How To Test For A Blown Head Gasket (2000-2009 4.7L V8 Dodge Dakota And Durango)

In this tutorial, I'll walk you through the exact step-by-step tests I use to confirm a blown head gasket —no guesswork involved.

These are real-world methods that I've used (and that professional techs rely on) in the field for years —and two of them don't require any tools at all.

Whether your 2000–2009 Dodge Dakota or Durango's 4.7L V8 won't start, overheats shortly after starting, or runs rough for no obvious reason, you'll learn how to zero in on a head gasket failure —if that's what's really going on.

Let's jump into the first test and see what your Dodge is trying to tell you.

APPLIES TO: This tutorial applies to the following vehicles:

• 4.7L V8 Dodge Dakota: 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.
• 4.7L V8 Dodge Durango: 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.

ENGINE NO-START DIAGNOSTICS:

• How To Diagnose A No Start (2000-2009 4.7L V8 Dodge Dakota).

CYLINDER MISFIRE DIAGNOSTICS:

• How To Diagnose A Misfire (2000-2009 4.7L V8 Dodge Dakota).

Read This Before You Start

TIP 1 –Let the engine cool down first: If your Dakota or Durango has been running, do not pop open the coolant cap.

The cooling system builds pressure when hot, and opening the cap too soon can cause scalding-hot coolant to spray out unexpectedly. That's a quick way to get badly burned.

Always let the engine cool down completely before opening the system. And when you do, wear gloves and eye protection —safety first, always.

TIP 2 –Compression testing is a two-person job: On this 4.7L V8, you'll need a helper inside the cab to crank the engine while you're down at the engine hooking up the gauge.

Before your helper turns the key, make sure you're clear of the engine bay. Once you've recorded the reading, have them hop out so you can get set up for the next cylinder.

TIP 3 –Keep hands clear of belts and fans: If you're doing a compression test or briefly running the engine during your diagnostic, keep your hands and clothing away from moving belts, pulleys, and fans.

Symptoms Of A Blown Head Gasket

On the 4.7L V8 Dodge Dakotas and Durangos, a blown head gasket usually happens after the engine has gotten way too hot. When this happens, you'll typically run into one of two scenarios:

• No-start condition: The damage to the head gasket is severe enough that the engine won't start at all.
• Starts but overheats quickly: The engine fires up, runs for a bit, but the temperature climbs rapidly —usually within just a few minutes of running.

Below are some other red flags that point to a blown head gasket issue:

• Overheating mystery: Your Dodge is overheating, and you've already ruled out the thermostat and radiator fan motor as the problem.
• Sweet-smelling white smoke: There's thick white smoke coming from the tailpipe, and it smells like antifreeze is (which is getting cooked in the combustion chamber).
• Cranks but won't fire up: The engine won't start —but you know the ignition and fuel systems are working:
  • Spark check passed: You've confirmed all 8 ignition coils are firing properly.
  • Fuel system OK: You ran a fuel pressure test and verified the pump is delivering pressure.
• Milkshake oil: The engine oil looks milky or frothy —a telltale mix of coolant and oil that points to head gasket failure.

TEST 1: Engine Oil Mixed With Coolant

This is the first thing I check whenever I suspect a blown head gasket —and it's one of the easiest to do. Just pull the dipstick and take a close look at the engine oil. If it's got a milky or frothy look, you may have coolant getting into the oil.

When coolant leaks into the crankcase, it mixes with the motor oil and turns it into a creamy mess —kind of like coffee with way too much creamer. That's a clear warning sign of a blown head gasket.

Here's how to check for it:

1. 1

   Pop the hood and locate the dipstick.

2. 2

   Pull the dipstick out and check the condition of the oil stuck to it.

3. 3

   Look closely at the color and texture of the oil.

4. 4

   You'll usually see one of two things:
   
   1: The oil looks like a tan-colored milkshake —thick and creamy.
   
   2: The oil looks clean and normal, with no signs of coolant contamination.

So what do these results mean? Let's break it down:

CASE 1: Oil is milky and off-white (like a thick creamed coffee) Unfortunately, this points to a blown head gasket.

Here's how that happens:

1. The engine overheats badly, warping the aluminum cylinder heads.
2. The head gasket can't maintain a proper seal anymore.
3. Coolant seeps into the oil passages and down into the oil pan.
4. As oil and coolant blend together, the result is that thick tan sludge you're seeing.

CASE 2: Oil looks normal, no discoloration or sludge That's good news —but don't relax just yet. A clean dipstick doesn't completely rule out a head gasket issue.

Some head gasket failures don't let coolant into the oil. Instead, combustion gases escape into the cooling system. To dig deeper, move on to the next test: TEST 2: Compression Pressure And/Or Exhaust Gas Exiting The Radiator.

