Compression Test Passed - What does this mean?

It means that the head gasket is probably not a problem right now. They put a pressure gauge in place of each spark plug. Then they crank the engine over and see how much pressure is generated in each cylinder. If the gasket has failed, you will not get as much compression in one or more of the cylinders. I would ask them how much compression each cyl was producing. It should be something like 100-120psi in each cylinder. As long as they are all about the same you should be fine.

It means that they took a pressure measurement of the compression generated by the pistons traveling up the cylinders. A pass indicates that the pressures are within the manufacturer's tolerances for engine wear or damage and that most importantly the different cylinders were within 5% of each other indicating the engine in is a consistent state.

That says with a reasonable degree of certainty that:

1) The head gasket is sealed

2) The cylinder walls are not cracked

3) The cylinder head is not cracked around the compression chambers (read on though)

4) The pistons and rings are in a serviceable condition

5) The inlet and exhaust valves in the cylinder head are in a serviceable condition

There are other types of leaks and cracks that are not detected by a compression test. In your case you probably have a leak between the water jackets and oil jackets that is not affecting the cylinders and therefore compression. I assume that the head gasket was recently replaced given that you had previous trouble. Therefore sadly I predict that either the cylinder head is cracked or corroded between the oil and water jackets (likely) or that the engine block is cracked between the oil and water jackets (unlikely) or that head gasket is still not sealed due to poor fitting or warped cylinder head (possible if the mechanic is incompetent)

Any way you look at it this is not good news sorry.

teef_au

Head Compression Test

Did they not do a block check (sniff test)? They should've put this into the coolant resivoir to check for combustion gases in the coolant. The block checker uses a blue liquid that turns yellow/green if the gasket has failed. This needs doing and it only takes a couple of minutes.

The emulsified oil on the oil filler cap will occur if used on short journeys where the engine doesn't warn up enough.

One other thing, never put cold water into a hot engine when the coolant resivoir is empty. It will do the engine no favours at all.

If you're still seeing steam out of the exhaust when fully warmed up (it will in cold temperatures until driven a few miles) then I'd still be concerned about head gasket failure or EGR valve gasket.

Cylinder is done through the plug holes water is done through the radiator.

Detects any leaks

Water in the oil is not good

Head gasket will cause this but will not show in a compression test.

Head gaskets separate water and oil in joining parts Eg head and block.

Faults in the head or even incorrectly fitted gasket can cause this to happen.

This doesn't normally affect the running of the engine but that doesn't mean drive it because it can do a lot of damage.

Speak to who ever done it in the first place.

If you have NOT been using synthetic oil, have the oil flushed and changed and begin using it now!! Sometimes excessive moisture in the crankcase (making goo) is due to poorly adjusted fuel mixture or a leak in the PCV valve and/or hose. It also can be due to a lazy mechanic, that hasn't removed dirt form the parts he intends to re-assemble with the head gasket issue. Clean out your throttle body and idle air control valve with Gum-out. Make certain that there are no leaks in the intake gasket seal. Good Luck!!

It means your cylinders are good and head gasket also. If you do a compression test and your cylinders numbers are diferent by 10 or so psi you have problems with that cylinder, meaning your piston rings are worn. You could also have cracked block or water jacket, because sounds like your getting antifreeze in your oil.

It means that your car has no air leaks throughout the combustable chambers and manifold. If you had even a hair-line crack in any gaskets or seals, then your car would've failed the compression test.

A private sale is assumed to be "as-is" unless there is something in writing to the contrary. You should have had the car checked out prior to purchase. You now will have to pay for the repairs, or sell the car to someone else!

It's similar to a cylinder "leak down" test and is one indication of a healthy engine.

http://www.mobil1.com/USA-English/MotorOil/Car_Car...