Compression test results-cold/hot engine

Blownoiler

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I recently had a friend come over to test run his new compression gauge on my Isuzu 4jg2, as I had 2 dead glow plugs so had to replace them anyway. The workshop manual specs are 440 psi hot, the lower limit is 340 psi before rebuilding is required.
He decided to test the engine cold first, to get an idea of the hot to cold variation in pressure.
First test result with cold engine, cylinder 1 to 4
no. 1- 419
no.2- 420
no.3- 420
no.4- 421
Talk about consistent! Then the engine was warmed up to normal operating temp and another test gave these figures-
no.1- 498
no.2- 480
no.3- 477
no.4- 460
Wow, that no. 1 cylinder really sealed up well when hot.
His next test was after an engine oil flush and change. First off, half a litre of kerosene was added to the engine oil and the engine was then run for around 20 minutes at a fast idle (1500 rpm), the oil dropped, filter changed and new 15/40 semi synthetic oil poured into the motor (the dumped oil was 20/50 mineral). Then the engine was ran for 10 minutes to get it up to temp for another hot test, results were-
no. 1- 481
no. 2- 460
no. 3- 458
no. 4- 461
After seeing the pressures decrease from no. 1 to 4 in the first hot test, this time he went back to cylinder 1 after doing no. 4 and got 480, so at least there was some consistency present!
The time to test all 4 cylinders was only around 10 minutes, still I'm inclined to wonder if the last cylinders tested lost some heat from cranking over the engine while testing the front 2, which would explain the lower pressure numbers going from 1 to 4. Has anyone else tried a hot/cold test? and if so what sort of pressure change did you see?
 

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