Interesting Compression Test Experience

warmblood58 · Post by **warmblood58** » 02 Apr 2016, 19:29

So I thought I still had a gas compression gauge but no, just a diesel comp gauge so I borrowed a loaner from my flaps and had engine warm ('95 850 T5-r). First cylinder -0, second - 0 . . . . I was getting worried but knew something had to be wrong with gauge as car just passed smog. Cylinder 3 also 0 so I returned faulty gauge and went to Harbor Freight and picked up one of their gauges. This time, I was getting readings Cold of 110 across the board and again, I knew something had to be wrong with gauge - throttle body valve was open during all testing. Fortunately, the HF kit came with an old school compression style adaptor so I had my gf crank while I pushed compression fitting tight against spark plug ports and finally got these readings of 155, 155,150,155, 160 . . . pretty even! I was relieved to say the least! I will most likely take warm readings next week but curious if anyone knows (in general) the variance between hot and cold compression test readings? Perhaps 10% higher? Thanks!

Post by **rspi** » 02 Apr 2016, 20:40

No set percentage. Sometimes there is very little. Make sure you have a real strong battery or use some sort of jump box.

Post by **j-dawg** » 03 Apr 2016, 10:12

The most important thing is really consistent compression across all cylinders.

warmblood58 · Post by **warmblood58** » 03 Apr 2016, 14:38

yea, I must say it was nice to see the final numbers with little variation