Okay guys, need some knowledgeable folks to double check me.

First off, the truck is a 1983 Pickup 4x4, with a 22r, owned by me for a few years now. The truck came with a whole bunch of service records, which have been illuminating to go through. It got its first replacement engine in 1986, under manufacturer warranty, then again in 2005, a crate motor from ATK. The first motor that ATK shipped broke the connecting rod on the #4 within a few thousand miles. Que R&R under warranty and now we are on motor #3. Fast forward 14 years and I buy the truck.

The current motor has gone approximately 47K since it's install in 2005. When I purchased the truck it was an oily mess, seemingly leaking from every seal possible (would give me pause before recommending an ATK engine, but that's just my 2 cents). Slowly I have cleaned and addressed the leaks, front main seal, valve cover etc. and now am confident that I am no longer losing oil onto the ground.

However, my oil consumption remains high. About a quart every 350-400 miles. Thinking that a engine with only 47K couldn't have bad rings I pulled the head, replaced HG, valve guide seals, cleaned a ton of carbon from valves and top of pistons, measured everything for spec against the FSM (valves and guides) and put it all back together. Truck runs better without all that carbon, but no change in oil consumption.

So here's the real kicker:

Compression test comes back good, at or slightly above FSM spec on a dry test with a warm engine. 174 on the lowest cylinder, 181 on the highest.
Leakdown test comes back with 7% leakage in all four cylinders. Air is escaping past rings and into crankcase only. Leak down was performed post head job, confirming that I got a good seal on my valves and HG.

So, I'm stumped. With those numbers, I can't imagine where I'm burning so much oil. Current working theories are stuck and or broken oil control rings or plugged piston oil return holes (wouldn't affect compression/leak down, right?). Cylinder glazing from poorly adjusted carb, perhaps during the break in period. Or that somehow there is another way that oil is entering the combustion chamber.

I have recently replaced the PCV valve, without any change in oil consumption.

At this point it's looking like the truck is going to get yet another engine (rebuild, this time, I want to do the work). But, before I tear apart a perfectly good motor, have I missed something here? Would hate to be halfway through a rebuild and realize I forgot to address one specific issue that could have solved the problem.

Would love to hear the groups thoughts. I have photos of the head removed (cylinder walls) as well as sparks plugs, head work etc if folks want to see.

Many thanks in advance.

 

Hows engine performance?
sounds like 7 on a leak test is ok but im no expert.
Any leaks?
The oil pump seal can leak without noticing it bc of the fan blowing

 

Oil pumps wear a groove on the shaft over time so if you dont have a new shaft it could be a problem

 

Do you get any blue smoke when you start the engine or when you rev it up?

 

swampedout, interesting thought on the oil pump. I have not checked there. Would that cause oil to leak when the truck is off, like a front main, or only under pressure?

I should have mentioned in my initial post that I do get blue smoke, but only when engine braking. Living in Colorado, mountain driving is the norm and on long steep down grades I get small puffs of blue smoke from the tailpipe. Puffs turn into clouds when back on the throttle for maybe 30 seconds, until the collected oil burns off. During start up or driving on flat ground, there is never any visible smoke.

 

Im not sure. It is the front main i was thinking abt. I have a leak on mine but I think only when driving. But my motor is needing a rebuild soon.

Im confused abt the smoke while driving. If you have low numbers on the leak test, it doesnt make sense that youd be burning oil. To me that indicates rings. Maybe block the exhaust and try another leak test?

 

Maybe a lame thought, but stuck open or malfunctioning PCV Valve?

 

Or valve seals.

 

If you're using a PCV valve from the part store replace it with the proper part from a reputable Toyota dealer. The plastic part store ones cross reference with tens to hundreds of engines, from memory the last one I got from one of them fit something like 180 other engines. The one from Toyota fits one engine over about a six month period.. It makes a difference.

You touched on having glazed cylinder surfaces, which is likely your root issue. Keep in mind the hone is supposed to hold a film of oil and prevent the cylinder and rings from coming into contact and once this fails you get both cylinder and wear on the rings.

 

Valve stem seals. Leaking valve stem seals won't effect the leak down test when the valves are closed, but when decelerating the engine vacuum is at its greatest and it will pull oil into the intake manifold on top of the valve and then into the cylinder when the valve opens. Poof, blue smoke on decel, probably adding to the cylinder glazing as well.

 

OP says they just replaced the valve seals, and I think he said guides also (?)

Keep in mind a leak down test isn't a plain and clear "go, no go" like compression test where you'll immediately see a out of spec number. It's a bit more "bench mark" I used to run the 100 in X now I run the 50 in X.. You need to know what it was doing before and compare to what it does now, and specifically where is that air going is it out the valves (which side intake or exhaust) or into the crank case.

 

Ive heard of ppl blocking off intake and exhaust to see if that changes leak numbers

 

This line of reasoning is exactly what lead me to replace the valve stem seals in the first place. Unfortunately, unless I somehow boogered up a seal when installing, that doesn’t appear to be the issue.

 

Can you elaborate on this a little bit? I obviously have no way of knowing what the leak down looked like before purchasing the vehicle. But from what I read anything under 10% is squarely in the happy motor category. All of the air that was leaking was pushing into the crankcase, coming out the oil filler cap and dipstick tube.

I did not replace valves or valve stems as part of the head job, just seals. All of the valves and stems were measured with a set of digital calipers and were well within FSM tolerance.

I ended up purchasing a different leak down tester and hopefully have time to try another test today.

 

Good idea on the Toyota specific valve. I will call the dealer and see about getting one for that motor.

Any thought on the causes of cylinder glazing at such low milage? Given all of the “deferred maintenance” I have discovered since owning the truck, it makes me question how often the oil was actually changed during those 47k miles.

 

Because I am not an engine builder, rather learning as I go, here are a few shots of the block with head removed. Do that look like glazing to folks? Enough to be letting a quart of oil sneak past, every 400 miles or so?


All carbon’ed up after first pulling the head

Cleaned and ready to go back together

 

Front main was replaced last year, haven’t had any leakage issues since.

 

Youd need to get in closer for us to see the pattern on the cylinder walls.
Also, id throw that fram filter in the trash. Theyve got a bad reputation.

Glad to see you working on it! A lot of ppl like these old trucks but r scared to get their hands dirty

 

Biggest reason youd get glazing is engine break in procedures not followed properly

 

Unfortunately when I had the head off, I didn’t think to take any close up shots of the cylinder walls. Truck has been down for a little bit while I rebuilt the front axle, but now I am driving it again. Did a piston soak with B-12 while it was on jack stands, thinking at least it couldn’t hurt. Switched to 10w-40 and still seeing no change in oil consumption. Still need to get the OEM PVC, though I don’t have high hopes since after installing a breather in place of the existing PVC on a test drive, it still produced the same volume of smoke, under the same circumstances. Looking more and more like a rebuild is in my future ...