Crank case suction and knock

[capri_auto]

Hey everyone,

I bought an 04 disco a couple of years ago with 104k on it. I got it basically for nothing because of some issues and a knock. It has 130k now and all the issues are resolved except for the intermittent knocking. I'm not losing any coolant. I lose about a quart of oil every 1-1500 miles. When I first got the truck it had not one but 2 oil seperators in the valve covers which were very clogged. It was pissing oil due to block pressure at the front cover. I removed both plastic oil seperators. I also had to replace the sai valves and the vacuumed pump also. This resolved the oil leak and ses codes.

So I still get the intermittent knock. I think it may be a clogged oil passage. When the knock is present and loud, I can loosen the oil cap and it goes away. Anytime I remove the oil cap when the truck is running there is a significant amount of suction, is this normal?

 

[KyleT]

What coolant thermostat is on it?

 

[capri_auto]

I put a new oem style t-stat that opens at a lower temp 180 iirc. It has new hoses and water pump too.

 

[KyleT]

Hmm. Maybe run a qt or so of ATF in the oil for a while before the next change.

Have you shot the cooling system with an ir gun to see if it is running 180-200? Reason I ask is I saw 3 trucks do very similiar including my 03 and found the crappy aftermarket stat was not opening and it was running way to hot and cooking the oil. No gauge movement either. New oem 180 start fixed all of them.

Is it burning the oil or leaking it?

 

[seventyfive]

without boring you on partial load, full load, etc. here is what you probably have going on.

you removed the oil separator (which really isn't a true oil separator) which also acts as an orifice. without the oil separator/orifice your manifold is sucking more volume of air now. you need to either put a new oil separator in or take a 1/2" bolt, cut the head off, then bore an 1/8" hole thru it. pull the hose off the plastic hose barb, put the 'orifice' in the hose, put a hose clamp on the hose where the orifice is (to hold the orifice in place), then put the hose back on the plastic barb.

pinch the partial load breather hose (the one at the driver side valve cover to throttle body), start the engine, at idle unscrew the oil filler cap. there should be slight vacuum holding the oil cap when you take it off.

at idle, constant load, and easy transition the manifold vacuum on a D2 is around 20" of mercury so when the oil separator/orifice is removed it is sucking more volume then it should. excessive volume at idle sound almost like a bearing screaming. porsche had this issue on the run of boxsters, the oil separator/pcv sucked so much volume it made the rear main seal whistle!

 

[capri_auto]

Hmm, IIRC my tstat is an aftermarket. It was doing the same thing before I changed the t-stat though, but it's something I will look into. No oil hits the driveway as far as I can tell, but it's going somewhere.

 

[capri_auto]

without boring you on partial load, full load, etc. here is what you probably have going on.

you removed the oil separator (which really isn't a true oil separator) which also acts as an orifice. without the oil separator/orifice your manifold is sucking more volume of air now. you need to either put a new oil separator in or take a 1/2" bolt, cut the head off, then bore an 1/8" hole thru it. pull the hose off the plastic hose barb, put the 'orifice' in the hose, put a hose clamp on the hose where the orifice is (to hold the orifice in place), then put the hose back on the plastic barb.

pinch the partial load breather hose (the one at the driver side valve cover to throttle body), start the engine, at idle unscrew the oil filler cap. there should be slight vacuum holding the oil cap when you take it off.

at idle, constant load, and easy transition the manifold vacuum on a D2 is around 20" of mercury so when the oil separator/orifice is removed it is sucking more volume then it should. excessive volume at idle sound almost like a bearing screaming. porsche had this issue on the run of boxsters, the oil separator/pcv sucked so much volume it made the rear main seal whistle!

Thanks for that info, next time I hear it knock I'll pinch the hose to produce less airflow. For 10 bucks I can just throw another oil separator in. I hope it's that simple. It was knocking when it had 2 clogged separators. I found it strange that there were separators on both valve covers. I though they were only on the passenger side?

 

[seventyfive]

Hmm, IIRC my tstat is an aftermarket. It was doing the same thing before I changed the t-stat though, but it's something I will look into. No oil hits the driveway as far as I can tell, but it's going somewhere.

your consuming more oil due to the higher volume of vacuum on that breather hose, its sucking the oil into the manifold.

 

[seventyfive]

one of the reasons these engines leak so much is the positive pressure.

next time you have your valve covers off or if you have some laying around, take a pozi drive #2 phillips screw driver and remove the baffle plates (inside the valve cover). all the blow by gas and crud turns into sludge and hardens in those baffle plates, which causes the breather tubes to not work properly, then gaskets start to fail and leak because of the excess positive pressure.

not to mention all the oil that is getting sucked into the manifold. ever notice how much oil/sludge is in the plenum? now add a check valve to the partial load breather, install an oil catch can in line to the full load breather and you'll never have to worry about oily sludge in the manifold, plenum, or intake valves.

 

[seventyfive]

fwiw, most engines consume a quart or liter of oil every 1,000-1,500 miles. the newer volkswagen/audi turbo engines consume about a liter every 7-800 miles. personally, every 3,000 miles i have over a pint of oil in my catch can.