Tech Tip: How to diagnose a blown head gasket

A damaged (blown) head gasket may lower the cylinder’s compression causing longer spark burn (or firing) times than normal, as well as misfires, depending on the location and size of the failure.

By measuring the spark burn times and detecting misfires in each of the engine’s cylinders, which for an with a COP adapter-equipped ignition scope, or with an ignition analyzer like the General Technologies TA500 SmartTach+COP Multisystem Ignition Analyzer, then comparing the measurements between the cylinders, we can learn the following:

  1. One cylinder with longer burn times and/or misfires than the rest may indicate that it has low compression due to a compression leak to the crankcase, coolant system, etc.
  2. Longer burn time and/or misfires on a pair of contiguous cylinders (compared to the rest), may indicate low compression due to a leak between the two cylinders.

There are problems other than a blown head gasket that may cause longer than normal burn times and misfire readings, such as leaking valves, worn piston rings, fouled spark plugs, etc.  When a blown gasket is suspected, ignition measurements should be used in combination with other techniques, (looking for oil in the coolant, coolant in the oil, checking if there are hydrocarbons in the coolant, etc.,) to find the root cause.

Information provided by: General Technologies

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