How To Test For A Blown Head Gasket (1990-1993 2.3L Ford Mustang)

Testing for a blown head gasket on your 1990–1993 2.3L Ford Mustang isn't difficult, and it's something you can do yourself without having to take it to the shop.

In this tutorial, I'm going to explain the four tests used to pinpoint a blown head gasket. Two of these don't require any tools at all, and you can get them done in under five minutes.

The other two tests do need some tools. One is a compression test, which requires a compression tester, and the other is a block test, which requires a combustion leak detector.

Hopefully you don't have a blown head gasket on your hands, but if you do, these four tests will help you confirm it for sure.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.3L Ford Mustang: 1990, 1991, 1992, 1993.

Symptoms Of A Blown Head Gasket

A head gasket failure is almost always the result of severe engine overheating. So, if the engine in your 2.3L Ford Mustang has overheated and the head gasket has failed, you're going to see one or more of the following symptoms:

• Overheating: The engine runs hot, and you can't find an obvious reason for it.
• Oil and coolant mixing: The oil turns a milky color —looks like coffee with way too much creamer— from coolant leaking into the crankcase.
• White exhaust smoke: Thick, white smoke coming out of the tailpipe from antifreeze burning inside the cylinders.
• No-start condition: The engine will crank, but it just won't fire up.
• Cooling system overpressure: The radiator gets overpressurized and starts pushing coolant out whenever the engine idles or after you shut it off.

TEST 1: Oil The Color Of 'Coffee With Too Much Creamer'

The classic test (and the very first thing any automotive repair technician does when diagnosing a blown head gasket on any vehicle) is to pull out the engine oil dipstick and check the color and condition of the oil on the dipstick.

So, for our very first test, that's exactly what we're going to do. We can expect one of two results:

• Engine oil looks like coffee with too much creamer: This is a dead giveaway that the head gasket on your 2.3L Ford Mustang has failed.
• Engine oil looks normal: We're not out of the woods yet. The next step is to see if combustion pressures are leaking into the cooling system in TEST 2.

Let's get going:

1. 1

   Open your Ford Mustang's hood.

2. 2

   Pull out the engine's oil dipstick.

3. 3

   Check the color of the oil.

4. 4

   You'll see one of two things:
   
   1.) The engine oil will be a creamy tan/off white color and as thick as syrup.
   
   2.) The engine oil will be a normal color and viscosity.

Now, let's find out what each of the two results mean:

CASE 1: The color of the oil is a tan/off white color. This confirms that the head gasket on your 2.3L Ford Mustang is blown and needs to be replaced.

CASE 2: The color of the engine oil is normal. This is a correct and expected test result, but we still can't rule out a blown head gasket.

Your next step is to see if the engine is pushing exhaust/combustion/compression pressures into the cooling system. For this test, go to: TEST 2: Exhaust Gases Shooting Out Of The Radiator.

TEST 2: Exhaust Gases Shooting Out Of The Radiator

You're probably already aware that the head gasket's job is to seal the pressures created by the combustion cycle within the cylinder (compression, combustion, exhaust, etc.).

When the head gasket is in tip-top condition, it keeps these pressures sealed inside the cylinders and prevents them from entering the cooling system.

But if the head gasket has failed, combustion gases can escape into the coolant passages in the cylinder head and engine block, and then enter the cooling system.

So, for our next test, we're going to open the radiator, crank the engine, and see if the coolant inside the radiator gets shot out while cranking.

We can expect one of two results with this test:

• The coolant is pushed (shot) out from the open radiator neck, confirming that the head gasket is blown.
• The coolant remains undisturbed in the radiator, which is the correct and expected result.

CAUTION: Perform this test with a completely cooled engine. Never open the radiator if the engine has been running for any length of time, or you risk serious burns from escaping coolant. You can speed up cooling down your Mustang's engine by placing a fan over it.

Here's what to do:

1. 1

   Remove the cap from the radiator.
   
   Make sure the tank has enough coolant. If it's low or empty, add water or coolant until it reaches the proper level.

2. 2

   Have your helper crank the engine while you watch the coolant level from a safe distance.

3. 3

   You'll see one of two things:
   
   1.) The coolant inside the radiator shoots up or bubbles out.
   
   2.) The coolant level remains undisturbed —cranking the engine has no effect.

Here's how to read the results:

CASE 1: The coolant bubbled up or shot out. This is bad news —it confirms, without a doubt, that the head gasket on your 2.3L Ford Mustang has failed.

CASE 2: The coolant did not bubble or shoot out. This is the correct and expected result.

If your Mustang starts and runs but overheats for no clear reason, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

If your Mustang does not start, go to: TEST 3: Doing A Compression Test.

TEST 3: Doing A Compression Test

Another common head gasket failure is when a section of the gasket that sits between two side-by-side cylinders gets burned.

