Pressure Testing an Engine

[cabot24]

Good Day All...

I am working on my '06 Mercruiser 3.0L.

Let say I find this forum extremely valuable and often VERY informative.

While changing the oil in our party barge I noted the dreaded WATER IN THE OIL, not much.... but not much is still some.

That said I have read a great many articles on the site relating to Water in Oil. While is suspect the odds are not in my favor I want to ensure I have explored all options. It seems the next logical step is to conduct a pressure test on cooling system to check for cracks. Finally manage to find a post that describes the basics of how to perform the test but have yet to find one that provides specifics. Specifics, such as how much pressure to apply, and how long the pressure should hold in order to qualify as "good" or more than likely not cracked

So here is where I am at...

1) Removed the fresh water intake hose and attached a small pressure pump with a gauge installed to the thermostat housing.
2) Removed the thermostat housing to manifold hose and attached a short hose / pvc cap to plug up the return side.
3) This should have created a closed system.
4) I then pressurized the block to 10 psi, no drop in pressure was noted when I checked about a half hour later.
5) I gave another quick check the next morning, pressure had fallen off to about 5-6 psi.

I can point to any number of components that could account for a slow leak in this test, and before I go chasing them down I am just trying to confirm I am doing this correct. So I am looking for a little advice, what am I missing, or am I doing this right. Any other recommended nest steps.

THANKS IN ADVANCE ALL.

Brian

 

[998cc]

Re: Pressure Testing an Engine

Hello Brian. A few thoughts: I just went through this on my 4.1 (GM) 250 inline 6. How much water was in the oil? A tablespoon, a cup, a quart or more? A small amount of water in the oil could be condensation from running the engine for short periods and not allowing it to warm up sufficiently to evaporate what had condensed/collected in the crankcase.
1. From what you describe, it sounds like your block *may* be holding pressure. To test my block, I blew the remaining water out of the water jacket and plugged off any water outlets that would be pressurized. I made up a hose to connect to an air compressor and pressurized the block to 15+ PSI (as is suggested elsewhere in the forums). I then plugged off the oil dipstick tube (perhaps other crankcase openings on your motor) and using a soapy water solution, created a "bubble" across the oil fill hole and watched for changes in the bubble. You could do the same for each spark plug hole.

Curiously, when the block was pressurized, a leaky water pump gasket was found by spraying the soap solution on the outside of the engine using an old Windex bottle.

2. On the other hand, if the amount of water was minute, you may just want to change the oil and go boating while assuring the engine warms up properly. Check the oil for the proverbial "milkshake" during the outing.

 

[cabot24]

Re: Pressure Testing an Engine

Good morning and thanks for the reply...

To add a missing detail or two...

The Water in the Oil was enough to slightly "Milkshake" it once in the pan it did manage to separate and the volume of water was well more than condensation but certainly not pints.

I have taken off the handy mercruiser block drain quick release and plugged directly at the block. Since I have read on here that the 3.0 tends to crack near the oil pump inside the pan I have pulled the dipstick and covered the hole with a balloon to check for a leak under there. Changed my rig to pressurize via compressor and re-press to 20 psi. Stayed with the block and routinely sprayed a soapy solution for nearly an hour. No visible bubbles, no hissing sounds, balloon didn't inflate.

So back to my original questions, any suggestions as to how long to run the test, what pressure to use, and what is considered a "good" result, holding 20 for an hour???

So if the block is deemed "Good" what would the next recommendations be?

Thanks in advance.

Brian

 

[smassey22180]

Re: Pressure Testing an Engine

If it were my 3.0, and I own a 3.0, I would change the oil and see if it comes back. It could be several other odd ball things not related to the block/head. Some people get water in the engine from an issue with the exhaust. Many years ago we had a car that would milkshake its oil after 6 months. We changed the oil every 3 months for the next 3 years and the car lasted to well over 300k miles

 

[Eric 3.7LX Alpha 1]

Re: Pressure Testing an Engine

Temperature effects PSI.. meaning, if you pressure test and it's 90?F, and check it in the morning when it's 75?, there is a great chance the gauge will read lower... and vise versa just from the change in temperature.

The smaller graduations on the psi gauge the better also.. if you are using a 100 or 200 psi gauge to test at 20 psi, it's not going to show as well as a gauge that reads a max pressure of 30 psi.