Compression Testing - Hot or Cold?
Posted: Sun Sep 29, 2019 7:46 pm
I know this is widely discussed generally and I have seen a thread on here regarding the testing procedure but not so much the ' hot or cold' bit so just thought I would see which way you guys have done it ? I ought to add at this stage the car in question is the Dolly Sprint, which of course has an Alloy head, although the question could be asked for our heads also.
So today having now purchased a new Sealy tester with all the relevant fittings and extentions,off we jolly well go in search of some actual readings. Here are the results which quite frankly stumped me. Any comments are welcome
Brand new tester
Brand new 038 battery
All spark plugs removed
Throttle wide open
Coil and fuel line disconnected
COLD engine as purchased as non- runner.
All 4 cylinders pushed the gauge up to its high reading in 4 crank overs. I did each one twice - and i got 130 for each cylinder over two readings,give or take a couple either way. I was not expecting that. Father in law mentions 'Perhaps as it is cold it may not read correctly' - so i have spent several hours now trawling the net and it realy seems to be 50/50 with the rights and wrongs of doing this hot or cold.
It has been quite interesting - with some saying when cold the engine is at it's worst for sealing so this is the correct situation to test, some say they would NEVER do a hot test on an ally head for fear of stripping threads removing a hot plug. Etc Etc !!!! Any thoughts?
So regarding the Dolly - with all four generally around 130 - cold - am i right in thinking that even though this may not be the correct pressure reading, there is not one or two way diferrent to another - would that indicate the head and gasket is ok? That is the impression i have, based on what I been reading this afternoon.. I have not found in any of what i have read to say on the lines of ' a cold reading MAY NOT find issues of head or gasket failure. So on that, things are a little more upbeat, i just wonder if i get any replies that agree. Interesing - i think The only thing that still concerns is the truly shocking state of the oil that we drained out - it was way overfull - this was before turning the engine over. On the dipstick it looked pristine. On draining a good litre or so out to bring the level down ,what came out was awful. Water sinks to the bottom....So this is very puzzling And this MUST of been the reason for the high level in the sump.
I forgot to add that all four plugs looked good - a little sooty but not wet, and looking through plug holes all four crowns looked ok and dry. Basically it all SEEMS to check out?
So today having now purchased a new Sealy tester with all the relevant fittings and extentions,off we jolly well go in search of some actual readings. Here are the results which quite frankly stumped me. Any comments are welcome
Brand new tester
Brand new 038 battery
All spark plugs removed
Throttle wide open
Coil and fuel line disconnected
COLD engine as purchased as non- runner.
All 4 cylinders pushed the gauge up to its high reading in 4 crank overs. I did each one twice - and i got 130 for each cylinder over two readings,give or take a couple either way. I was not expecting that. Father in law mentions 'Perhaps as it is cold it may not read correctly' - so i have spent several hours now trawling the net and it realy seems to be 50/50 with the rights and wrongs of doing this hot or cold.
It has been quite interesting - with some saying when cold the engine is at it's worst for sealing so this is the correct situation to test, some say they would NEVER do a hot test on an ally head for fear of stripping threads removing a hot plug. Etc Etc !!!! Any thoughts?
So regarding the Dolly - with all four generally around 130 - cold - am i right in thinking that even though this may not be the correct pressure reading, there is not one or two way diferrent to another - would that indicate the head and gasket is ok? That is the impression i have, based on what I been reading this afternoon.. I have not found in any of what i have read to say on the lines of ' a cold reading MAY NOT find issues of head or gasket failure. So on that, things are a little more upbeat, i just wonder if i get any replies that agree. Interesing - i think The only thing that still concerns is the truly shocking state of the oil that we drained out - it was way overfull - this was before turning the engine over. On the dipstick it looked pristine. On draining a good litre or so out to bring the level down ,what came out was awful. Water sinks to the bottom....So this is very puzzling And this MUST of been the reason for the high level in the sump.
I forgot to add that all four plugs looked good - a little sooty but not wet, and looking through plug holes all four crowns looked ok and dry. Basically it all SEEMS to check out?