TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)
In some cases a head gasket has failed, but the first three tests are not able to confirm that it is.
In other words, even though one of the head gaskets has failed, the engine coolant isn't mixed with the engine oil, the coolant within the radiator isn't being shot out of the open coolant tank (while cranking the engine), and engine compression was okay. Yet the engine is overheating for no apparent reason at all.
In these hard to diagnose blown head gasket cases, the only way to find out if the head gasket is blown (or not) is to do a block test with a block tester.
You do have to buy (or borrow) the block tester, but this tool is worth every penny since it's a test that gives you a very accurate test result.
In a nutshell, this is how a block tester works:
- A blue liquid chemical, which is blue in color, is placed in the tester (see photo above).
- The tester assembly is then placed on the open radiator neck (you may have to drain some of the coolant in the radiator since this tool needs to ‘gulp’ some of the air inside the radiator).
- The engine is started.
- The rubber bellow is then squeezed to suck in the air up through the two fluid-filled chambers. As the air bubbles up through the fluid, it will cause a chemical reaction.
- If the blue chemical turns yellow (for gasoline engines), combustion gases are entering the radiator. This result confirms a head gasket failure, a cracked block, or a cracked cylinder head issue.
- If the blue chemical doesn't change color, you can conclude that you don't have a head gasket failure, a cracked block, or a cracked cylinder head issue.
Where can you get the chemical and block tester? At your local auto parts store or here:
Frequently Asked Questions
1.) Do I need to remove both cylinder head?
Yes, if you have confirmed that the engine has a head gasket failure, you have to remove and check both cylinder heads for cracks and warpage.
1.) How can I tell if the cylinder head is cracked?
The cylinder head has to be removed and visually inspected. If the crack is wide enough, you'll be able to easily see it.
Sometimes, a visual inspection proves inconclusive, this is why it's important to let a machine shop pressure test it for you.
2.) Do I need to resurface the cylinder head?
YES, you need to resurface both cylinder heads! You should never reinstall the cylinder head without first having an automotive machine shop resurface it. Especially if your Ford's engine overheated.
Now, of course, if you (or the machine shop) have checked it with a straight-edge and there's no warpage then, and only then is the cylinder head not resurfaced.
Related Test Articles
There are several more 3.0L, 3.8L Ford car (or mini-van, pick up) specific ‘how to’ tutorials that I've written for your troubleshooting and diagnostic benefit. The articles that are here in this web site, you can find them here: Ford 3.0L, 3.8L Index Of Articles.
At easyautodiagnostics.com, you'll find the following articles:
- How To Test The Ford V6 Ignition Coil Pack.
- How To Test The Ignition Control Module (Older 3.0L And 3.8L With A Distributor).
- How To Test The MAF Sensor.
- How To Test The Throttle Position Sensor (TPS).
If this info saved the day, buy me a beer!