The result of this type of failure is that both of those cylinders lose compression. In other words, the compression of one cylinder gets pushed into the other and vice versa, creating two "dead" cylinders with 0 PSI. And since you've got two "dead" cylinders on your hands, the engine isn't going to start.

If you look at the image of the head gasket at the beginning of this tutorial, you'll notice it has suffered this type of failure (burned right between two side-by-side cylinders).

The way to confirm this type of head gasket failure is to do a compression test and see if we get 0 PSI from two side-by-side cylinders. And that's exactly what we'll do in this test section.

NOTE: You can find a more detailed explanation of the cylinder compression test —along with how to read the results— in this tutorial: How To Do And Interpret An Engine Compression Test (1990-1993 2.3L Ford Mustang).

OK, here's what you need to do:

1. 1

   Disable the ignition system.
   
   You can easily accomplish this disconnecting the ignition coil's electrical connector (if your vehicle has a distributor) or the ignition coil pack's electrical connector.

2. 2

   Disable the fuel system. It's important that fuel not be injected into the engine.
   
   You can do this by removing the fuel pump relay or the fuel pump fuse.

3. 3

   Disconnect all spark plug wires (from their spark plugs) and then take out all of the spark plugs.
   
   NOTE: Before you remove the spark plug wires, label them so that you'll be able to easily reconnect them to their proper original locations.

4. 4

   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.

5. 5

   Have a helper crank the engine while you observe the compression tester.

6. 6

   Once the gauge's needle stops climbing, have your assistant stop cranking the engine.

7. 7

   Write down the reading and what cylinder it belongs to (you can use the image in the image viewer to help you identify the cylinder) on a piece of paper.

8. 8

   Remove the compression tester and repeat the above steps in the remaining cylinders.

OK, let's take a look at what your results mean:

CASE 1: All cylinder compression readings where similar. These compression gauge readings confirm that the head gasket is OK and not burned at a point between two cylinders.

If you still suspect that your Mustang's head gasket is blown, especially if the engine overheated recently, your next step is to do a block test with a combustion leak detector. 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. Sorry for the bad news, the head gasket needs to get replaced.

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

Every now and then, you'll run into a head gasket failure that doesn't show symptoms. For example, you won't see coolant mixing with the engine oil (TEST 1).

You won't see coolant being shot out of the radiator (TEST 2), and compression looks good across all four cylinders (TEST 3). But the head gasket has still failed, and it's usually causing the engine to overheat within minutes of being started.

In these tough-to-diagnose cases, the only way to confirm if a head gasket failure is behind the issue is to do a block test with a combustion leak detector.

This is the same test you're paying for when you take your vehicle to the shop to diagnose a blown head gasket, and it's something you can do yourself.

Here's how the test works:

• A blue chemical solution is poured into the tester (see photo above).
• The tester is set on the open expansion tank neck. You may have to drain a little coolant to let the tool pull in radiator air.
• The engine is started.
• Squeeze the rubber bulb to draw air through the fluid chambers. The bubbling air reacts with the chemical.
• If the fluid changes from blue to yellow (on gasoline engines), combustion gases are present in the engine's cooling system. That means a blown head gasket, cracked block, or cracked cylinder head.
• If the fluid stays blue, then those issues are not present.

You can get the chemical and block tester at most auto parts stores or here:

Frequently Asked Questions

1.) How do I know if the cylinder head is cracked?

The head has to be removed for inspection. If the crack is obvious, you'll usually be able to spot it right away.

When a visual check isn't conclusive, that's where a machine shop comes in. They can pressure test the cylinder head to confirm whether or not it's cracked.

2.) Should the cylinder head be resurfaced?

Yes —the cylinder head should be resurfaced. Never reinstall it without first having an automotive machine shop do the resurfacing, especially if your Mustang's engine has overheated.

The only exception is if you (or the shop) check the cylinder head with a straight-edge and find no signs of warpage. In that case, resurfacing it isn't necessary.

3.) Is it worth trying a head gasket sealer in a can?

I don't recommend it, but I understand why their used.

The sealants will sometimes buy you time if the head gasket failure is very minor —like a small coolant seep into a cylinder. Even then, it's hit or miss.

The bigger concern is that the sealer circulates through the entire cooling system, not just the head gasket. It can clog the radiator, heater core, or coolant passages, which reduces the system's ability to keep your engine cool.

And if you eventually replace the gasket (and you will), you'll run into another headache: cleaning out hardened sealer. It gums up components and makes the repair more expensive.

Believe me, I get it —a head gasket job is costly and a lot of work even for a DIYer. That's why people reach for a can first. But if your 1990–1993 2.3L Ford Mustang is already overheating or losing coolant quickly, odds are the sealer won't solve it. And if it does, the "fix" usually doesn't last long.

More 2.3L Ford Mustang Diagnostic Tutorials

You can find a complete list of 2.3L Ford Mustang wiring diagrams and diagnostic tutorials in this index:

• 2.3L Ford Mustang Index Of Articles.