TEST 2: Compression Pressure And/Or Exhaust Gas Exiting The Radiator

This test is quick, simple, and can give you a big clue about a possible head gasket failure. What you're doing here is cranking the engine with the coolant cap removed —and watching what the coolant does.

If the coolant level stays calm and undisturbed while cranking, that's a good sign. But if the coolant suddenly shoots up or gets violently pushed out, it means combustion gases are getting into the cooling system —a common symptom and result of a blown head gasket.

IMPORTANT SAFETY TIP: Never do this test on a hot engine. Let the truck cool off completely (at least an hour) before removing the cap. Hot coolant under pressure can spray out and cause serious burns.

NOTE: To perform this test, make sure you're removing the correct cap —not the coolant reservoir cap where you add coolant.

On the Dakota:

• 2000–2004 models: The cap you need is located on the upper radiator hose.
• 2005–2009 models: The cap is on the radiator itself.

On the Durango:

• 2000–2003 models: The cap is on the upper radiator hose.
• 2004–2009 models: You'll find the cap on the radiator.

Here's how to safely run this test on your Dodge Dakota or Durango:

1. 1

   Make sure the engine is cold, then remove the cap from the upper radiator hose or the radiator (depending on your vehicle's specific setup).

2. 2

   Check the coolant level. If it's low, top it off with water just to get a visible level at the neck.

3. 3

   Have a helper crank the engine while you observe the coolant. Stand off to the side for safety.

4. 4

   Watch what happens:
   
   1: The coolant suddenly surges or shoots upward —as the engine cranks.
   
   2: The coolant stays still and undisturbed —no bubbling, no rising.

Let's break down what those results tell us:

CASE 1: Coolant shot out of the tank when cranking. This is a strong sign that one or both head gaskets are blown.

Combustion gases are escaping from a cylinder, passing through the gasket, and pressurizing the cooling system. You don't need to do more tests —this alone confirms the problem.

CASE 2: Coolant stayed put, no movement. This is the normal and expected result. It tells us that —at least during cranking— there's no obvious leak of combustion gases into the cooling system.

So here's what to do next based on your symptoms:

• The engine runs, misfires, or idles rough, but doesn't overheat: Go to TEST 3: Checking Cylinder Compression.
• The engine runs fine, but overheats shortly after starting: Go to TEST 4: Using A Chemical Block Tester.

TEST 3: Checking Cylinder Compression

Sometimes a head gasket blows in a very specific way —right between two neighboring cylinders. When that happens, the engine will still start and run, but it'll misfire due to zero compression in those two cylinders.

What makes this kind of failure tricky is that you won't see the usual warning signs. No milky oil, no bubbling coolant, nothing leaking externally. The head gasket is still doing its job in most areas —except for the section between those two adjacent cylinders.

The best way to catch this type of problem is with a targeted compression test —no need to check all eight cylinders if you've already narrowed it down to the ones misfiring.

NOTE: You can find a more detailed explanation of the compression test in this step-by-step guide: How To Test Engine Compression (2000-2009 4.7L V8 Dodge Dakota And Durango).

Here's how to run this test on your 4.7L Dodge V8:

1. 1

   Identify the two misfiring cylinders. They'll be next to each other on the same cylinder bank.

2. 2

   Disable the ignition system to prevent the engine from starting during the test.
   
   You can disable ignition system by unplugging all 8 ignition coil from their connectors.

3. 3

   Disable the fuel system by either pulling the fuel pump relay (if applicable) or unplugging the injectors.

4. 4

   Remove the spark plugs from both cylinders you're testing.
   
   CAUTION: Don't drop the plugs —the porcelain insulator can crack, which could create a misfire later.

5. 5

   Thread in the compression tester by hand into the first spark plug hole. Don't use a wrench —hand-tight is all you need for a good seal.

6. 6

   Have your helper crank the engine while you watch the gauge needle.

7. 7

   Once the needle stops climbing, record the PSI reading along with the cylinder number.

8. 8

   Repeat the test for the second cylinder.

Now let's look at what those readings tell us:

CASE 1: Both cylinders have normal compression. Good news —that rules out a blown gasket between those two cylinders.

If you're still seeing symptoms that suggest a head gasket issue, jump to TEST 4: Using A Chemical Block Tester.

CASE 2: Both cylinders read 0 PSI. That confirms the gasket has failed between those two neighboring cylinders.

The combustion pressure is escaping directly between them, leaving you with no compression in either one —and a steady misfire you can't get rid of until the gasket is replaced.

