1991 4.6 engine (valve seal problem)

[bluesboyst]

I have a 1991 Town Car with a 4.6 engine. When I am stopped and the car is idling for a while a puff of smoke comes out when I accelerate. No smoke comes out when I am going. I am told that the 4.6 engines have a problem with valve seals wearing out. Is this job worth having done. Will it stop the oil from burning? The car still runs like new.

[This message has been edited by bluesboyst (edited December 31, 2000).]

[Lscman]

It's hard to say whether it's a mixture rich tip-in condition or oil sucked thru the guides. If it blows a cloud when it's started up cold and it dissipates quickly, it's probably the seals. If not, it's probably fuel mixture. Does the car use excessive oil? I don't know too much about servicing the overhead cam heads, but my guess is replacing valve seals is very expensive. I've never heard that rumor about seals going bad prematurely. How many miles on it??

[bluesboyst]

It does not blow smoke when I first start the car in the morning. It has 115,000. It uses about a quart every 600-700 miles. I talked with someone who had it done on the same car with 110,000 and it stopped the oil burning. I just want to see if anyone else had this problem. At the dealer it is about 1000.00 for the job...

Thanks

[Wojo]

My 91 Towncar does the same thing, but it has 165K on the engine. I bought it with 145K and it has been doing this since I bought it. It hasn't gotten any worse. Messing with the PCV system has helped some. But if it idles for a long time it smokes alot. When I follow my wife when shes driving it I notice that is puts out a very small puff when she lets up on the gas. I looked at the plugs when I changed them and there was no evidence of burning oil on them. 20+ thousand miles should have shown a bunch of residue but they looked almost new. If you look at the ford engines, you will see that the oil drain holes are located such that the oil level will come up to the exhaust valve stems but never to the intake valves. So my theory is that the oil runs down the exhaust valve stems and gets burnt by the super hot exhaust gasses while you are driving, thus creating little or no smoke and never enters the comubustion chamber. FYI FOMOCO does not consider oil usage of 750 mi / QT as excessive (see any ford manual). Therfore even if it was new they would not do anything to correct this type of consumption. If you get emission checked you will eventually have to correct this or get waivered otherwise I would just add a QT whenever.

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'59 Edsel Ranger
'72 LTD Ragtop 400
'89 MKVII LSC
'90 MKVII LSC
'91 Towncar
'95 Silverado????

[Lscman]

Oil consumption in the 800 mi/qt range is not unusual and that's with no drips/leaks. In general, the "classic" problem with valve stem seals is intake vaccuum sucking oil past the intake stem seals. They must be good. This usually causes a puff of smoke when starting or letting off the gas to go down hill or slow down. The symptoms you describe for smoking don't fit this pattern, though. The seals on the exhaust valves see positive exhaust pressures, more with increased engine loading and tend to not let oil seep in, even with bad seals. Catalytic converters tend to mask the problem and make it difficult to diagnose. Wojo's theory may be more accurate, but my guess is the high voltage ignition and combustion temps of a SOHC motor would keep the spark plugs fairly clean, even with oil being burned.

[bluesboyst]

The plugs on my car also are fine when I inspect them.

Thanks

Steve

[Richard J. Parker]

From epinions.com on 92 TC with 100k:

"The engine likes to eat oil. There's no visible smoke and it passes the strict NJ smog test. I managed to drop oil consumption down to about 1qt. between changes by using Castrol syntec 5w50"