if the dipstick looks fine. That's why additional tests are needed to get a solid confirmation.

TEST 2: Coolant Shooting Out Of Open Radiator

The next test you can do to confirm a blown head gasket on your 4.7L V8 Jeep Grand Cherokee is to remove the radiator cap and crank (or start) the engine. What you're checking for here is whether cylinder compression is leaking into the cooling system.

Important safety reminder: Never remove the radiator cap while the engine is hot. If your Jeep has been running, let it cool down for at least an hour before performing this test. If it's not starting, then the coolant will already be cold, so you won't have to wait.

Here's how to do it step by step:

1. 1

   Remove the radiator cap.
   
   If the radiator is low or empty, add plain water until it's full (for this test, water alone is fine —no need for coolant).

2. 2

   Have a helper crank the engine while you watch the open radiator neck from a safe distance.

3. 3

   Pay close attention to what happens:
   
   1.) The coolant will bubble up violently or shoot out of the radiator opening.
   
   2.) The coolant will remain calm and undisturbed. Cranking the engine will not change the level inside the radiator.

Now let's interpret the results:

CASE 1: Coolant shoots out or bubbles up from the radiator. This is a sure sign of a blown head gasket on your 4.7L V8 Grand Cherokee. What's happening is that the combustion gases from one or more cylinders are escaping into the cooling system, pressurizing it and forcing the coolant out. At this point, no further testing is really necessary.

CASE 2: Coolant level stays steady. If there's no bubbling or shooting coolant, that's a good sign so far. But don't cross the head gasket off the list just yet —some failures don't show up in this test. Your next step depends on what the engine is doing:

• If the engine starts but runs with a misfire, move on to: TEST 3: Engine Compression Test.
• If the engine runs but overheats quickly for no obvious reason, move on to: TEST 4: Using A Block Tester (Chemical Combustion Leak Tester).

TEST 3: Engine Compression Test

Sometimes the head gasket fails right between two neighboring cylinders, creating a gap that lets one cylinder's compression leak into the other and vice versa. When this happens on a 4.7L V8 Jeep Grand Cherokee, it usually causes a rough misfire or even a no-start condition depending on how bad the leak is.

The best way to confirm this is with a compression test. In this section, I'll show you how to do it, and just as importantly, how to read the results so you'll know if the head gasket is blown.

NOTE: You can find a complete step-by-step explanation of this test and how to fully interpret the results here: How To Test Engine Compression (1999-2007 4.7L V8 Jeep Grand Cherokee).

This is what you'll need to do:

1. 1

   Disable the ignition system. On the 4.7L, this means disconnecting all eight Coil-On-Plug ignition coils. This prevents spark during the test.

2. 2

   Disable the fuel system. The easiest way is to remove the ASD (Auto Shut Down) relay or unplug all eight fuel injectors.

3. 3

   Remove all eight spark plugs.
   
   Be sure to keep track of which plug came from which cylinder. This will also give you a chance to inspect them for signs of coolant contamination (white crusty deposits) while you're at it.

4. 4

   Thread in the compression tester into the first cylinder you're going to test.

5. 5

   Have a helper crank the engine while you watch the tester's gauge.

6. 6

   When the needle stops climbing, have your helper stop cranking the engine.

7. 7

   Write down the reading and note which cylinder it belongs to.

8. 8

   Repeat the process for the remaining seven cylinders.

Here's how to interpret your results:

CASE 1: All eight compression readings are within spec and fairly even. This tells you the head gasket is not blown between cylinders.

If all three of the previous tests still point to the head gasket being OK but your Jeep continues to overheat and you strongly suspect gasket failure, then move on to the last check: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

CASE 2: Two side-by-side cylinders have 0 PSI compression. This confirms that the head gasket is burned through between those two cylinders and is no longer sealing compression.

TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)

Sometimes a blown head gasket can be tricky to pin down. If the first three tests haven't been able to confirm—or completely rule out—a blown gasket, then it's time to bring out the chemical block tester.

This test is extremely accurate. The only reason I don't place it at the very beginning is because the first three tests will catch about 95% of blown head gasket cases (and you don't have to buy any extra tools). But in that remaining 5%—where the failure is subtle—a block tester is the one that gives you a solid answer.

This is how the test works:

• You pour a special blue chemical into the tester (see photo above).
• The tester is placed on the open radiator neck. Depending on coolant level, you may need to drain a little to allow the tester to draw air from inside the radiator.
• Next, you squeeze the rubber bulb to pull air from the radiator up through the fluid chambers. As the air bubbles through the liquid, it will trigger a chemical reaction.
• Start the engine and let it idle while you perform the test.
• If the blue chemical turns yellow (gasoline engines): Combustion gases are present in the cooling system. This confirms a blown head gasket, a cracked cylinder head, or even a cracked block.
• If the blue chemical stays blue: No combustion gases are leaking into the cooling system. This rules out a head gasket, block, or cylinder head problem.

You can shop for a block tester here:

More 4.7L V8 Jeep Grand Cherokee Diagnostic Tutorials

If you'd like to check out more step-by-step diagnostic guides, I've put together a complete list of Jeep 4.7L V8 Grand Cherokee tutorials here:

• Index of 4.7L V8 Jeep Grand Cherokee Articles

In that section, you'll find several hands-on test tutorials. Here are just a few examples: