Tech Tip #19: Engine Diagnostics for Dummies

Dr. Diesel
Written by Dr. Diesel


Beginners guide to engine diagnostics

Dr. Diesel™ thinks these three diagnostics tools have withstood the test of time.

Engine Smoke

  • White smoke indicates water. Either coolant leaks, bad head gasket or a cracked head. Probably the latter if on a Perkins 4154 or 4108 marine engine.
  • Blue smoke is oil. This indicates that worn rings, guides or liners are dumping oil into the combustion chamber.
  • Black smoke is excessive fuel. Bad timing, worn injectors, leaking injection pump, etc. It could also be caused by a bad turbo if on a 1011/2011 Deutz in a concrete saw.


  • Bubbles in the coolant mean compression gases are entering the system. Maybe a bad head gasket? Oil in coolant suggests a cracked head, block or the oil lines may be incorrectly installed, this is a frequent problem on Continental flathead engines.


  • Smoke or pressure coming up the tube indicates a problem in the lower end (i.e. not the head), usually a bearing problem. Combustion and exhaust gases are pressurizing the crankcase as a result of worn rings or liner.

While the above diagnostics aren’t conclusive, you should confirm them with oil analysis, magnafluxing, pop tests, etc. We stock workshop manuals for Perkins, Deutz, Deere, Continental and Ford Industrial engines and could send one out to you immediately.


Dr. Diesel
Written by Dr. Diesel
Knowledge is power. Power to build ties to engine users. To build a relationship with our customers, we share with you our 105 years of knowledge in many ways. We have this special section called “Ask Dr. Diesel™” where you can pose questions about engines, transmissions, industrial hand clutches, exhaust scrubbers, etc.