Oil Smoke On Steep Descent

I have a 1965 Jeep CJ-5 with an F-134 engine. On 2 occasions I have noticed thick oil smoke coming out of my tail pipe. This only happens when I go down a very steep hill or road and I am letting the engine provide some compression braking to slow my descent. After I get down the steep part and get back on level ground, it smokes like crazy when I get back on the gas and accelerate. The smoke stops within a several seconds once the oil clears out of the system. The engine does not smoke at all when going uphill, level ground or most down hill slopes -- just really steep declines. The engine oil is not over-filled and it does burn much oil.

What are your thoughts on what might be causing this? I don't know where the return oil passages are in the head below the intake valve rocker arms. During steep descents, could the oil that is pumped up to the rocker arms be pooling at the front of the valve cover and not draining back to the crankcase? While the oil is pooled up there, and during hi-vacuum situations, could the oil be getting sucked past one or more bad valve seals into the combustion chambers? Could my PCV valve be malfunctioning when tipped downhill and under hi-vacuum conditions?

Your thoughts are greatly appreciated!

Thank you,
Bob

 

Could be valve guide seals, could be rings.

As you make a long descent, the throttle plate is closed, and you have a prolonged period of high levels of vacuum in your intake. If your guide seals are weak, this could pull air (and oil) past the seals, with the oil accumulating in the combustion chamber until you open the throttle and it then burns off.

The same can happen if the rings are weak. The oil can accumulate on the top side of the rings during low-temp motion (downhill), then when the combustion chambers get hot enough again, the oil will burn off and show as smoke.

 

Seals-----hopefully

 

Thank you for your quick response.

 

Thank you Jeepster Jim. I appreciate your response.

Bob

 

I have seen where an oil bath air cleaner is to full of oil and it can be sucked into the carb.

 

Above info is good. Also, it wouldn't hurt to check and/or clean the PCV valve.

 

Thanks Melvinm. Never thought of that but I will check.

 

Thanks PeteL. I'll check the PCV valve as well. The PCV valve hose connects at the top/front portion of the valve cover. If I was going down a really steep hill, and I did get oil pooling in the front of the valve cover rather than draining back into the crankcase, I might just be possible for the PCV hose to suck some up (if the PCV didn't shut under hi-vacuum). One time this happened to me. I also got oil leaking from the valve cover gasket and the side cover gaskets. I did replace them a year or so ago when I adjusted the valves, but I am not sure that they sealed very well.

 

I will lay my bet on valve guides/valve seals. Your situation is a classic example.
-Donny

 

I second the motion to the above ,tired valve guides and seals need replacing

 

Do f-heads even have valve seals...

Most likely worn guides. Seals can be added to new guides. Valve seats will need work if guides are replaced. By that time you might as well rebuild it good as new.

Is this something that will happen frequently enough to worry about. Or does it compromise safety?
It sounds like a slower decent might be beneficial if the engine is otherwise sound.

 

Intake have o rings and exhaust have nothing.
From the fsm “Defective O-rings could be the major cause of oil leakage into cylinders.”

 

The engine appears to be sound other than this issue.

 

Thank you guys for sharing all your thoughts and knowledge regarding this issue. I think its time to pull my valve cover and see what's going on with my intake valve guides and seals.

 

Pete,

I happened to stumble upon a couple of posts that you had replied to back in 2006 and 2009. In both cases, the problem was someone with an F-134 engine that had oil smoke coming out of the tail pipe. You mentioned that you had seen a case where a malfunctioning dual action vacuum and fuel pump was sucking oil out of the crankcase and into the intake manifold via the vacuum hose. That’s a possibility that I did not think of and will check out.

Also, the first time this happened to me I was driving off-road and climbing up a very steep hill. I parked the Jeep and hiked around for a few hours. When I got back to the Jeep I turned it around and made my way back down the steep trail. That’s when I first noticed it smoking. When I got back to my camp about 20 minutes away, I opened the hood and inspected the engine. There was a lot of oil running down the left side of the engine coming from both the valve cover gasket as well as from the lower engine side cover gasket. I replaced these gaskets about a year earlier and only had very light seepage from them. In this case there was a lot of oil - almost as if the crankcase had become pressurized and was forcing the oil out of these locations. This leads me to believe that maybe my PCV was blocked.

Your thoughts?

Bob

 

You seem to have the general grasp of things in line with my own experiences, with the exception of the "oil pooling" is nothing I've ever heard of in an F-head. If you do find it to be the fuel pump, change your oil in case gas leaked into the sump.

My own 'Flower Power' 1956 is notorious for providing mosquito control on a trail ride I did with members of this group. It smokes on the downhill, especially when you hit the gas afterward. Uses a lot of oil but otherwise it runs fine.

I hope it's just valve guides and/or seals - although I've had more than one F-head where I found busted rings. And one of these days, I may check the PCV...


Back in the day, people used to add devices to do this, called it "Upper Cylinder Lubrication."

 

I like your comment about adding devices for upper cylinder lubrication. A friend of mine inherited his grandfather's circa 1920's Hudson. I had an added device to lubricate the valve train because it had a habit of lacking lubrication in critical areas when going up steep grades.

I am still trying to figure out what may have caused positive pressure in the crankcase and/or valve cover. Some sort of blow-by in conjunction with a clogged PCV system? Or maybe a just had the jeep parked on a side hill and all the oil flowed to the left hand side of the motor.

Going to look into the fuel pump tomorrow. It was a cheap replacement all-metal one (no glass filter bowl). I just sent the original one off to Rick at Old Jeep Carbs to be rebuilt.