compression test - results?

just finished doing a compression test on this motor that ha been sucking water into #3 cylinder.
1-168
2-155
3-195( water in this cylinder )
4-160
i'm wondering why the bad cylinder would have much higher compression.
i'd thought the opposite- much lower if there is a problem in that cylinder.
any ideas?
thanks for the help.

Re: compression test - results?

The water in the cylinder takes up space and raises the compression ratio in that cylinder.
Start the engine for about 5 or 10 seconds without water to it and retry that cylinder. It will probably be down with the rest of them, or lower if damaged by the rust in the cylinder.

Re: compression test - results?

Where do you want the water to go?

I have seen connecting rods twisted cause of water in a cylinder.

The water will compress when the piston moves.

Re: compression test - results?

NO, NO, NO!!!!

The water will compress when the piston moves.

Click to expand...

This is totally wrong!!! Water is NOT compressible!! That's why rods bend and break and come through the side of the block if you try to compress enough water in your cylinder. That's why engines "hydro-lock" when they get water in the cylinders - they can't compress it and it locks up the engine.

If there is just a little tiny bit of water in the cylinder it will take up some space in the cylinder and cause a higher compression reading because IT DOES NOT COMPRESS. It just takes up a little bit of space that would be used by the compressible air, thereby raising your compression ratio in that cylinder (same effect as if you had a domed piston in that cylinder).

This is why Don said to run the motor for 5 or 10 seconds with no water. It will dry out all the cylinders and give you a true indication of their condition when you do the compression test.

Re: compression test - results?

I didn't mean the volume will compress, i have to be crystal clear here.

Think of a soda bottle full with water, with the top on tight.

Squeeze the bottle with a enough force and the water will burst the sides.

Re: compression test - results?

thank you to all for your input into this problem.
i've been told by the manual not to run the motor even for a second without water , but if it has to be done then so be it.

i believe that a worn out water pump is what originally caused all this mess for me . overheated and ran hot for a while.
then next time i ran it i broke the starter when i tried to crank it up after running it on muffs for a while. water filled the cylinder and when i cranked it it broke the stater housing.
i'm hoping the water is just from a leaking manifold, i have it off now and filled with water to see if anything leaks into the exaust ports.
i'm hoping it's not the head or block.
thanks again

Re: compression test - results?

i've been told by the manual not to run the motor even for a second without water , but if it has to be done then so be it.

Click to expand...

Ayuh,....

At this point, with it somewhat Torn down,... Btw, Is the Drive still attached,..??

I'd pull the sparkplugs,+ feed a few tablespoons of Oil into the cylinders,+ turn it over for 30/ 45 seconds, a couple of times....

Just in case there is in fact Water in that cylinder.....

Complete your Compression Test after you put it back together.....

Re: compression test - results?

yes , the drive is still attatched,i,d like to get all this resolved and be able to take out a few more times this year.
thanks for the help!

Re: compression test - results?

Other than a 4 cylinder and compression you gave no information. Year/make/model etc.
If it's an old motor and #3 has water then the riser/manifold is probably bad. To run the motor(Merc/OMC/some Volvos),unhook the water inlet hose at the thermo housing.This way you won't burn up the pump/impeller.Jerry

Re: compression test - results?

i've been told by the manual not to run the motor even for a second without water

Click to expand...

Not sure what you are reading, but to isolate your problems, you need to start that engine and run it without getting water in it.
10 seconds at low rpms is not going to destroy your impeller or your exhaust hoses. It may damage your impeller, but it will not destroy it. But the water in your engine WILL destroy the engine. Your choice. Engine, or impeller. Seems obvious to me. But what do I know.