What is engine compression telling me?

[domaso]

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.

 

[patprimmer]

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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[140Airpower]

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.

 

[dgallup]

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.

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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.

 

[domaso]

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.

 

[Tmoose]

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

 

[domaso]

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.

 

[Tmoose]

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 ?

 

[moon161]

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.

 

[moon161]

"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.

 

[Fmangas]

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.

 

[domaso]

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.

 

[domaso]

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

 

[IBRCAN]

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.

 

[hydroman247]

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.

 

[140Airpower]

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.

 

[patprimmer]

Air

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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[140Airpower]

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.

 

[moon161]

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

 

[patprimmer]

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
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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