Engine trouble- Plummeting oil pressure

-
ro23dart

ro23dart

Well-Known Member
Joined
Jun 13, 2013
Messages
68
Reaction score
6
Location
Harrisonburg
So I took my demon out today to pick up my kid. I had just pulled up to the garage to park it when I noticed it was idling really low, about 500rpm or so almost stalling out. The engine was making some not good noises and the oil pressure had dropped to almost zero. I pulled in and parked it quickly and shut it off. The oil pressure hit about 20psi while pulling it in. It's a 360 with J heads an LD340 intake and 600cfm edelbrock. I've never had the engine apart so I don't know much about the internals. I'm wondering how to proceed. I was planning on draining the oil and cutting open the oil filter to check for metal shavings but once that's done I'm not really sure how to proceed. Hoping to get some info on what else to check and how to proceed diagnosing the problem. Thanks in advance!
 
I'd stick a diagnostic oil pressure gage on it and use a priming shaft to see what the oil pressure does. Probably the two most common issues are oil pump drive failure (tip shears off in the pump) of a bearing problem. Either way the engine needs to come out.
 
Unless for some reason it's really low on oil.
It did climb a little pulling it in.

I'd for sure take a look at that first, as it could have just popped the filter gasket or blow out some other gasket/seal in the bottom somewhere.

Then the filter, and if nothing there either the oil pump drive intermediate shaft.

If no damage there it's at the very least time to pull the pan and have a look at the pump and some lower end bearings.
 
SGBARRACUDA said:
Recent rebuild or existing good engine? Start with the filter.
Click to expand...

It was an existing good engine. Gave me no problems last summer and I've had it out a couple times this summer and it ran fine. Hadn't seen any indications of an issue until today.
 
Great, this gives me a few things to look for first. Thanks! I'll keep you all posted and let you know what I find out.
 
I am curious what oil your using. Have you changed brand or wheight recently? I've had this experience with a couple of my vehicles. I can not run a partial synthetic at all in my 440. The clearance, I believe in the oil pump, won't even pickup the oil in the pan. My 4.7 05 I can run a synthetic but has to be 10-30 or better. I had a local shop change the oil and put in what the cap says, 5-20 I believe, made it 15 miles in dead cold winter. Stopped at buddies house and pressure dropped immediately. Sometimes motors just don't like syn oils.
 
I changed the oil at the beginning of last summer, made a couple of trips and it was all fine.
 
I agree on syn oil, older motors weren't made for that stuff, It's too thin
 
It's just physics.... the lower pressure is a sign of more flow.....really. The pressure sensor pickup is located at the start of the oiling chain so does not tell you what you have way down the oiling chain. A thicker oil will show higher pressure at the gauge, but the pressure drops will be higher all the way down the chain, and you might be shocked to see it be lower down at the mains.

As long as the oil circulates constantly to all parts, you are BETTER off with a synthetic. If you ever had oil system issues and found out how a full synthetic helps things survive sooo much better, you'd be a believer.

Now a pick-up issue IS an issue. But I am having trouble imagining a decent pump not picking up a thin synthetic; it ought to do so more easily in fact. So I suspect a worn pump....
 
My 2 cents, new engines like a 5.7, 6.1 Hemi, LS1, Northstar have very stout blocks and very tight tolerances compared to 340, 440 and older engines. I would not even think of building a 340 with those tolerances, it has to be loose to make power and live. I rebuilt my 71 Cub Cadet Koler cast iron engine and ran Mobil 1 in it, and it gets about 12 to 18 hrs a year running time and it's always against the gov 3600, 3800 RPM . I don't mow much so the grass is always high and has a big load at all times. After 2 years 40 hrs tops the oil did not feel slippery and actually felt sticky, gritty and looks dirty. Changed it out to conventional oil, straight wt and it's been 3 years and it is still slippery and looks clean. You will never convince me that synthetic is for everything.
 
UPDATE 1: So I drained the oil and pulled the valve covers. Nothing weird under the valve covers. The oil did seem less viscous then it should but I'm no expert so I'm not really sure. The thing that did surprise me is that the oil smells like gasoline pretty bad. That leads me to think valve seals or head gasket maybe? Also is there any good way to check the oil for shavings? Maybe running it through some kind of filter? And is there any good way to cut open the filter? Aside from using a tool specifically for that.

It's not synthetic but I will keep that in mind.
 
Gas dilution would do all the things you described. Low pressure and a bad idle. Usually comes from the mechanical fuel pump in the timing cover. Ruptures the diaphragm and spills gas into the pan.

I use a large knife to cut the filter open. Lay the blade behind the rolled edge and hit with a hammer. 4 strikes and it’s off.
 
T56MaxTorq said:
Gas dilution would do all the things you described. Low pressure and a bad idle. Usually comes from the mechanical fuel pump in the timing cover. Ruptures the diaphragm and spills gas into the pan.

I use a large knife to cut the filter open. Lay the blade behind the rolled edge and hit with a hammer. 4 strikes and it’s off.
Click to expand...
must have been typing the same time.
 
Is the oil level on the dip stick way over the full mark? This will let you know how much gas is in the oil pan.
 
ro23dart said:
UPDATE 1: So I drained the oil and pulled the valve covers. Nothing weird under the valve covers. The oil did seem less viscous then it should but I'm no expert so I'm not really sure. The thing that did surprise me is that the oil smells like gasoline pretty bad. That leads me to think valve seals or head gasket maybe? Also is there any good way to check the oil for shavings? Maybe running it through some kind of filter? And is there any good way to cut open the filter? Aside from using a tool specifically for that.

It's not synthetic but I will keep that in mind.
Click to expand...
Check the fuel pump to see if its leaking into the crankcase..and change the needle and seats or adjust the float. Just do it.
 
ro23dart said:
It was slightly over, but it didn't look too overfilled.
Click to expand...
It does not take much gas in the oil to destroy things inside the engine.

Change mechanical fuel pump immediately, no questions asked.

Do the needle & set replacement as said. Then once it is running and idling again, look down the carb throats when idling and see if any liquid droplets are going down the throats; there should be none. And after shutting off, when hot, look to see if there is an fuel dribbling down inside the carb; you ought to open the throttles to look. (Some fuel will squirt from the accelerator pump(s) when you do that; that is not of concern.)

I had to have a /6 block bored .040" over due to damage to the cylinders from slow carb leaks after it was shut off; the PO did not know it was going on.
 
You must log in or register to reply here.
-

Back
Top