Wet Test Question...

[SD GST]

Well, I was driving my car last week and my friend who was behind me said that I had white smoke coming out of my car when I accelerated. I only have white smoke at startup in the morning, so I figure it is condensation burning off. Other then that on low throttle and at idle, it doesn’t smoke.

I checked the radiator and there weren’t any bubbles. I cranked the engine with no plugs in it, and there was no radiator fluid coming out of the holes. So I decided to do a compression check and these were the numbers I got.

#1 #2 #3 #4
135/140 145 145 150

The test was a dry test and the engine had been sitting for about 30 minutes (The time it took to do the water squirting out of the cylinder test, and removal of the spark plugs, and the time it took to find my tools) after I ran the engine around town to get it up to operating Temps.

The #1 cylinder wasn’t consistent, I kept getting either 135 or 140. It was like every other time it would switch. I did the test with the gas to the floor to make sure I got accurate readings.

So actually I have 2 questions…

1) What do you think about the numbers on the test, and did I do the test correctly?
2) If I do a wet test, and the compression raises, does that mean the compression is correct when the car is actually running? I understand that it means the piston rings are bad, but why is that bad? Does that mean oil is getting into the combustion chamber? And if so, then why does it not smoke on idle, or at low RPM’s?

Oh, I forgot to mention the car has approximately 95,000 miles on it. Like most DSM's, driven hard mileage.

Thanks for the help

 

[candela]

1) sounds like you did the test fine... The numbers dont seem to bad IMO. My last motor had like 135 across. Anyway its very close to the service limit of a 2G and you may want to consider doing a rebuild sometime in the future. Were you cranking it the same amount of times? This could have caused any inconsistencies.

2) when cranking and actually running, oil will not help you as far as compression goes. When your cranking the motor is rotating and a tiny fraction of what it does when its actually being loaded and turning high rpm's, not to mention the heat differences. This all translates into less friction which is basically why the oil wont do anything but burn in that condition. Adding a little bit to the cylinders simply coats the rings and (on a car with a higher than limit leakdown percentage on the rings) bumps compression. It tells you a little bit about your condition. Consider doing a leakdown test and seeing where its all going. This should answer all of your questions if done correctly.

 

[SD GST]

Originally posted by candela
1) sounds like you did the test fine... The numbers dont seem to bad IMO. My last motor had like 135 across. Anyway its very close to the service limit of a 2G and you may want to consider doing a rebuild sometime in the future. Were you cranking it the same amount of times? This could have caused any inconsistencies.

I cranked it 5 times on each cyclinder. Any idea why it would inconsitent like that? The other 3 gave the same reading each time.

2) when cranking and actually running, oil will not help you as far as compression goes. When your cranking the motor is rotating and a tiny fraction of what it does when its actually being loaded and turning high rpm's, not to mention the heat differences. This all translates into less friction which is basically why the oil wont do anything but burn in that condition. Adding a little bit to the cylinders simply coats the rings and (on a car with a higher than limit leakdown percentage on the rings) bumps compression. It tells you a little bit about your condition. Consider doing a leakdown test and seeing where its all going. This should answer all of your questions if done correctly.

Assuming that the Piston Rings are fried (Hahah, reminds me of The Fast And Furious) "And the Mad Scientist and I have to rip apart the block," sorry about that... Anyways, if they are fried, how easy is it to replace them. I figure I can replace the head gasket at the same time too. Maybe replace the pistons if I have to take them out when I remove the rings.

I am pretty mechanically inclined, and I do everything on my car myself. I have done headwork before, but never the block. How long of a job is it? I have the air tools and everything, so that will probably make it easier.