As some of you know I recenty bought a 95 F-250 5.8/C-6.
It has 150K. Original engine/trans.

I drove the truck around town a couple weeks to work out some check engine light issues. I ended up replacing TPS,IAC valve, and CTS. I have gotten rid of all the codes and passed an emission test.
During the couple weeks I put about 500 miles on the truck. The oil level was full when I bought it and did not use any. I do not know what kind of oil was in the truck nor do I know how long it was in there. It looked clean and was not thin or anything unusual.

I had to make a trip to Fargo, ND from Austin so I ran by the Jiffy Lube for an oil change and transmission flush. They put 5w-30 Quaker State oil in it.
I drove it a couple days and checked it. It was full.

I started on my trip and fueled up in Ft Worth (200 miles) and found the oil 2qts low. I put 2qts of 10w-30 QS in it.
The next fuel stop (200 mi) I put another 2qts in it.
The next stop It was only 1 qt low so I put a quart of Lucas in it.
The next stop I added 2 more qts and my milage dropped from 13 to 10
It finaly went back to 12mpg but is loosing 1-2qts every 200 miles.

I do not see any smoke.
I do not see any leaks or oil under the truck.
I do not see any oil slung under the truck like a rear main seal would do.
Both filters in airbox are as clean as they were 1000 miles ago


I know the C-6 does not have overdrive but the engine does not seem to be running too fast. I have been driving 60-70MPH and I am not towing anything.
The truck runs perfect in every way and vacuum gauge shows steady 24hg at idle and steady 24hg at about 2000 RPM.
I am leaving tomorrow night headed home and wonder if I should change the oil and use 10w-40? or keep adding 10w-30?

Any things I have overlooked?
Any help would be appreciated.
Best,
Justin

 

Well in general QS sucks. I'd use castrol or valve. But I can't see where oil would disappear.

 

bump to the top.

 

Heh.

Mine is wierd also.

However, Mine will just randomly be down a qt, at random. Most of the time it holds it all just fine.

5-30 is way to thin. I use 10-40.

Lucas is nice, but if your looseing oil, then you are definatly wasteing money putting that in there.

I"ve been running seafoam in mine now. And i am haveing less oil loss. I'm not sure if it got in the seals and made them better. Unsure on the seafoam power (man that stuff is awesome)


I think what happens, with your's and mine. Is the old rings when they are goign for a while is letting oil by into the cylinder. And then burning off. HOwever, I do not understand how your looseing 2 qt's in 200 miles.
When i'm randomly just looseing a qt driveing around, and none during long trips.

This is just like the mystery of why the truck takes 6 qt's of oil, but you only drain 5 qt's out.

 

My truck does the same thing, and I was told that the rings are bad, the only sign
that I have is the oily residue on my rear tire and wheel (my exhaust exits out in
front of the rear wheel). Try this for a visual, get up to highway speed 60 - 70 mph
and let off the gas and if possible you or someone with you watch the exhaust exit
for black exhuast soot, theres your oil. Atleast for me that is the only sign I've got,
bad rings.

 

mine to...it gets to a certain level and doesnt drop more.. just below the recomended level on the dipstick.. but as we inspected it its my backseal .. its leaking from there

 

Thanks for the tips gang.
I will change to 10w-40 and report upon my arrival home.
Best,
Justin

 

The sea foam in the oil supposadly will free the rings up if they are sticking.

Perhaps the heavier oil will help out.

I put a whole can of sea foam in when i do my oil. Oil lasts a lot longer also.
This woudln't be so fun for you if you keep looseing oil. But if its just stuck rings. then the sea foam should get em unstuck.

 

where do you put the seafoam ? in the oil ?

 

Yea, I run seafoam right in my crankcase oil.

It's kinda handy to completly clean out all the qt bottles too. I throw some in and shake it up as i go. So the seafoam mixes in with the oil. instead of being a liquid to mix in with the pump.

I have old oil out in the garage I took out last oil change, still is somewhat honey colored. Not black and gritty. had 4500 miles on it. It was just regular valvoline 10w40, and i run motorcraft filters only.

 

For clarification: so there are NO leaks?

 

No leaks.
It used about 6-8 qts of oil on the way home. I used 10-30 Motorcraft brand oil and filter.
Seems only to use oil when I drive over 60 mph.
Am I turning too many rpms maybe? C-6=no O/D
Thanks,
Justin

 

When I fist got my truck 2 months ago...I noticed the same problem (high oil usage at high speeds). Like yourself, no leaks, no burning oil, everything seemed fine. Since I decided to take it easier on the gas pedal to save some $ at the pumps and keep it at 55, I have not had to add any oil in about 6 weeks. I also have a C6 with 4.10 gears. I'm no mechanic, but the correlation between lower rpms and no oil consumption seems evident to me (regardless of what causes this...rings etc...). Could be that the OD-less C6 revs higher then other trannies. Also, I'm not sure about this, but I think the higher the gear ratio, the higher the rpms to maintain a specific speed. (please correct me if I'm wrong here).

That being said, if you have time, take it easier on the gas pedal!!

Cheers
Itch

 

Check your plugs, you gotta be burning it. Also, check your PCV valve to see if it has vacuum. You may find the fitting where it goes into the manifold plugged with carbon (has happened to both of my Windsors).

 

QS is crappy oil...and I was gonna blame it on that.....worn engine seems to be what the problem is.....as for the mystery of 6 quarts in 5 out.....filter holds one quart......