What is engine compression telling me?
What is engine compression telling me?
(OP)
Hi,
Sorry if this is an easy question, but I'm not really a good mechanic, so I thought some smart guys here could help me :)
I did a compression test on old Volvo (1998, 2.0, petrol, non-turbo). I did both "Dry" and "Wet" tests (by "Wet" I mean adding a spoonful of oil into the cylinder before measuring).
So, here are the results (cylinders 1-2-3-4):
DRY : 170psi – 170psi – 170psi – 170psi
WET: 170psi – 170psi – 245psi – 170psi
I would understand if cylinder-3 would show low compression on dry, and 170psi on wet test - it would indicate worn rings. But now dry test kinda shows All-OK on all cylinders, but it's way to high on wet test. By the way, manual says the normal pressure is 189-218psi. Yes, 170psi is quite low, but the engine has 190,000 miles on it so I guess it should be expected. On the other hand the manual says 218psi should be the highest pressure on good condition engine, while I get 245psi on an old engine.
I'm a bit baffled here... Anyone has an idea what could be the problem in cylinder-3?
P.S. I did the wet test twice on cylinder-3, and it showed 245, so I'm pretty sure it's not the gauge.
Sorry if this is an easy question, but I'm not really a good mechanic, so I thought some smart guys here could help me :)
I did a compression test on old Volvo (1998, 2.0, petrol, non-turbo). I did both "Dry" and "Wet" tests (by "Wet" I mean adding a spoonful of oil into the cylinder before measuring).
So, here are the results (cylinders 1-2-3-4):
DRY : 170psi – 170psi – 170psi – 170psi
WET: 170psi – 170psi – 245psi – 170psi
I would understand if cylinder-3 would show low compression on dry, and 170psi on wet test - it would indicate worn rings. But now dry test kinda shows All-OK on all cylinders, but it's way to high on wet test. By the way, manual says the normal pressure is 189-218psi. Yes, 170psi is quite low, but the engine has 190,000 miles on it so I guess it should be expected. On the other hand the manual says 218psi should be the highest pressure on good condition engine, while I get 245psi on an old engine.
I'm a bit baffled here... Anyone has an idea what could be the problem in cylinder-3?
P.S. I did the wet test twice on cylinder-3, and it showed 245, so I'm pretty sure it's not the gauge.





RE: What is engine compression telling me?
RE: What is engine compression telling me?
RE: What is engine compression telling me?
The gauge is new, I don't think it's faulty, at least not that inaccurate to show a 30% bigger value, plus I did repeated tests, and this is only happening on cylinder-3...
Maybe it's carbon build-up in cylinder-3 reducing the cylinder volume, hence the bigger compression?
Regarding the compression ratio/pressures, here's what the manual says:
Displacement: 1948 cc
Bore: 83.0 mm
Stroke: 90.0 mm
Compression ratio: 10.5 : 1
Compression pressure: 13 to 15 bar (189 to 218 psi)
RE: What is engine compression telling me?
RE: What is engine compression telling me?
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: What is engine compression telling me?
RE: What is engine compression telling me?
It sounds like an experimental error to me. Even closing the inlet at BDC should not change it that much, especially with a short duration cam as one would expect in an old Volvo as it came from the factory.
Regards
Pat
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RE: What is engine compression telling me?
Mike Halloran
Pembroke Pines, FL, USA
RE: What is engine compression telling me?
I'm planning to use engine "revitalizant" claiming to improve compression in cylinders, and after couple thousand miles I'll repeat the test using teaspoon of oil this time, I'll see if there will be any difference.
RE: What is engine compression telling me?
Regards
Pat
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RE: What is engine compression telling me?
RE: What is engine compression telling me?
I'm trying this because a friend of mine with exact same engine witnessed reduced engine noise/vibration and increased performance/dynamics. I am myself am a big sceptic regarding these products, but my engine is old/high-mileage, so I thought what the hell.. (this is why I measured the compression in the first place, so I can compare later if the claims are at least partially true...).
RE: What is engine compression telling me?
Most likely your oil will become thicker which may reduce oil burning and reduce smoke and reduce noise, oh and reduce engine power and increase fuel consumption, but hey, it's your car and your money.
Regards
Pat
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RE: What is engine compression telling me?
I myself am on your side too, however believe it or not the "revitalizant" claims contrarily - it says it adds ceramic-metal (not metal) and rebuilds worn areas at atomic level using nano-technology. I know, it sounds too good to be true, and I'm sure it won't work so miraculously. However I'm willing to experiment, since the chemical only cost me $100, and I'm not going to rebuild that engine anyway.
RE: What is engine compression telling me?
RE: What is engine compression telling me?
RE: What is engine compression telling me?
Yes it's your money and your engine and you are free to do what ever you want. But do you want the rest of us to know that you have been bilked?
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RE: What is engine compression telling me?
Just run the thing until you get fed up with it, or your wife demands you get a newer car.
B.E.
RE: What is engine compression telling me?
I will know if I have been bilked after the full 3-stage treatment and compression test. As I've said I'm doing this mainly because of curiosity and my friends positive feedback.
P.S. this company sells products in many countries for more than 10 years now, I think they would've been whacked by now...
RE: What is engine compression telling me?
Hm not metal but ceramic metal and at atomic level and nano, it now only needs to be organic and natural to tick every buzzword box.
The point is if it really does plate out on the metal it will do so and wear off all the places you want it to stay, but build up in all the wrong place.
