2000 Avalon, cyl #2 burned valve

[The Critic]

2000 Avalon, 280K miles. This is the 1MZ-FE 3.0L V6. Previously burned 1 qt/3k miles. Over the last few months, it started burning 1 qt/3-500 miles and just two weeks ago, cyl 2 developed an active misfire.

I am not doing this repair, but I helped the owner with compression/leakdown tests and am guiding him through the repair.

We performed compression/leakdown tests on the front bank. Cyl 2 showed 85% leakdown and 15 lbs of compression. We traced the loss to air escaping into the exhaust manifold, so we suspected an exhaust valve issue. The other two cylinders on this bank had 175 psi compression and 16% leakdown, which is normal.

The owner checked the valve adjustment and said it was within spec (.0012”). He elected to remove the front head. After removing the head, it appears that one of the exhaust valves had burned.

If the valve adjustment was in spec, why did this exhaust valve burn?

Note: the owner only wants to get another 20-30K out of this car.

 

[mattd]

Running lean. Check the fuel injector on that cylinder. How does the piston top look? Lots of carbon buildup? Is the valve bent at all?

 

[The Critic]

Running lean. Check the fuel injector on that cylinder. How does the piston top look? Lots of carbon buildup? Is the valve bent at all?

Quantity of carbon build-up seems normal for the mileage. Normal light coating. Not sure on the valve- the head is headed to the machine shop today.

If this was a single cylinder injector failure, wouldn't the vehicle have experienced a misfire long before the valve was burned? I don't recall the vehicle being driven very much after the misfire started.

 

[supton]

Not a mechanic but what is the color like for the other cylinders? This burned valve doesn't look like the other 3 (I'd expect one other to look similar) so I wonder if it ran hot for... bad seat? Maybe a bad guide? not sure if it can run hot from being loose.

 

[ragtoplvr]

Sometimes a small piece of carbon breaks loose, and holds the valve up. Since this commonly occurs under high load, the valve burns in a second and the offending piece of carbon disappears.

I have seen a motorcycle quit running during a rain storm from the water entering the engine and breaking loose carbon, holding both exhaust valves open too much to idle.

 

[Blinker]

This failure looks to be caused by the overall condition of the engine itself due to the carbon buildup. Likely the carbon buildup caused the valve to stick slightly or the valve seat wasn’t creating a good seal due to the carbon buildup and caused the valve to get too hot.

 

[mattd]

If it happened that suddenly, the it’s possible a piece of carbon was holding the valve open slightly, and just burnt quickly from being held open.

 

[clinebarger]

That's a lot of carbon in my opinion, But pictures can be deceiving. Toyotas have the hardest valve seats I've ever ran across & don't seem to suffer from seat recession like Hondas do.

 

[Trav]

I would think there may be more wrong with that cylinder than just the burned valve, the rings may have issues that allowed it to use so much oil.
A qt every 300-500 miles is a lot of oil. It would be interesting to see the plug from that hole, is the ceramic intact?

 

[The Critic]

I would think there may be more wrong with that cylinder than just the burned valve, the rings may have issues that allowed it to use so much oil.
A qt every 300-500 miles is a lot of oil. It would be interesting to see the plug from that hole, is the ceramic intact?

Ceramic was intact.
Head is back from the machine shop. They did a valve job on all 3 cylinders and installed two new exhaust valves for #2. And of course, insisted on resurfacing the head. $375.

 

[andyd]

deleted

 

[PandaBear]

Something must have happened when it started burning 1qt / 500 miles and that several months of acting like that is what burnt the valve.

Wonder what leads to that much oil burn, likely leads to burning the valve.

 

[partspro]

your 2000 is in the list of what toyota called an oil sludging problem and they replaced alot of engines. oil sludge would build up under the valve covers and bake on in hard layers. to over an inch thick. i think that oil break down caused heat and the valve burnt.

 

[The Critic]

your 2000 is in the list of what toyota called an oil sludging problem and they replaced alot of engines. oil sludge would build up under the valve covers and bake on in hard layers. to over an inch thick. i think that oil break down caused heat and the valve burnt.

Valvetrain was clean.
Anyway, it has been more than 5k since the repairs and the car still runs.

 

[vw7674]

Something must have happened when it started burning 1qt / 500 miles and that several months of acting like that is what burnt the valve.

Wonder what leads to that much oil burn, likely leads to burning the valve.

bad valve seals is my guess. at 20+years it's paid for at least twice. three times.

 

[The Critic]

bad valve seals is my guess. at 20+years it's paid for at least twice. three times.

Oil consumption was reduced after the repair.