Let me walk you through a real-world example. Say I'm working on a Dodge Dakota and I get the following compression readings:

• Cylinder #1 = 170 PSI
• Cylinder #2 = 165 PSI
• Cylinder #3 = 0 PSI
• Cylinder #4 = 172 PSI
• Cylinder #5 = 0 PSI
• Cylinder #6 = 168 PSI
• Cylinder #7 = 174 PSI
• Cylinder #8 = 175 PSI

That pair of zeros on #3 and #5? That's the giveaway. The head gasket between those two cylinders is toast. Now, in your case, it might be cylinders #1 and #3, or #4 and #6 —the key is this: both will have zero compression and they'll sit side by side.

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

Sometimes a head gasket can fail in a sneaky way. It won't mix coolant into the oil, it won't cause misfires, and it won't make the coolant shoot out of the reservoir. The idle might even be smooth.

But the engine still overheats within a few minutes of starting —and you're left scratching your head wondering what the heck is going on.

When that happens, the best tool for the job is a combustion leak detector —also known as a block tester.

Here's what the typical symptoms look like before using this test:

• No milky oil: The engine oil looks totally normal.
• No coolant geysers: The coolant doesn't bubble or spray when cranking with the cap off.
• Engine runs smooth: No misfires or rough idle.

The only red flag? The temperature gauge climbs fast, and you've already ruled out the usual suspects like thermostat or fan clutch. That's when a chemical block test can help you confirm whether combustion gases are sneaking into the cooling system.

Here's how the block tester works:

• Step 1: Fill the tester's chamber with the included blue detection fluid (see product instructions for how much to use).
• Step 2: Place the tester on the radiator neck —not the reservoir. You may need to drain a little coolant so there's space for air at the top of the radiator.
• Step 3: Start the engine and let it idle.
• Step 4: Squeeze the rubber bulb to draw air from the radiator into the tester. The air bubbles through the fluid.
• Step 5: Watch for a color change. If the blue fluid turns yellow, that's a positive result —combustion gases are entering the radiator.
• Step 6: If the fluid stays blue, no combustion gases are present —which means your head gasket, cylinder heads, and block are likely OK.

A positive result means one of the following:

• Blown head gasket.
• Cracked cylinder head.
• Cracked engine block.

You can grab a block tester online here:

Disclosure: As an Amazon Associate, I earn from qualifying purchases. Buying through these links helps support this site at no extra cost to you. I truly appreciate it!

Frequently Asked Questions

Should I replace both head gaskets?

Yes, both head gaskets should be replaced, even if only one has failed. When the engine overheats, both banks are exposed to the same heat stress, and the second gasket has likely been damaged too.

The other gasket is gonna fail soon —it's just a matter of time. Replacing them together is gonna save you time, money, and help you avoid doing the job all over again.

Should I resurface the cylinder heads?

Yes —especially if the engine overheated. Heat warps aluminum, and if the heads aren't flat, the new gasket won't seal right.

I recommend having a machine shop check both cylinder heads. If they're warped, they'll machine them flat again —just enough to restore the sealing surface without messing with compression or timing.

I've seen a lot of head gasket jobs fail early because the heads weren't resurfaced. Don't skip this step —it's worth it.

Can the heads be resurfaced too much?

Yes. The machine shop can only shave off a certain amount —go too far, and it'll mess with compression and valve timing.

But don't worry —any decent shop knows your 4.7L's specs and will resurface just enough to make the heads seal properly without causing issues.

Should I try a "blown head gasket repair" in a can?

I don't recommend it —but let's look at both sides first.

These sealers work sometimes, but only if the head gasket failure is minor —like a small coolant leak into the combustion chamber. Even then, it's hit or miss.

The big risk? The sealer circulates through the entire cooling system, not just the head gasket area. Over time, it can clog up the radiator, the heater core, and the engine's coolant passages —basically choking off the system's ability to cool the engine properly.

If you do end up replacing the head gasket later, you'll also have to deal with the mess: that hardened sealer can gunk up everything, and cleaning or replacing those parts adds more cost to the job.

I get it —a head gasket job is expensive. So I don't blame folks for trying a can of sealer first. But if your engine's already overheating, or losing coolant fast, odds are it won't help. And if it does "work", it's usually temporary.

More 4.7L V8 Dodge Dakota And Durango Tutorials

There are quite a few 4.7L V8 Dodge Dakota And Durango 'how to' tutorials and wiring diagrams you can find here:

• 4.7L V8 Dodge Dakota And Durango Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Throttle Position Sensor (2000-2007 4.7L V8 Dodge Dakota And Durango).
• How Often Should I Replace The Spark Plugs? (2000-2009 4.7L V8 Dodge Dakota And Durango).
• How To Test The Alternator (2001-2002 4.7L V8 Dodge Dakota And Durango).
• How To Test The Fuel Pump (2000-2007 4.7L V8 Dodge Dakota And Durango).