Losing oil and I don't know why

[stang1986gt]

My truck is a 67 with a cammed 302. When I got it I noticed someone had blocked off the pcv valve with a hose and bolt and closed off the connection on the base of the carb. So I drove it 3 1/2 hours home from Columbus and it did great other than some oil blowing out of the breather on the driver side valve cover. The oil level didn't really go down much on the trip home. I cleaned it up and hooked the pcv valve (valve is fine and not stuck) to the carb base and all seemed well. Checked oil, topped it off and forgot about it. Drove it about three times to work 24 miles round trip each way. Then to a cruise in about 20 miles away. Checked the oil and it was 1 1/2 quarts low! Filled it up and drove it three more times. Checked it again and it was another quart low. The truck runs great and doesn't smoke other than just a little when you first start it up. Any ideas? My breather is a little gummed up and I need to replace it. It's not leaking that much oil either. It does leak slightly but not much. How could I be losing this much oil and it not smoke like a freight train? It's not putting oil out the exhaust either. Kind of stumped.

[71Fe2O3]

That is vexing. I am wondering why and when the previous owner plugged up the PCV system, and why that didn't cause more leakage out the valve cover, oil pan or rear main seal on your way home-you would expect that engine, unless it was recently rebuilt, to have significant blow-by, and it has to go somewhere.

You might be losing oil in a way that is hard to detect if the leak is from a pressurized part of the oil delivery plumbing-the oil filter comes to mind. If this is the case, the oil leak would be most significant when the engine is under load and the volume being pumped is highest, coating the road under the truck as you go along but leaking much less when the engine is idling or off. You may also have some gaskets that were weakened as a result of the plugged PCV system, for example the oil pan gasket, that allow oil to slosh out while you are driving. It may not be very noticeable if it doesn't leak onto the exhaust manifold or head pipe. Do you find oil on the transmission or the underside of the truck?

Your question brings to mind an oil leak in my Subaru that did this-in this case it was from an oil pressure switch and associated solenoid on one of the heads, a system the the trucks don't have, but the point is that it only leaked when the engine was under load, resulted in significant oil loss (I referred to the car as the Subaru Valdez during that time,) and took me a while to figure out because I was unaware of that system and therefore looking elsewhere. Fortunately, the trucks have much simpler oil delivery systems, so you will likely solve your problem pretty quickly.

[stang1986gt]

That is vexing. I am wondering why and when the previous owner plugged up the PCV system, and why that didn't cause more leakage out the valve cover, oil pan or rear main seal on your way home-you would expect that engine, unless it was recently rebuilt, to have significant blow-by, and it has to go somewhere.

You might be losing oil in a way that is hard to detect if the leak is from a pressurized part of the oil delivery plumbing-the oil filter comes to mind. If this is the case, the oil leak would be most significant when the engine is under load and the volume being pumped is highest, coating the road under the truck as you go along but leaking much less when the engine is idling or off. You may also have some gaskets that were weakened as a result of the plugged PCV system, for example the oil pan gasket, that allow oil to slosh out while you are driving. It may not be very noticeable if it doesn't leak onto the exhaust manifold or head pipe. Do you find oil on the transmission or the underside of the truck?

Your question brings to mind an oil leak in my Subaru that did this-in this case it was from an oil pressure switch and associated solenoid on one of the heads, a system the the trucks don't have, but the point is that it only leaked when the engine was under load, resulted in significant oil loss (I referred to the car as the Subaru Valdez during that time,) and took me a while to figure out because I was unaware of that system and therefore looking elsewhere. Fortunately, the trucks have much simpler oil delivery systems, so you will likely solve your problem pretty quickly.

When I looked under the truck before I got it, there is some oil but nothing to be concerned about. When I noticed a couple of weeks ago that oil was going down, I looked under again and there's no change in the amount of oil. It's not spraying back through the underside of the truck while I'm driving or anything. In fact when I park at work for 8 hours, I always check for oil leaks on my old cars and trucks (work parking lot is concrete...parking spot at home is gravel ) and there's never any oil under the truck.

Here's what I think is happening. Someone put cheap chrome valve covers on the engine. And while I haven't checked to make certain, I don't believe there are baffles in the covers. So when hooked up, the PCV valve is sucking oil out and it's getting burned while I'm driving. This wouldn't create noticeable blue smoke. Also I believe the valve seals need to be replaced. I think it's a combination of the two.

I plan to check to see if the covers have baffles, and if not, I'll replace those. Also I'll pull the plugs to see what they look like and do a quick compression test on the engine to see if the numbers are the same across all 8 cylinders. I'll report back when I get a chance to do this.

