compression test

[danielr]

I ride a 1997 SL SOHC, 185.000 Km, standard transmission.
Oil is changed every 3500 Km, I use Castrol Synthetic 5W30, and K&N
oil filter.
I know; some of you might believe it is a waste of money; but I am a
FIRM believer of preventive maintenance.
I am VERY satisfied with this car.
Question:
Which should be range (max / min) of values resulting in a compression
test for this engine?
Thanks in advance for your assitance.
Regards,

danielr

 

[Oppie]

Rule of thumb is 125-150 psi depending on the compression ratio of the
engine. Make the compression test with all plugs removed, the ignition coil
disconnected and wide open throttle. Crank for 5 seconds to get a stable
reading. Log readings, do all cylinders and then repeat. Make sure you get
consistent readings on each cylinder. Readings between all cylinders should
be within 5-10 psi. If you get a cylinder that reads low, put a couple of
squirts of oil into the cylinder and repeat the test. If the reading comes
up, most likely worn piston rings. If the reading stays low, could be head
gasket or valves. Don't forget to label the plug wires as you remove them to
make sure they all go back in the right places.

 

[Private]

Rule of thumb is 125-150 psi depending on the compression ratio of the
engine. Make the compression test with all plugs removed, the ignition
coil disconnected and wide open throttle. Crank for 5 seconds to get a
stable reading. Log readings, do all cylinders and then repeat. Make sure
you get consistent readings on each cylinder. Readings between all
cylinders should be within 5-10 psi. If you get a cylinder that reads low,
put a couple of squirts of oil into the cylinder and repeat the test. If
the reading comes up, most likely worn piston rings. If the reading stays
low, could be head gasket or valves. Don't forget to label the plug wires
as you remove them to make sure they all go back in the right places.

@278,000 km my 96 SOHC 5sp pumped to
155 lbs dry and warm, and 230-270 lbs with oil added,
(the 230 cylinders had less oil than the 270 ones.)

Adding more oil will seal the rings better but will also raise the
compression ratio, I should have measured the added oil better by counting
the oil can squirts and adding the same number.

Previous test @178,000 km pumped 130/128/131/130 warm and 128/126/128/125
cool and 220/185/225/215 oiled warm and 190/155/185/185 oiled cool. The
center cylinders were retested 1,000 km later both 160 psi warm. I suspect
a piece of crud on valve in #2 cyl during first oiled test.

YMMV depending on accuracy of your gauge, I think mine is OK and was top
quality and quite expensive in its day but is about 35 yrs old. As Oppie
topposted, your results are probably more important relative to each other
cylinder after dry and wet testing, as these results will all be with the
same tester. Record your results in your maintenance log and then you can
compare them in another 50 or 100,000 km to detect any trends.

Many mechanics will debate the value of compression testing and will often
advocate for a cylinder leak down test as being a superior test, but a plain
compression test is easier and uses simpler tools and will quickly find
large problems like one bad cylinder or valve.

Good luck, YMMV, make sure you have locked the throttle butterfly valve in
open position for test, IMHO warm is best for reliable results and
consistency.

 

[danielr]

@278,000 km my 96 SOHC 5sp pumped to
155 lbs dry and warm, and 230-270 lbs with oil added,
(the 230 cylinders had less oil than the 270 ones.)

Adding more oil will seal the rings better but will also raise the
compression ratio, I should have measured the added oil better by counting
the oil can squirts and adding the same number.

Previous test @178,000 km pumped 130/128/131/130 warm and 128/126/128/125
cool and 220/185/225/215 oiled warm and 190/155/185/185 oiled cool.  The
center cylinders were retested 1,000 km later both 160 psi warm.  I suspect
a piece of crud on valve in #2 cyl during first oiled test.

YMMV depending on accuracy of your gauge, I think mine is OK and was top
quality and quite expensive in its day but is about 35 yrs old.  As Oppie
topposted, your results are probably more important relative to each other
cylinder after dry and wet testing, as these results will all be with the
same tester.  Record your results in your maintenance log and then you can
compare them in another 50 or 100,000 km to detect any trends.

Many mechanics will debate the value of compression testing and will often
advocate for a cylinder leak down test as being a superior test, but a plain
compression test is easier and uses simpler tools and will quickly find
large problems like one bad cylinder or valve.

