I am having a problem on a 1987 24 ft Class C motorhome. It is a ford 460 with a 4bbl. It has 36K miles on it. I am experiencing high oil consumption ~ 1 qt per 100-250 miles. A shop did some diagnostic work and was unable to determine the problem.

-Huge blue smoke cloud after reapplying throttle after periods of high vacuum on engine (mainly after coasting down hill)
-Cloud of smoke seems to somewhat related to making turns to the left. Another person with a 460 in a Lincoln had this exact symptom in another newsgroup post.
-Only one spark plug carbon fouled. (Not sure which one, I did not do the work)
-Compression and leak down check had excellent results.
-No oil in the air cleaner
-Replaced PCV valve
-Driver side valve cover removed. Engine is as clean as a pin
-#8 cylinder valve stem seals replaced. They were soft. Originally thought I had a stem seal problem. Mechanic stopped after seals were found soft. I am not sure if this was the cylinder with the carboned up plug.
-No blue smoke on startup after sitting (long and short periods)
-Engine runs a little rough on idle
-Engine stumbles or runs rough up from idle
-Fresh tune-up (plugs,wires,cap,rotar)
-Mechanic though I might have a leak between carburetor and EGR plate (unrelated to smoking problem)
-Ran some motor flush and switched to straight 40 weight oil. No improvement
-Seems to be temperature related. The hotter the engine gets the worse it gets
-Very slight wisps of smoke from exhaust pipe at idle when engine is hot (up to normal temp)
-Engine runs well
-Slight oil leak from the backside of the intake manifold.
-Previous owner pulled a heavy trailer on occasion
-Rear end ratio is 355
-Cooling system performs adequate

I am leaning towards an intake manifold leak at a runner. I am thinking I could be sucking oil from the lifter galley. This is based on doing a lot of reading on the net. Any recommendations on someone I should call who has a lot of experience with older 460s. Please help

 

have the cooling system pressure tested or do it yourself if you lose pressure you may have a bad headgasket

 

I just got my motorhome back from the shop. It was the intake manifold leaking. It was leaking on the right passenger side bank, #2 cylinder. The valley pan was full of oil. When I would turn left the oil would slosh to the right and get sucked in. The valley pan was distorted from vacuum on the right side. This let oil get on top of the valley pan. The shop had never seen this in 40 years. I have been out test driving. No smoke and it idles and runs smooth now. Hopefully it won't leak again. Nothing appeared to be warped or cracked.

Thanks for everyones help.

Mike