[markguiver]

The 390 in my truck was experiencing the same symptoms as yours for the last few years. Using oil, a couple of small leaks, blue smoke at startup, etc.. . The motor has around 30,000 miles on it, has good compression numbers, and really had no reason to be doing this. A couple of months ago I pushed it too far and ran out of gas about a mile from home. No big deal, just walked home (in the rain of course), got a five gallon can of gas walked back and poured it in. I had the air cleaner off and when I got the truck started I was hooking the air cleaner back up, which has for years had the fresh air intake for the PCV plumbed into the bottom of the housing. When I hooked the tube for the fresh air intake back into the air cleaner the idle RPM's dropped by at least 200 RPM's. I realized the vacuum from the fresh air intake for the PCV system was pulling combustion air out of the intake manifold. Living at 8,500 ft. I need as much air as I can get into the engine so I figured some changes to the PCV system were needed. I am not a big fan of the OEM vented oil filler caps with the mesh screen filter due to daily dusty dirt road driving. I put one of the K&N pleated filter caps on the valve cover and put a new PCV valve in the other side (passenger) valve cover. I also put an oil/air separator between the PCV valve and the carb to keep oil from getting sucked into the intake manifold. What a huge difference! The small oil leaks are gone, the truck runs better and starts immediately with the turn of the key , and the motor quit drinking oil. The air/oil separator gets a little oil in the reservoir so that isn't getting in the intake manifold and leaving deposits in the intake system. I also use an additive at each oil change to add zinc to the oil. I will also add that I run the stock valve covers, an OEM 4 barrel intake (S) with an Edelbrock 1406 carb that's jetted for this altitude. The properly functioning PCV system, as well as all the fuel system mods to stop the vapor lock has made it a pleasure to drive the truck again.
Mark.

[colnago]

I realized the vacuum from the fresh air intake for the PCV system was pulling combustion air out of the intake manifold.

I don't understand this statement (or maybe my brain is parsing it backwards). How is it pulling combustion air OUT of the intake manifold? The intake should be sucking air out of the crankcase via the PCV.

Joseph

[markguiver]

I realized the vacuum from the fresh air intake for the PCV system was pulling combustion air out of the intake manifold.

I don't understand this statement (or maybe my brain is parsing it backwards). How is it pulling combustion air OUT of the intake manifold? The intake should be sucking air out of the crankcase via the PCV.

Joseph

The air being sucked thru the PCV valve is pulled into the engine from the breather on the valve cover on the other side. On most of the Ford engines in the era the breather was/is on the left (driver) side and the PCV valve was/is on the right (passenger) side. As the vacuum pulls the air through the PCV into the intake manifold the breather supplies fresh air to be drawn through the engine. The way I had my engine breather plumbed, which was underneath the air filter housing (Edelbrock 14" drop base) the breather was pulling filtered air into the engine. The carb and the engine breather were basically competing for the same air. Now each of them have their own filtered source of air supply so the carb can take as much as it can in the thin air here. Sure works better now since I changed it back to the way it was designed back when it was new.
It could have been the way I worded it and I hope this clears up your question.
Mark.

[colnago]

Mark,

Thanks for the clarification. I also did some "googling" this afternoon, so I think I have a much better understanding of the whole PCV system now.

stang,

Any progress on your issue? When I bought my truck, the PO had removed the PCV valve, and I just had two breathers. This was great for relieving pressure, but I had condensation build up in the crankcase. Once I reconnected the PCV back up, the condensation disappeared.

Joseph

[colnago]

Oops! Double post!

Joseph

[stang1986gt]

I checked the valve covers this evening and there are no baffles on either side. I can touch the tops of the rocker arms.

[markguiver]

I checked the valve covers this evening and there are no baffles on either side. I can touch the tops of the rocker arms.

Maybe that's the reason the PO pulled the PCV valve out. If oil was squirting onto the valve and being sucked into the intake that would maybe cause it to smoke as well as us more oil. It's hard to try and figure out why PO's do some of the things they do. I would definitely replace the valve covers with baffled ones, then get the PCV system functional which may stop or at least slow down the leaks/oil consumption.
Mark.

[stang1986gt]

Yea, that's what I'm thinking. If the truck doesn't sell this weekend at the swap meet I'll start saving some money into investing into new valve covers. I have a good bit of room before I start losing money I guess. I'm afraid I'll get all the little things fixed and want to keep the truck!

[colnago]

I'm afraid I'll get all the little things fixed and want to keep the truck!

But that's a good thing!

Joseph