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Today we are going to cover the different types of fittings for compression testing on both automotive and diesel engines. Compression testing is one of the easiest way to check an engine to try and locate an internal problem by testing each cylinder against each other and what your service manual recommends as an acceptable reading for that engine. If you have one cylinder reading very low it is very likely the cause of your problems. It could be anything from a stuck valve to worn piston rings.

Today we are going to show the different fitting on your typical compression adapters.

This is your standard universal automotive style compression gauge adapter. They are universal in the industry and work with most 300PSI compression gauges.  When you move to high compression diesel engines the fittings change. This is done for safety. Most diesel compression gauges are 2000 PSI.  We never recommend that you try and adapt an automotive style compression gauge to work with a diesel engine.  I know you have the equivalent of a beach front condo invested in your tool box. It is well worth it not to be known as lefty to go ahead and buy the proper gauge. Feeding 1500+ PSI to a gauge meant to see 300PSI is a catastrophic failure waiting to happen.

This is for the most part the industry standard for high compression diesel engine compression adapters.  This is the same fitting as you will find on your 2000PSI compression gauges. It is used by us at Apex Tool Company, MAC Tools, MATCO Tools, OTC & Others.  From some basic research the best I have came up with is that this adapter was invented by Foster Fittings.

With anything you have an exception to the rule. This fitting is Snap-On’s heavy duty fitting. It appears the same as the Universal automotive and is very close. It is just different enough that the universal automotive couplings will not grab and make a proper seat.  I have a feeling if you try and make it work it will be like firing a potato gun off in your shop.

I was digging through our stock of different compression adapters for this blog post and came across this one from Snap-On. Of all the Snap-On adapters we had in the building, they have restricted the flow.  I checked the equivalent unit we sell and can not figure out the need for extra flow.  Until I hear otherwise, I am chalking this one up to a design anomaly.

If you have any questions or comments feel free to contact me.  Be sure to check out Apex Tool Company for our full line of Diesel Compression Test Equipment.  Just remember there is no such thing as a free coat off a tool truck. 

Happy wrenching,

Fred Neff