Testing for a blown head gasket on your 2.0L Mazda 626 (2.0L Mazda MX6) isn't hard. In this tutorial I'll show you the 4 basic tests that are done to find out. So, if the engine in your Mazda has severely overheated and doesn't start or it starts and runs but overheats (and you've already confirmed that the fan, thermostat and water pump work) and you suspect that you've got a blown head gasket on your hands... this is the tutorial for you.
These 4 simple tests, which are explained in a step-by-step manner, will let you know if the head gasket has blown.
Here are the contents of this tutorial at a quick glance:
- Symptoms of a Blown Head Gasket.
- TEST 1: Engine Oil the Color of ‘Coffee With Too Much Cream’.
- TEST 2: Coolant Shooting Out From Open Radiator.
- TEST 3: Engine Compression Test.
- TEST 4: Using a Chemical Block Tester (Combustion Leak Tester).
- More 2.0L Mazda Tutorials.
You can find this tutorial in Spanish here: Cómo Probar el Empaque de Cabeza (2.0L Mazda 626 y MX6) (at: autotecnico-online.com).
The most common cause of a blown head gasket is severe engine overheating. This is usually caused by one of three conditions/problems:
- The radiator fan motor stopped working.
- Engine lost all of the coolant (due to a leak somewhere in the cooling system).
- Thermostat failed and stayed stuck in its closed position (preventing the coolant from circulating).
Now, the most common symptoms a blown head gasket are:
- Your Mazda 2.0L 626 is overheating. You've ruled the fan motor or thermostat.
- White smoke is coming out of the tail-pipe and it smells like anti-freeze.
- The engine won't start.
- You have already verified it's not an ignition system problem because you have spark coming out at all of the spark plug wires.
- You know it's not a lack of fuel, because you have verified that the fuel pump is delivering fuel to the fuel injectors.
- The engine oil is thick and tan to off-white color (like ‘coffee with too much creamer’).
NOTE: The majority of the Mazda 2.0L engines use a multi-layer steel head gasket. This type of head gasket is prone to leaking oil as the engine accumulates miles and age. Amazingly, this problem usually doesn't cause the engine to overheat.
This first test is a simple test and checks for one of the most common results of a blown head gasket: coolant mixing with the engine oil.
We can easily find out if this has happened to your engine by simply checking the color of the engine oil. If it's mixed with coolant, it'll be the color of ‘coffee with too much creamer’.
These are the test steps:
Open your Mazda's hood and check the condition of the engine oil by pulling out the engine oil dipstick.
You're gonna' see one of two things:
1.) The engine oil will be a creamy tan/ off-white color or...
2.) The engine oil will be its usual normal color.
Alright, let's interpret the color of the engine oil:
CASE 1: The color of the oil is a light tan, like coffee with too much cream, and your Mazda 2.0L 626 starts and overheats or does not start. This test result tells you that you have a bona-fide blown head gasket on your hands.
CASE 2: The color of the engine oil is normal. So far so good, since this is the correct test result.
But more testing is necessary to make sure the head gasket is not blown (especially if your Mazda 2.0L 626 is overheating or not starting). Your next step is to go to: TEST 2: Coolant Shooting Out From Open Radiator.