Hello everyone! My 83 D150 slant six engine burns a lot of oil. Like a quart in less than a 100 miles. It smokes on start up but stops after 5 minutes of driving. The truck runs great and compression is good. I'm wondering if Dan's soup flush would help or is this much oil consumption too much? I did run a quart of MMO in the oil for a while but changed the oil after maybe 500 or 600 miles. I did fix the leaks as far as I can tell.

If it doesn't work I will rebuild the motor or just rebuild now.

Any advice is appreciated. I'm late 50s and not looking forward to trying to pull the motor.

I'll add I wonder if this much oil usage is possible without a leak. I'm not seeing one but not very good at diagnosing that.

I could just pull the valve cover and check for valve stem wear. I would remove the spring keepers and maybe put seals on. Seems like the valve stems wouldn't leak that much.

The alternative is to take it to a shop and get a fix it quote.

1 qt every 100 miles sounds like a tremendous amount without a leak. Is there no oil under the truck in your driveway/garage after you drive it? It sounds like stuck or broken rings, which might loosen up with a flush using Dan's soup. Valve seals (and maybe stems if badly worn) would be another key thing to try, as you say.

How long have you driven the truck, and how long are your typical trips?

Lou

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What is your compression? A leak down test will tell you more for sure.

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12.70 @ 104.6

A few spots of oil underneath after driving. Mostly the powersteering and transmission oil at the radiator. The transmission cooler lines have hose for 4 or 5 inches to the radiator. I should replace the hoses and double clamp both ends. Power steering seeps a bit.

Compression was 125 to 135 on a cold engine.

Have only had the truck a couple of months. Have limited trips to work and back and around town. I live 3 miles from town so it is not a short trip around town. Work and back is about 50 miles. Drove over to Stillwater from north of Tulsa once. Put oil in to drive back home. About 75 miles one way.

Cooling down here so I'm about ready to tear into this motor. Any more input?

I have a similar issue on my '62 valiant wagon.

Burns a lot of oil ~1 qt / 100 miles.

Time for a full rebuild as the rings and bores are not happy together.. other than that is runs fine.

Greg

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Most of that's going away in leaks—you can't burn anywhere near that much oil without giant clouds of smoke all the time, even with a catalytic converter or two.
The converter(s), if still present, will "eat" a lot of burnt oil, but they won't be happy about it for long. How much smoke are we talking about here?
Probably not, but probably won't hurt to try.

Some leaks, even some major ones, are good at hiding; they don't show up until the engine's running at speed and they don't leave a drip trace. Clean the engine thoroughly, put in some UV-fluorescent leak detection dye, drive 50 miles, then get under the hood/under the truck with a UV flashlight and see where the bright spots are.

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Thanks for the response.

No cats left. Quite a bit of soot in the tail pipe and exhaust.

Was worse blowing smoke when I bought it. Ran MMO in the oil and changed it twice. Smokes a lot less now but still a cloud after coasting down the hill a mile or so from the house. Very little smoke after 5 minutes of highway driving.

I wondered if that was too much to burn. Didn't think of the UV die and light. Thanks!

ETA ordered the dye and light.

Dye showed the front of oil pan was leaking. Blowing along the passenger side of the motor. There is a bunch of extra silicon at the gasket. Checked the bolts and 3 were loose. Tightened them and it seems to have stopped.

Some back story, found earlier the valve cover was very loose. Some bolts were a couple of turns loose. Tightened and torqued them down and stopped the oil puddles.

Posting an update. Pulled the spark plugs to squirt in some berryman b12 and soak the rings. Before the plugs were black from oil. Today they are whightish grey.
Don't think it is burning near as much oil as before.

Replaced the valve cover gasket, sender, and oil pump cover o ring. Still using or leaking oil. If it is leaking I don't know where. May replace front cover, seal and pan gasket.

Would be easier to get to with the motor out though. Where else would it leak?

Had the girlfriend rev the motor and laid underneath for a while. Don't see anything leaking.

Picture of spark plugs. They were black before. Have new plugs, cap, and rotor to put in.

Picture

With compression in the 125 to 135 range, I doubt if the rings/bores are totally shot.
Typically smoke at start up is due to oil getting by the valve stem seals.
An 83 slant probably had umbrella seals, those are not great when new. They deteriorate over time.
It is possible to change valve seals with out pulling the head, put rope in the bore through the sparkplug hole,,,,
But simply pulling the head is not a bad job either, then you could renew the seats maybe trim the head to raise compression.
Just kind of depends on how deep you want to get into it.
Back to the compression, 125 to 135 if that is accurate, says the rings are not stuck.

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And looking at the pictures of your sparkplugs,
Those plug’s don’t show excess oil burning.
If you are still using a quart every 100 miles it is leaking out.
Did you do the UV test previously recommended?

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

I did the UV test, showed leaking at the front of the oil pan. Found the loose bolts and tightened them to the recommended torque.

Doesn't smoke at start up like valve seals. Smokes under acceleration.

I'm guessing the oil only leaks when braking to a stop or cornering.

Would the head gasket leak oil? Seems like there is a little oil there at times not coming from the valve cover.

I should redo the UV dye.