I have a nice bridge for sale.
Regards
Pat
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RE: What is engine compression telling me?
These scams rely on people using them and either "getting positive results" -meaning convincing themselves things are better because that is what they want to believe or seeing no improvement and just absorbing the loss. In the first case the company gets more business from the word-of-mouth endorsement and in the second case they already have your money.
It is not easy to test the effectiveness of a treatment. You need to have multiple trials and you have to carefully eliminate all sources of error. Then, you have to thoroughly analyze results. Finally, your results have to confirmed by other investigators. "I tried it and it worked" doesn't get it.
RE: What is engine compression telling me?
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: What is engine compression telling me?
It might be placebo if I can barely tell any difference in engine performance - this is why I've took baseline compression readings - if it will raise the compression by 15-30psi, make my engine quieter/smoother and stay like this til the next oil change - why the hell not?
I will post the results (no matter good or bad) here, and see I was scammed or not.
RE: What is engine compression telling me?
so cylinder 3's compression increased 170 > 245 psi ywice?
How many revolutions would you say it takes to get the peak reading?
Dan T
RE: What is engine compression telling me?
It takes the same time/revolutions to reach 170psi on all cylinders. On cylinder 3, once 170psi is reached, it stays there for 2-3 revolutions and then jumps to 245.
RE: What is engine compression telling me?
1998, I assume electronic fuel injection was used everywhere by then. Do you disable the fuel injection when doing the comp test? If it has a cold start injector, does it happen to have a cold start injector, and is it located toward the middle of the intake manifold, perhaps a little closer to, or slightly uphill from #3 ?
RE: What is engine compression telling me?
Compression readings before and after use of the engine honey will tell you whether or not that changes things.
RE: What is engine compression telling me?
1998, I assume electronic fuel injection was used everywhere by then. Do you disable the fuel injection when doing the comp test? If it has a cold start injector, does it happen to have a cold start injector, and is it located toward the middle of the intake manifold, perhaps a little closer to, or slightly uphill from #3 ? "
I thought the 245 might be fuel introduce in the cylinder somehow.
RE: What is engine compression telling me?
RE: What is engine compression telling me?
moon161 - I'm not handy or self confident enough to check the valve lash, so I'll leave it for now as engine runs pretty well otherwise. It doesn't consume oil, gas mileage is acceptable. Only as I remember a few years ago the engine ran a little smoother/quieter and had a bit better performance (I reckon it might be because of the reduced compression).
I don't think there is a chance of fuel introduction to the cylinder as I've disabled the fuel pump and injectors.
Fmangas - I'll see what it does - have no feedback yet. I don't want to write the brand of this stuff here (so you guys accuse me I'm the guy from that company advertising it..), but as it says it doesn't change oil viscosity (thin/thicken), the ceramic adheres only to surfaces affected by friction and high temperatures (sounds reasonable so it doesn't build in wrong places like oil passages). - this is what it claims, but I'm sure it can't be that nice.. This is why I bought the stuff costing $100 not $10, so there's a bigger chance it's actually a reasonable product.
RE: What is engine compression telling me?
RE: What is engine compression telling me?
This is a good indication that the engine is due for a valve adjustment, which is a regular maintenance item (for solid lifter models) that needs to be done to ensure maximum performance and engine longevity. I suggest taking it to a mechanic to have this done if you're not comfortable.
RE: What is engine compression telling me?
I suggest learning how to do it yourself. Ideally have someone who has done it before but it is always interesting and fun for engineers to do.
Vital for any motorcyclists or off-roaders that don't ride brand new equipment all the time.
RE: What is engine compression telling me?
Why do you believe this? And why would stuff that costs $100 work better than $10 stuff? If I'm selling a miracle product that doesn't work should I charge $1 or $1,000? This is an interesting question.
I was thinking how would you make something that would actually replace worn away metal and not coat everything it touches. It would have to bind only to "chemically active surfaces" at a molecular level. Surfaces undergoing abrasion are chemically active, however, in an engine, lubrication minimizes this effect, otherwise the parts would bind and gall or wear away very rapidly. So, that won't work well. But if it did, it would be at the molecular level of thickness, in the low nanometer range, not significant at all to replace metal worn away to a depth roughly 10,000 times deeper than that, unless the material will adhere to itself, massively, in which case it will build up, but it would also tend to clump. Not good.
Also, the material needs to be hard or it will be wiped away with the next pass of the rings, so if it does bind to itself and clump, it would tend to make abrasive particles. Not good. There are other problems I can think of.
Now suppose somebody solved all this. All of industry is in need of something so wonderful. It would transform the life expectancy of all manner of machinery. It would be used EVERYWHERE. Is it? If not then probably it doesn't work, except... we know it works at extracting money from hopeful customers.
RE: What is engine compression telling me?
If it is dirt cheap, no one expects it to work. If it's expensive it creates an image of quality and performance.
Regards
Pat
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RE: What is engine compression telling me?
These "plating" products go back a long way, maybe even before autos? Probably before any of us were born. It's not much of a leap to go from coatings, including oils and graphite, etc to the concept of binding a protective layer. Of course it can be done on clean, dry parts, but doing it with an oil additive would be very neat. And then making it actually metallic or something hard and durable, that would be ideal. So, it's an appealing idea like a lot of simple scams.
RE: What is engine compression telling me?
RE: What is engine compression telling me?
Also taking some notice of those who actually know something might be a worthwhile approach.
Regards
Pat
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