only uses oil in town

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My f250 uses a noticeable amount of oil in town driving. It uses about a qt of 15w40 in 700 miles. But i can drive 700 miles on the hwy @ 3000 rpm and the oil level dont change.

Odd to me.
 
Originally Posted By: Ramblejam
Vacuum & valve seals.

+1
Had this same issue with a first gen DSM once.
 
Originally Posted By: artificialist
How can a diesel engine draw vacuum? There has to be another reason.


Thanks for the response -- for some reason, I thought Chris had a 460 Ford. That's what I get for not reading thoroughly. My apologies.

Originally Posted By: Chris142
Ida guessed the thick oil in town would burn less than hot thin oil and 3000 rpm.


Have you checked the CDR valve?
 
Try switching to 10w-30, my guess is you have a faulty thermostat and in town you are not getting up to operating temp, thus the oil consumption.
 
Rings/cylinders are hydrodynamically lubricated, which means they wobble during their cycle. Wobbling increases with decreasing RPM and/or increasing engine load. When wobbling increases, it will decrease the minimum oil-film thickness, which will increase the pressure rise within the oil film. This higher pressure rise will result in increased oil consumption, as the wobbling motion will pump more oil by the rings.

You're keeping your engine at a high RPM in highway driving and I am guessing you're not driving too fast. So, the load on the engine is not high and the RPM is high and the wobbling is minimal. If you decreased the RPM (lugged the engine), wobbling and oil consumption would increase.

In city driving, RPMs are usually lower and the load on the engine could be higher as you accelerate, which could result in increase wobbling and oil consumption.

Switching to a thicker oil increases the minimum oil-film thickness and decreases the wobbling but since 15W-40 is already practically as thick as it gets, there is no further remedy.

(Note: I don't expect the oil consumption by the valve stems to depend on RPM or engine load much, as it's mostly determined by the valve-stem-oil-seal oil metering and/or valve-guide clearance.)
 
Try some 10w-30, since you've replaced the thermostat and eliminated cold engine temps your oil may no be reaching optimal temps during stop and go driving, thus the consumption.
 
Originally Posted By: artificialist
How can a diesel engine draw vacuum? There has to be another reason.


I presume it's the '87 he's talking about. IDI n/a will have vacuum because it's non-turbo.

Those were spec'd for 10w-30 IIRC. Check with Jim Allen; he run's an '86 he rebuilt and has good knowledge of the early IH engines.
 
IDI non-turbo diesels don't have throttle plates, therefore no vacuum. There are pulses from the intake valves opening which is how the CDR valve works. If you have a manual transmission on your old 7.3, and engine brake (as I do) down hills, etc. you could pull oil in past your oil control rings and burn it. Or you could be leaking it somewhere (like my rear main seal or oil cooler o-rings), that's why I always buy HDEO on sale!
 
Chris and I have talked about this at length. He's tried 10W30 IIRC. In my truck, I've never noticed much of a difference in consumption between 10W30 and 15W40 and I've run both in 27 years of owning the same truck. More 10W30 than 15W40.

I said this before but my money is on the valve stem seals. I saw a noticeable decrease in oil consumption in mixed driving when I changed mine years ago. I had to change the head gaskets in the '90s (the notorious external leak) so while it was apart, I replaced the VS seals. Notable decrease in consumption, though it wasn't excessive to start.

City vs highway? Usually, they use more oil on the highway at high rpms (mine always has) but it could go back the VS seals. In town, oil temps aren't as high so oil drainback from the rocker area is slowed and there is more oil there to drain down the stems. In theory, a 10W30 might have helped with this as well but it didn't seem to when you used it before IIRC.

Or am I misremembering? You were having trouble finding 10W30 in Apple Valley, so did you actually try it?

I'll also remind you again about the tricky aspect of the Ford IDI dipstick. You likely have that down pat by now, though.
 
Mine uses the same amount of oil regardles of where the level on the stick is.some ppl say that filling it up to full makes it use more. Not mine. It drank 5w40 like it was free. Ill try 10w 30 next time
 
Mine has always used the oil from between the top mark to about halfway down to ADD much more quickly than from that halfway to ADD. When I first got the truck, it only had 7K miles, I was adding oil like mad to keep it at full (I was also using the spec'ed dual rated 10W30 SG/CF PCMO). I finally read a bulletin or was told about letting it run down to ADD and then add only a quart (two quarts from ADD to FULL for those of you who don't own one of these vintage oil burners). It's been very consistent for me and many others... but not all. You are not the first to say that it doesn't really matter in their situation. Who knows why.

Yeah, try the 10W30 HDEO. It will be an interesting test. I don't notice much difference between them in most respects until it gets cold. Truck starts MUCH better on cold days with 10W30, plugged in or not.

Incidentally, had my first failure to start over this cold snap. Truck was outside in -17F, cold soaked for days, snow up the the tops of the wheels. I needed to move the truck to start plowing out. I plugged it in but it only had about 10 minutes when I tried to start. No go. Almost went a couple of times but it was spinning over really slow (combo of cold batteries and thick oil). Let it stay plugged in for about 2 hours... lit right off. I think I remember the truck being able to start years ago in Colorado at -10 without being plugged in... at least that what I (used to) brag about. Not this time!
 
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Originally Posted By: Chris142
Whoops! $24 a gallon. No way im paying that much


Call up Walmart: (760) 946-2030 - Get a price check on Walmart No.: 004214359

They may not (likely) have in in stock locally, but will ship to your local store. Let us know what you find out.
 
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