Mercruiser 165 Block Pressure Test results confusing

Hello all. Thanks for reading this thread. I know this issue is covered elsewhere in the forum, but I am confused with the results of my block pressure test. I have water in the oil of my engine, a GM 250ci 6cylinder, yet there is no sign of air escaping air when pressurizing the water jacket. I used a soap bubble over the oil cap hole with up to 30 psi into the water jacket with zero distension of the bubble. There is no sound heard with my ear covering the oil fill. I verified pressure in the block by removing the winter drain plug.

Method of test:
1. Drained water jacket.
2. Connected the compressor hose the water intake hose and clamped tightly.
3. Disconnected and plugged hose from thermostat housing to the manifold.
4. Plugged the oil dipstick and PCV holes.
5. Pressurized slowly to 15psi then 30psi.


Could I possibly have a good block or is there a flaw in my testing?
Can water get into the oil via the intake/exhaust manifold or other location?
Is there another place air could be escaping unnoticed?

I will certainly appreciate your thoughts on this.

Thanks!

Re: Mercruiser 165 Block Pressure Test results confusing

did you remove the sparkplugs first and listen with a small hose to your ear?

Re: Mercruiser 165 Block Pressure Test results confusing

Bt Doctur said:

did you remove the sparkplugs first and listen with a small hose to your ear?

Click to expand...

As per your suggestion, I just now tested as above and heard nothing. I also used the soap bubble test over each plug hole and all passed. No leakage.

Re: Mercruiser 165 Block Pressure Test results confusing

998cc said:

Hello all. Thanks for reading this thread. I know this issue is covered elsewhere in the forum, but I am confused with the results of my block pressure test. I have water in the oil of my engine, a GM 250ci 6cylinder, yet there is no sign of air escaping air when pressurizing the water jacket. I used a soap bubble over the oil cap hole with up to 30 psi into the water jacket with zero distension of the bubble. There is no sound heard with my ear covering the oil fill. I verified pressure in the block by removing the winter drain plug.

Method of test:
1. Drained water jacket.
2. Connected the compressor hose the water intake hose and clamped tightly.
3. Disconnected and plugged hose from thermostat housing to the manifold.
4. Plugged the oil dipstick and PCV holes.
5. Pressurized slowly to 15psi then 30psi.


Could I possibly have a good block or is there a flaw in my testing?
Can water get into the oil via the intake/exhaust manifold or other location?
Is there another place air could be escaping unnoticed?

I will certainly appreciate your thoughts on this.

Thanks!

Click to expand...

Ayuh,.... The Idea is to block off the Water passages, 'n open up all the other holes to listen through,...

Spark plugs out, dipstick out, vent open, etc....

How much water were ya gettin' in the oil,..??

Re: Mercruiser 165 Block Pressure Test results confusing

Bond-o said:

Ayuh,.... The Idea is to block off the Water passages, 'n open up all the other holes to listen through,...

Spark plugs out, dipstick out, vent open, etc....

How much water were ya gettin' in the oil,..??

Click to expand...

WIth hindsight, I should have stated earlier that this is a new-to-me boat. The oil was clear when I bought it, so I didn't think to check for excess level. After starting and running the engine about 20 minutes, I checked and found the milky oil. It has about a quart or a little more excess fluid in the crankcase. Could the water be from another source? The ignition coil was bad, and the dsitributor internals were pretty well corroded, so I assume the engine had been exposed to weather.

Re: Mercruiser 165 Block Pressure Test results confusing

I checked and found the milky oil. It has about a quart or a little more excess fluid in the crankcase. Could the water be from another source?

Click to expand...

Ayuh,.... The Water, will be Under the oil,.... Did ya try drainin' a sample outa the base,..??

Is the milkiness in the valve cover at the oil fill, or on the dipstick as well,..??

Re: Mercruiser 165 Block Pressure Test results confusing

Bond-o said:

Ayuh,.... The Water, will be Under the oil,.... Did ya try drainin' a sample outa the base,..??

Is the milkiness in the valve cover at the oil fill, or on the dipstick as well,..??

Click to expand...

No sample was taken, and yes, I agree with the notion that there was likely a pool of water under the oil which later mixed as soon as the engine started. There is definitely milky sludge on the dipstick now. This is not just condensation from normal combustion. I am thinking the block may be OK and bought oil and filters today for two changes. Maybe change the oil, run for 20-30 minutes or so to flush out the remaining water-oil sludge and change the oil again and run for another 30 minutes or so then recheck the oil. I guess that is the only way to truly tell.

Thanks!
998cc

Re: Mercruiser 165 Block Pressure Test results confusing

998cc said:

No sample was taken, and yes, I agree with the notion that there was likely a pool of water under the oil which later mixed as soon as the engine started. There is definitely milky sludge on the dipstick now. This is not just condensation from normal combustion. I am thinking the block may be OK and bought oil and filters today for two changes. Maybe change the oil, run for 20-30 minutes or so to flush out the remaining water-oil sludge and change the oil again and run for another 30 minutes or so then recheck the oil. I guess that is the only way to truly tell.

Thanks!
998cc

Click to expand...

Ayuh,.... Rather than wastin' the oil,...

Drop what's in it, 'n change the oil, 'n filter,...
Then Run it....

If the Level ain't Risin',..

Run it Hard enough to build heat, 'n Steam it out....

Re: Mercruiser 165 Block Pressure Test results confusing

I would do just that, but the out drive needs at least the maintenance items such as new bellows, shift cable, etc. I wanted to be sure the engine was sound before pouring any money into the out drive. I did, however, pick up another complete Mercruiser 250 6 engine, mounts, gimble, out drive, etc., plus another upper out drive in a package deal. The plan is to start the "new" engine Sunday to see what condition it is in before taking any further steps with either one.

Re: Mercruiser 165 Block Pressure Test results confusing

If anyone is interested, cylinders 5 and 6 of the "new-to-me" engine had been exposed to rainwater through the open exhaust manifold which resulted in leaky valve seats, so no preliminary start-up took place. I tore it down, Gunked and pressure washed the block and can see no visible signs of cracking. The engine had been previously bored .030" over, and the crankshaft is .010" undersize. Since there is almost no piston wear and almost no ridge at the tops of the cylinders, the plan is to just hone/re-ring, install new rod, main bearings and freeze plugs. Will mic and touch up the valve faces/sets on the other head and use it.

Thanks for all the input gentlemen.
998cc

Re: Mercruiser 165 Block Pressure Test results confusing

Update: After running the engine for about an hour yesterday, there is no sign of water in the oil, so it looks like the block is good. The boat project has new life! Now to the stern drive.

Russ

Re: Mercruiser 165 Block Pressure Test results confusing

Glad to hear! :joyous: