4WD Rav4 Burns Oil

[dbsoccer]

Don't know if the 4WD Rav4 fits here but I figured I'd try anyway. My question is pretty generic so others may benefit as well.

I recently (10k miles ago) rebuilt the engine in my Rav4 and it burns oil. The rebuild was complete - new pumps, belts, idlers, bearings, rings, valve job, valve seals, etc, etc. I primed the oil pump before I started the motor and my gauge read 75psi or so which is what I'd expect from a new OEM pump. I have no noticeable smoke from the tail pipe or leaks on the floor yet I consume a quart in 1000 miles plus or minus. One thing to note is after extended sitting the engine rattles for a few seconds on start up, like a knocking rod, but then quiets down and sounds fine. The rattle on start up sounds like loose main bearings to me yet when assembled the clearances were fine. I plan to do a compression test, oil pressure test and leak down test.  The oil pressure check is to check the mains. I'm not sure if the leak down test will tell me anything about oil rings function so I will ask. I figured loose mains may increase windage which could lead to increase oil burning. I am hoping someone may have some other areas to check that would lead to fixes easier than pulling the engine back out and replacing main bearings. Thank you in advance.    

Edited January 7, 2017 by dbsoccer
added comments about no leaks.

[Moses Ludel]

Welcome to the forums, dbsoccer...You're welcome here!  So is the RAV4.

I think your idea of a compression test, oil pressure test and, even more useful, a leak down test makes sense, at least to dismiss obvious causes of oil consumption.  From a practical standpoint, make sure the crankcase is ventilating properly and not creating excessive pressure or allowing un-damped suction at the wrong area, which could press or draw oil into the induction system.

Loose mains would not stop knocking after start-up, this noise could be a timing chain tensioner issue, though, which might sound low enough to be a main noise...Crankshaft or excessive bearing clearance that causes bearing oil starvation is more likely an oil bleed-off issue, the result of crankshaft side clearance or other bearing related causes.  

What was the mileage on this engine before tear-down?  You did the work, were the cylinders bored or the crankshaft turned?  What kind of work did you do, was this just a sublet of the heads, new bearings and rings with cylinder glaze busting?  Were oil passages cleaned and the pump screen replaced?  Please clarify.

Piston rings could be installed incorrectly, but I'd be more suspicious of cylinder blowby from piston ring-to-cylinder wall issues.  How were the cylinders prepped?  If honed, how?  How was resulting abrasive removed?  What type of rings were installed?  Pre-gapped?  

Please share more information, I'd be pleased to comment and provide some ideas.

Moses

[dbsoccer]

Hello Moses, Great questions. I'll answer them but first I did complete the oil pressure test yesterday. Idle (~900rpm still a bit cold from start up) the pressure was 32 psi. At ~3000 rpm the pressure approached 70psi. So my fear of loose mains is minimized. I used a new Toyota pump so the numbers are where I'd hoped they'd be.

I plan to go through the PCV system with a fine tooth comb. One line was new and the valve was new (OEM). I don't feel I have a timing belt noise. I did initially as I assumed the tensioner spring would provide the load I needed but I learned new belts relax a bit so I pulled the engine back down and re-did the tension using a new spring and then "going a bit tighter" as advised by some friends in the business. The belt and idlers were new during the rebuild as was the oil and water pumps. 

The motor had 240k miles on it prior to the rebuild. I worked with a quality machine shop in town for my block prep, crankshaft work and cylinder head work. The bores were fine - size-wise and taper so the shop just honed them to "break the glaze". I'm not sure of the exact honing process but I'm confident the didn't use a tool you can buy off the rack at your local NAPA parts store. These guys are known for their quality. Stock pistons and standard rings. I did check ring gaps during assembly. The crank dimensions were fine so I used standard bearings for both the mains and rod. I used pasti-gauge to verify my bearing clearances. The shop polished the bearing surfaces. I took time to make sure the crank's oil passages were clean using brushes, etc. I used the  original pump screen but it was very clean as well. I did wipe down the cylinder walls with ATF as a final cleaning prior to installing the pistions. All of my parts came from Federal Mogul or one of their companies like Sealed Power, etc. I bought a Re-Ring kit from Summit Racing. The kit included the rings, bearings,  gasket set and valve seals all from FM.  

I figure the leakdown will help me eliminate questions about bore prep and ring seating, etc. While I don't think the leak down is intended to test the function of the oil rings one could assume (as risky as that is) if the compression rings are sealing (which is tested via the leak down) the oil rings are probably happy as well. I.E. the honing and sizing, etc provided for proper ring seating. But until I get the test done I'm still just guessing. 

The oil pressure test was good news. What is odd is the tail pipe is not what I'd call black from oil burning. I've seen a good number of vehicles that burn oil and their exhaust pipes are typically coated with oil and/or black soot such that your finger would be a nasty black if you wiped the inside. While this car's pipe has a black coating it isn't what I'd call excessive. And there are no apparent leaks. 

Anyway, I'll keep plugging away.

Thanks for your help and insight. 

Brent

[Moses Ludel]

Brent...The PCV system is a good place to check.  If the machine shop honed the cylinders properly, they would have used a Sunnen CK-10 type machine with the cylinders 90-degree referenced from the crankshaft center line.  Honed to the correct finish (the right degree on crosshatch angles), if the FM rings are moly type and not "chrome", break-in should be no more than 1000-1500 miles.

Regarding rings, the cylinder leakdown test is deadly accurate.  By design, the compression rings, at least one, has an internal ledge that should face upward as instructed in the ring installation notes that came with the rings.  That inside ledge pushes the ring snugly against the cylinder wall as the piston rises and compression increases.  This is a design feature that ensures good ring seal and also oil control, although the oil scrapers at the oil rings are generally considered the primary oil control feature.

Since the leak down test is with the piston at TDC of its compression stroke, this is also the point in the cylinder with the most taper and the highest likelihood of piston ring compression leakage.  I have used a leak down tester since they were popularized (1970s/'80s) after discovering how useless a compression gauge can be when trying to confirm actual cylinder wear or taper.

Ironically, it was a Toyota 18-RC engine that taught me this lesson.  In that test, the cranking compression with a compression gauge was on the low-normal side yet a cylinder leakdown test revealed cylinders that were leaking around 75% with the pistons at TDC!  If I ran a leak down test with the pistons lower in the cylinder and valves closed, the leak percentage diminished dramatically:  This told me there was cylinder taper before I removed the cylinder head.  How does this happen?  When the crankshaft is rotating and the piston is dropping and rising in the cylinder with no firing loads, the piston may be able to capture enough air and press it into the combustion chamber, at least momentarily, to achieve a normal compression reading.  By comparison, the leakdown tester applies continual compressed air pressure (from the shop's air compressor) during a leak down test.

A compression gauge might work okay for an engine under no firing load and just cranking over without spark; however, with increased firing loads within the cylinders, especially when vacuum drops and cylinder pressures rise under load, the rings will leak under both the compression pressure and also on the power stroke.  Cylinder taper exaggerates the amount or percentage of leakage.  That's why a test at TDC, with the valves closed and using a leakdown tester, is so valuable.

Assuming that your engine's valve guides were drilled and silicone/bronze guide liners were installed and finished (not "knurling" the original guides, which leads to premature guide failure), there should be no issue with valve guide oil control unless the guide seals were not installed correctly.  Look over your machine shop bill to confirm the valve guide service method and a charge for either guide liners or new guides.  

Oil consumption at the rate you describe may not be apparent at the tailpipe, as the oil gets processed through the catalytic converter and little if any visible smoke may show at the exhaust pipe.  You could check the tailpipe readings on an engine analyzer to see if there is excessive HC with comparatively normal CO and NOx, which might indicate motor oil burning.  Doubtful it would show up with the engine under no load, though, especially at the slow rate your engine is using oil.

A more traditional test is whether the tailpipe shows blue smoke at startup after the vehicle has been parked, a clear sign of valve guide or guide seal seepage.  If you coast down a 6% grade then open the throttle, if blue smoke belches out the tailpipe, this is likely guide/seal issues.  Blue smoke under hard acceleration is usually piston ring blowby.  These symptoms must be somewhat extreme to be visible with a catalytic converter system, but these easy checks are worth a try.

Let us know what you find.  All sounds fairly right on the build, let's trust there is a simpler reason for the oil consumption as long as the valve guides are sealing, piston grooves were clean, and the piston rings were installed and oriented correctly (oil scrapers staggered properly, too) during your engine assembly.

Look for the minor issues, rule out the major ones...

Moses  

[dbsoccer]

Hello Moses, 

I completed my compression checks and leakdown. I used a Snap On compression tester and two different leak down testers. I built a leakdown  and used an OTC to validate the readings of my homemade set-up. It turns out the readings of both leakdown tester matched well within the accuracy of the gauges used (+/-3-2-3, typically) so I'm happy with my home made tool!

Compression was 175psi+ on all four cylinders. They were all within a couple of pounds of each other. The leakdown readings ranged from 4% to 7%. To me this means the motor is tight. Just driving it I can tell it has some pretty good pep for a 2L stock engine. The Rav4 is a heavy car for its size and it accelerates pretty nicely. 

With regard to the PVC, I crimped the line between the PVC valve and where it ties into the intake manifold. As expected the rpm dropped 50 or so. My understanding to date, is this simple test will verify a work PVC system. I have not concluded that yet, however. There may be other things to check in this system.

Any ideas? 

Thanks. 

Brent

 

[Moses Ludel]

dbsoccer...Compression is outstanding...The 4%-7% is better than good.  During the break-in point, I would expect 8%-10% at least, and that would be a very good seal even after break-in.  4% to 7% is exceptional.  You said that you gapped the rings, so narrow gaps should not be the reason for the low percentage of leakage, we'll just call this an unusually good cylinder seal.  You can rule out any kind of compression loss.

Keep after the PCV and emission system, this would be a simpler remedy if there is an issue here.  Look over the EVAP system closely as well...Beyond that, an engine that has this kind of cylinder seal and still uses oil would likely have a valve guide or guide seal issue, or possibly a deflector or baffle missing within the valve cover area.  This last prospect would be related to the valve spring and guide seal areas getting flooded with an undo amount of oil.  A defective or unbaffled PCV valve can suck oil, too.

Guide seals can be damaged, installed improperly, or actually be the wrong type of seal.  If the shop installed new silicone-bronze guide liners or new guides, they must be match fitted (for proper clearance) to the valve stems.  Otherwise, oil will leak down the guides at a higher rate than normal.

Short of looking over the machinist's shoulder while he did the guide, seal and valve stem work, it's impossible to say whether that work has been done right or not. Also, did they reuse the original valves or replace all of them, or at least replace the exhaust valves?  We're assuming that the valve stems are not worn, tapering or galled.

I avoid condemning shops and their work without having good reason to do so.  When there are no visible leaks, the oil rings are installed correctly and the engine has the kind of cylinder sealing you describe, if it does not stop using more oil than you want in the next several hundred miles, and if this rate of oil consumption is more than you should live with, I would check the stem-to-guide clearance, the guide fit and the guide seal installations.  Before doing any of that, make sure the crankcase is venting properly and all PCV and EVAP functions are normal.

What kind of oil are you using?  What kind of oil did you first run after the rebuild?  What weight/viscosity?  There are concerns involving the oil...

Moses

[dbsoccer]

Thanks Moses, 

Yes this is a mystery. I did learn also the guides where either to spec or they were replaced when I had the head reconditioned. I believe they replaced all the exhaust guides and left the intakes alone because they were to spec. I installed the seals. I recall they snap into place but I can check them without pulling the motor. It's not easy but it is much easier than a motor pull. I still feel the issue has something to do with the crankcase/PCV/EVP/etc. I have a new PCV valve to install but not sure the current one is defective. Both are OEM. But one thing that bothers me is when I go to check the oil the dip stick has 'popped out'. By this I mean, the top of the dip stick has a rubber gromment of sorts that goes into the dipstick tube. It has an interference fit so you need to push it to get it to be fully seated. The rubber holds it as well as seals the crank case at this point. But each time I go to check the oil after it has been driven for any period of time, the stick is no fully seated. Hmmmm? I need to measure but I would assume the bottom of the tube is below the oil level when engine is off. But when it is running I would expect, at least momentarily, the bottom of the tube is uncovered. The oil level drops because oil is pulled up into the motor etc. But....... in either case, the crankcase should be under a slight vacuum and not have a positive pressure. That is if the PCV system is working as intended. With the engine running I measure a vacuum at the engine side of the PCV of roughly 15 inches of Hg (I'm at 5000 feet). The dip stick tube has neither any pressure or vacuum at idle. I need to check at higher RPMs. I would expect to see a vacuum. If there is a vacuum or nothing, the dip stick should stay in place. Not sure what but the stick may becoming unseated for some other valid reason.

My wife just told me the previous owner of the car said it consumed oil as well. Your comment about deflector or baffle missing is interesting. If oil was not returning to the pan quickly enough and preventing the vacuum from the PVC system from reaching the crank case pressure may build up. If the cam clearances were too large it may cause an undo amount of oil to be in the valve cover again, flooding the oil return passages so the PVC system wouldn't work. Again, pressure in the crank case and maybe oil is being pulled into the PVC valve. Just speculating here as this doesn't seem to be a classic case of a oil consumer.

I'll continue with my investigation and keep you in the loop. Thanks again.   

[Moses Ludel]

dbsoccer...Yes, by all means check the the crankcase pressure.  The PCV valve by design is closed at idle or high manifold vacuum.  The manifold vacuum should be enough to seat the PCV valve, and 15 in/hg of actual manifold vacuum would be low.  (I'd like to see 18 in/hg or better of vacuum at the intake manifold below the throttle body.)  As engine manifold vacuum drops (throttle opens), the PCV valve opens and vents the crankcase.  

I would check all of your vacuum circuits and hose routings (crankcase and EVAP) to see whether you have sufficient vacuum at the PCV when needed.  Also, a simple check of crankcase venting would be the removal of the oil fill cap (should be baffled) and a check for vacuum there.  At idle, vacuum might be minimal, but as you open the throttle and the PCV valve unseats, there should be distinct low pressure or vacuum here.  You can test this as simply as a piece of thick paper over the opening.  If you want true crankcase venting measurements, there is a legacy gauge for that, see this exchange:  

Like you, I'm concerned about the dipstick popping up.  This could imply higher than normal crankcase pressure.  If that's not from poor crankcase venting, it would be either 1) pressure from piston ring blow-by and compression gases over-pressurizing the crankcase or 2) crankcase windage.  Windage is from crankshaft assembly churning.  That would only be an issue if a windage tray was removed from the crankcase or oil pan.

Not a rush to judgment about blow-by, you had excellent if not "too good" cylinder leakage readings.  I had concern about ring end gaps, as normal leakage for a rebuilt engine would be 8%-12%, and after break-in 8%-10%.  You were sealing at 4%-7%.  Here is an interesting article at Babcox's Engine Builder, useful for explaining some of the piston and ring issues with modern rebuilds: http://www.enginebuildermag.com/2011/02/how-piston-rings-affect-horsepower/.  

What ring brand and type did you choose?  Piston type?  One concern mentioned is back clearance between rings and the root of the piston grooves.  Read the article and see if anything resonates from your build...

 Moses