Good luck, YMMV, make sure you have locked the throttle butterfly valve in
open position for test, IMHO warm is best for reliable results and
consistency.- Hide quoted text -

- Show quoted text -

Hi "Oppie"

Thank you very much for your help.
Regards,

danielr

 

[Oppie]

Hi "Oppie"

Thank you very much for your help.
Regards,

danielr

And thank you 'Private' for your input also.

 

[navaidstech]

Let's see... I've got a 92 SL1 SOHC with 553,000 km on it. Been
putting Castrol Synth in it and a cheap Motomaster oil filter since
the car had 100,000 km on the odometer. I change my oil every 10,000
kms.
Did a compression test about a month ago and got 185-190 PSI in all
cylinders dry and cold. Didn't bother putting any oil in the cylinders
to do further checks, since I was happy with the readings.
Hope this helps!

Alex

 

[danielr]

Let's see... I've got a 92 SL1 SOHC with 553,000 km on it. Been
putting Castrol Synth in it and a cheap Motomaster oil filter since
the car had 100,000 km on the odometer. I change my oil every 10,000
kms.
Did a compression test about a month ago and got 185-190 PSI in all
cylinders dry and cold. Didn't bother putting any oil in the cylinders
to do further checks, since I was happy with the readings.
Hope this helps!

Alex

Thanks Alex;
It certainly does, as it provides a reference to effectiveness of the
same oil I'm using.
Thank you very much.again
danielR

 

[navaidstech]

Thanks Alex;
It certainly does, as it provides a reference to effectiveness of the
same oil I'm using.
Thank you very much.again
danielR

No problem Daniel. Good luck!

 

[Private]

Let's see... I've got a 92 SL1 SOHC with 553,000 km on it. Been
putting Castrol Synth in it and a cheap Motomaster oil filter since
the car had 100,000 km on the odometer. I change my oil every 10,000
kms.
Did a compression test about a month ago and got 185-190 PSI in all
cylinders dry and cold. Didn't bother putting any oil in the cylinders
to do further checks, since I was happy with the readings.
Hope this helps!

Alex

You should be happy with these numbers and your service life. I would
normally suggest verifying the compression test gauge but why tempt fate, if
it aint broke, etc., it is the cylinder variation that is most important
anyway.

Looks like you got a good one, keep it as long as you can and don't fix
anything that doesn't need opening up.

Good luck.

 

[navaidstech]

You should be happy with these numbers and your service life.  I would
normally suggest verifying the compression test gauge but why tempt fate,if
it aint broke, etc., it is the cylinder variation that is most important
anyway.

Looks like you got a good one, keep it as long as you can and don't fix
anything that doesn't need opening up.

Good luck.

Thanks for the words of encouragement.
I intend to keep the car as long as I possibly can although it got
really close to getting junked a couple of months ago.
One of the timing chain guides has shattered leaving the chain
rattling and car losing power. My wife was super happy as she wants me
to get rid of the car and buy something "decent".... well, I stuck to
my guns, ordered a new kit and replaced the chain, guides, sprockets,
etc...
Now the car runs like new and my wife ain't very happy about that! LOL

BTW... guys at work are having a tough time believing that the car
being as old as it is (18+ years) still runs on the original clutch
and the exhaust system (well, the muffler was replaced a few times,
but everything else is original)


Alex

 

[Oppie]

Thanks for the words of encouragement.
I intend to keep the car as long as I possibly can although it got
really close to getting junked a couple of months ago.
One of the timing chain guides has shattered leaving the chain
rattling and car losing power. My wife was super happy as she wants me
to get rid of the car and buy something "decent".... well, I stuck to
my guns, ordered a new kit and replaced the chain, guides, sprockets,
etc...
Now the car runs like new and my wife ain't very happy about that! LOL

BTW... guys at work are having a tough time believing that the car
being as old as it is (18+ years) still runs on the original clutch
and the exhaust system (well, the muffler was replaced a few times,
but everything else is original)


Alex

The Stainless Steel exhaust systems popular now (because of the acids in
catalytic converter exhaust eating out steel pipes) go on just about
forever. I used to have a Chrysler product that had 208K miles on the
original pipes. As with you, muffler only had been replaced three times.
Pipes were still good when we junked the rest of the car.