How To Test For A Blown Head Gasket (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma)

A blown head gasket can be easily diagnosed with one of four tests. Two of these tests do not require any tools to perform!

This tutorial provides step-by-step instructions on how to complete all four tests. With your test results, you'll quickly determine if a blown head gasket is causing an engine no-start problem or an engine performance issue in your 2.5L Chevrolet S10 pickup or GMC S15 pickup.

You can find this tutorial in Spanish here: Cómo Probar Un Empaque De Cabeza (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.5L Chevrolet S10 Pickup: 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993.
• 2.5L GMC S15 Pickup: 1985, 1986, 1987, 1988, 1989, 1990.
• 2.5L GMC Sonoma: 1991, 1992, 1993.

Symptoms Of A Blown Head Gasket

A blown head gasket issue will usually cause one of two problems:

• An engine no-start problem.
• The engine starts but overheats immediately and for no apparent reason.

Here's a basic list of the symptoms you'll see when your 2.5L Chevrolet S10 pickup or GMC S15 pickup suffers a head gasket failure:

• The engine overheats for no apparent reason. All engine cooling system components (like fan clutch/motor, water pump, etc.) are working fine.
• White smoke is coming out of the tail-pipe and it smells like anti-freeze being cooked.
• The engine won't start.
• The engine oil is thick and a milky white color.

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

One of the most common results of a blown head gasket is coolant entering the crankcase and mixing with the engine oil.

When coolant mixes with engine oil, the resulting mixture is the color of coffee with too much creamer.

For our first test, we'll pull out the engine oil dipstick and check the color and viscosity of the oil adhering to it.

If the oil looks like coffee with too much creamer, you can conclude that the head gasket has failed.

If the engine oil looks OK, we'll proceed to the next test (TEST 2).

Let's get testing:

1. 1

   Open the hood.

2. 2

   Pull out the engine oil dipstick.

3. 3

   Check the color of the oil (sticking to the engine oil dipstick).

4. 4

   You'll see one of two results:
   
   1.) The engine oil looks like coffee with too much creamer.
   
   2.) The engine oil is its usual normal color.

OK, let's find out what your test result means:

CASE 1: The engine oil has the color of coffee with too much creamer. This test result confirms that the head gasket is blown on your 2.5L Chevy S10 (GMC S15, Sonoma).

CASE 2: The color of the engine oil is normal. This is the correct and expected test result.

The next test is to see if the engine's compression pressures are escaping into the engine's cooling system (radiator). For this test go to: TEST 2: Coolant Shooting Out From Open Radiator.