Consumption is inconsistent by driver

[jorton]

98 f150 4.6 V8
Coworkers truck consumes one quart every 500 - 2000 miles depending on who's driving. He drives like grampa, she drives like Dale Jr. Truck burns most when she's driving.

I think there may be a mechanical problem like ring seal, valve seals, pcv or vacuum line. Which one would cause this symptom, or is there another problem?

 

[friendly_jacek]

Yes, if you decelerate a lot, high vacuum in cylinders will suck oil through rings or seals, especially if they are leaky.

This is how Toyota fixed abnormal 5W20 oil consumption in corolla by firmware fix.

 

[toneydoc]

A quart every thousand or so is not a big issue. Will cost you a lot more than a quart of oil to investigate and TRY to repair the source. My solution is to leave it alone, buy 12 quarts of replacement oil, and fill it when necessary. Have a nice day.

 

[hattaresguy]

That's not enough to worry about, when it burns a quart every 100 miles worry.

 

[LeakySeals]

From poisoned catalytic converters to fouled plugs, sensors and exhaust valves that kind of excessive (anything over a quart in 3k) consumption will ultimately cause issues in the long term. An effort should me made to decrease it if possible.

A compression test will tell you more definitively, but the majority of oil consumption problems in older vehicles are piston ring blow by. Worse at higher RPMs where the rings deflect/bend slightly, allowing more oil to enter the combustion chamber.

Valve seals are another area of consumption and give some clues. A puff of blue smoke at cold startup from the tailpipe after sitting overnight. Oil drips by the seal overnight onto the piston head where its combusted, blue smoke for a couple of seconds.

The two problems have different ways of dealing with them. For the rings your hoping for ring coking or being stuck/dirty vs wear or a crack. A piston soak with MMO, Kreen, some are starting to use techron concentrate is a desired action. A thicker oil may help.

For the valve seal issue a High mileage oil would be a good choice. Valve seals are rubber material, so they will respond to the additives in high mileage oil which will condition/swell an old dried out seal making it tighter.

 

[friendly_jacek]

Despite what other people said, this is NOT normal. Use MH oil for entire OCI and report back.

What oil are you using BTW?

 

[ddean]

I have heard that people with 4.6L Fords used aftermarket PCV valves and had a lot of oil consumption that nearly disappeared when the proper Ford OEM PCV valve was used.

 

[hardcore302]

Seeing as how certain manufacturers say that a quart every thousand miles is within spec on a brand new car, I would just start to use some high mileage oil, and let us know what your observations are. I wouldn't lose sleep over it.

 

[jorton]

Huh. Co-worker has to frequently monitor level. This truck is trying to set him up to fail if he feels lazy about checking the level one time.

Originally Posted By: toneydoc
A quart every thousand or so is not a big issue. Will cost you a lot more than a quart of oil to investigate and TRY to repair the source. My solution is to leave it alone, buy 12 quarts of replacement oil, and fill it when necessary. Have a nice day.

So that's bull [censored]. Only experienced F150 owners or mechanics need apply.

 

[uart]

Originally Posted By: jorton
98 f150 4.6 V8 He drives like grampa, she drives like Dale Jr. Truck burns most when she's driving.


Yes, high RPM and lots of slamming on/off accelerator can definitely result in more oil loss though valve seals.

There is also another possibility (or more likely a combination of both). The "grampa" driver may not be getting the oil up to temperature and fuel dilution may be building up, masking any loss of oil. Then Dr Jekyll gets in an gives it a good work out, oil comes up to temperature, fuel dilution is vaporized out, and suddenly it appears like the oil has been quite rapidly lost.

 

[TFB1]

Probably needs valve stem seals, though the fail problem was supposed to be fixed in '96...

After replacing the ones in a '92 Grand Marquis 4.6L and then have them fail in our '93 I just ran it, put a quart in it every 800-1K mi for 65K or so, no big deal... Couple times it had no oil on the stick when I checked it, two quarts would bring it up between add & full... That car still runs every day, though now has had the stem seals replaced... Sold it to a friend, his son repl them when he was between real jobs...

Stem seals in the Ford 4.6L are a major PITA to replace, I did the '92 myself, but will cost probably a$500-$800 at a shop/dealer... Can buy a lot of oil for that...

 

[mechtech2]

Rings/bores getting loose.
But even if perfect, aggressive higher RPMs will use more oil.

High intake vacuum when driving moderately eliminates valve guides from being the culprit.