Old Faithful? Pressure in the crankcase.

[acme66]

Took the 923 out for a drive tonight, first time it had been driven (some idling and moving it around the yard but nothing on the road) since late fall. About 5 miles out while climbing a hill it lost all power and started stumbling and knocking, like a fuel knock. I was sure it was going to die entirely and just tried to get it off the road before I lost power steering. It never did die but it idled at less than 300 rpm for a bit. Just as I was coming to a halt and reaching for the kill switch it came back to life and seemed to run normally. After inspecting everything I could and pondering the issue some I finally decided that some air had come through, related to sitting for the winter months. Made sense and since it was running normally and had good power (well for a 923 anyway) I carried on with the drive. Nothing seemed to be amiss, gauges normal the only thing I noticed was a light knock, noticeable at idle and again sounding like fuel. I had just about convinced myself some crap had gone through the lines and maybe I had an injector hanging up. Parked it on the apron behind the shop and Dad happened to still be there. On a whim he wanted to hear it. He felt the knock wasn't fuel, thought it was deeper, maybe an exhaust leak. In the process of checking it over he opened the oil fill cap only to have it blown out of his hand. A plume of air and steam pours out. I shut it down sure a head or liner had just let go. When I check the coolant it is fine, no signs of any water in the oil or transmission. It confused us that we could see that level of pressure and vapor in the crankcase but no signs of contamination in the oil or radiator. Pulling the vent line off the valve cover I find that it is plugged where it goes into the intake. Starting the truck we put an old fuel pressure gauge on the vent line and it promptly pegged the gauge at between 6-8 psi, highest that old one read. With the vent line disconnected from the intake there is a steady plume of what looks like water vapor that never stops.

No water in the oil and no strange smell.
No oil in the coolant and no strange smell.
No water in the transmission and no strange smell.
It is not consuming either oil or coolant.
Almost immediately pressurizes the crankcase to over 6psi.
No pressure escaping from the dipstick.
Light knock that may or may not be related to this problem.
Motor never got above 180 at any time during the drive or checking the truck after.
No smoke beyond normal black and a little white from unburned fuel if it idles for a long time. (has always done that)

I would lean towards a compressor leak but where is the water coming from? Why isn't the pressure escaping out the dipstick? Could it simply be condensate from the compressor? Is it blow by from bad rings?

Tomorrow is going to be an interesting day.

Ken

 

[gimpyrobb]

I'd get a different gauge and find out what the pressure truly is. Why not un-plug the vent and run it around the block? Maybe its condensation that just wants out.

 

[acme66]

The amount is so great that at this point I wouldn't want it putting that much water vapor into the intake but maybe pipe it down on to the ground. It seems like so much... the only thing I can think of is a compressor leaking back into the block but I didn't think they shared a connection other than oil lines. Can't seem to picture what the book says right now. I am going to check the 925 in the morning to see what if any pressure it builds in the crank. If it is normal and the 923 still isn't showing oil/water contamination after sitting all night then I might let it run for a bit to see if it clears up. I would also want to know if it is still steaming with the motor dead cold.

Ken

 

[61sleepercab]

Can you do a compression test? How fast(quick) does it start? Sounds like old fashion ring/cylinder blow by? As long as truck starts and you make trips long enough for engine to heat up and boil off any moisture, your engine may be ok. Mark

 

[Tow4]

That's a lot of blow-by. I would do a compression test.

I broke the rings on one cylinder of a gas engine and it did the same thing; lots of blow-by. It was turbo charged and under boost the oil filler cap leaked and eventually the valve cover gaskets started leaking. It ran good with a slight miss.

 

[acme66]

In the morning before I started it I checked the oil and it was a gallon overfull. Coolant in the oil. When it cooled down either the leak opened up or without the motor running the compression couldn't keep the water out. Must be a liner or head. Still not sure if the crank pressure is part of this issue or another. Bummer.

Ken

 

[WillWagner]

Drop the pan and look up the belly. Look at the skirts that are below the liner, (bdc), and look at the liner on the ones that are at the top of the stroke. Look for coolant between the p&l.