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What is engine compression telling me?

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.

RE: What is engine compression telling me?

(OP)
One more thing - when testing cylinder-3, the compression seems to be the same (170) for a while, but after a few additional turns it jumps to 245.

RE: What is engine compression telling me?

I would say you are worrying needlessly. Look at it from the other direction. Having even pressure across all four cylinders is a strong indication nothing is wrong. And to have 170 psi I would think is excellent..... so excellent that I might question the accuracy of your gauage. At normal atmospheric pressure of 14.7, a reading of 145 -150 psi implies a compression ration of about 10:1. Is you engine really set up with 11.5 :1 compresion pistons?? The 245 reading is an anamoly. Leave it at that.

RE: What is engine compression telling me?

(OP)
245 also seems unreal to 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?

Most likely you added too much oil to that one cylinder.

RE: What is engine compression telling me?

Assuming there are no errors in your method, the variation you are seeing in cyl 3 is very odd. It makes me wonder if there is an intake valve timing (i.e. early closing) issue that comes and goes.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: What is engine compression telling me?

(OP)
Could be.. But wouldn't it cause higher pressure on dry test too?

RE: What is engine compression telling me?

Not if it comes and goes and was gone when you did the dry test.

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?

The wet test spoon should be a teaspoon, not a tablespoon.

Mike Halloran
Pembroke Pines, FL, USA

RE: What is engine compression telling me?

(OP)
I've must've added too much oil then.. However I still don't think it would have caused 30% higher reading...
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?

oooooh, mechanic in a can...

RE: What is engine compression telling me?

(OP)
noooope, mechanic in a TUBE... :)
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?

No additive can put metal back into the bores or rings. Your piston to bore will not decrease, your bores will not miraculously become straight and round, your ring end gaps will not decrease and your ring side clearance in the pistons will not decrease.

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?

(OP)
"No additive can put metal back into the bores or rings. <...>"
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?

I'd repeat the compression test for a baseline.



RE: What is engine compression telling me?

(OP)
Well, I already did the test twice (same results), but I guess it won't take long to do it one more time just before the first stage of revitalizant treatment.

RE: What is engine compression telling me?

Only $100! What a waste. The FTC comes along and whacks these guys with a cease and desist order and some small fine every once in a while but there are a dozen scam artists waiting to take their place.

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?

----------------------------------------

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?

When I sold my Volvo Station wagon it had 450,000 miles on it and the compression was about 165psi on all four cylinders. It was still running well.
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?

(OP)
Call me whatever you like... I don't feel bilked as $70 is engine oil with stage-1 revitalizant (I needed an oil change anyway), remaining $30 is two tubes of revitalizant for stage-2 and stage-3.

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?

Ya think.

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?

What Pat says is profoundly true. If the stuff actually did "bind to the metal" it would do so in the wrong places, the places not being wiped by contact with other parts like the sump, heads, oil passages, etc.

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?

Placebo effect. And not wanting to admit that you've been somebodies mark. A lot of seniors who have been conned out of their life savings will deny that they have been fooled.

----------------------------------------

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?

(OP)
Guys, I agree with all of you. Why can't you understand that this is just an experiment...
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?

Hi Domaso,

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?

(OP)
Hi Tmoose,

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?

The 245 jump only occurs during a wet test? Do you block the throttle open?
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?

Tight valves, or carboned up or worn valve seats can also give you a low compression reading. Making sure that the valve lash (rocker clearance to cam surface)is properly adjusted. Though there are opportunities for an expensive mistake, this is a nice get your hands dirty experience that is not too hard. The 245 PSI is strange, but unless the engine runs badly, and uses a huge amount of oil through crankcase blow-by, or has horrible power or mileage, you dont have a problem worth solving by replacing the rings and honing the bores or a more extensive rebuild. The even readings indicate that the engine should run smoothly.

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?

"The 245 jump only occurs during a wet test? Do you block the throttle open?
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?

Be careful using this type of additive. Part of there process is to use a bit of solvent in there mix to help it get "bite into the rings and bearings" This solvent can thin your oil with catastrophic effects. I know from trying the same experiment after a friend raved about the product. I drove 5 miles and wiped all the rod and main bearings on a perfectly good high milage engine.

RE: What is engine compression telling me?

(OP)
Tmoose - before doing the test I've disabled the ignition coils, fuel pump, and fuel injectors. However, after you've mentioned, I remembered I forgot to tell by brother to keep the accelerator slammed to the floor when turning the starter motor.. So I know realize my readings are with closed throttle... But I guess it sucked the air via one of the manifold-airfilter hoses or idle air control valve.

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?

(OP)
Tmoose - yes, the 245 jump only occurs during the wet test.

RE: What is engine compression telling me?

Quote (domaso)

Only as I remember a few years ago the engine ran a little smoother/quieter and had a bit better performance

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?

Quote (IBRCAN)

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.

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?

domaso, you said " 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)"

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?

You are right Pat, Pricing is an art and a science. It depends on what you are trying to sell and to what type of customer. I remember being intrigued by the possibility that a plating product being advertised, like this one, might actually work. This was about 40 years ago. I finally concluded it couldn't possibly work. If I was naive I might have tried it... at $20 a pop in today's money, but not $100.
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?

As gateway drugs go, valve job is a good one.

RE: What is engine compression telling me?

A properly done compression test with results that are actually possible would be a good starting point to sort this out.

Also taking some notice of those who actually know something might be a worthwhile approach.

Regards
Pat
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