Burnt Valve?

Just adding my 2 cents for those that are trying to keep track of how many people had this issue.
It happened on my truck 2017 with 60050 miles. Just 50 miles out of warranty and was told it would be 6k 5o fix. Got corporate involved they would give me a 1k discount. This was three years ago, at the time I refused to believe the valves were bad at such low miles. The tech write up also just said that service manual instructed to replace head for the dtc code so felt he didn't do a proper diagnostic job. I performed my own inspection, had injectors cleaned because cyl 5 intake valve had massive carbon build to compared to other valves. When I did the compression test cyl 5 was at 120 compared to 190nfor other cylinder and about 60% leak down. There is definitely a large amount of engines with this issue but from everything I've read it happens at various mileage and different cylinders. Also my truck fried the ecu at the transmission output shaft speed sensor 500 miles before this issue. Most likely not related but figured I add it.

 

Hearing these valve issues, I'm curious what the average rpm these engines were operated at and how long a period. Usually when I've seen valve issues, its always been with an engine running higher rpm than normally should be, and for long periods.

 

2018 Tacoma TRD offroad 4x4
Truck suddenly down on power took it to dealer with no engine light on. Called me back a day later said it was perfectly fine, they test drove it with me and seemed fine now. I have a self fixing truck, couldn't do anything without an engine light on.. so 2 months later did it again, down on power, making weird exhaust noise. Finally an engine light! Burnt exhaust valve, new valves installed still problems, they replaced my full exhaust cats to muffler, still engine light has came on. Boroscope shows messed up piston ring, cylinder wall damage. Well I'm about to trade it in I guess. I don't like any other trucks but what do I do?

 

sounds like from my research don’t buy anything earlier than 2020

 

I often wonder if some of these issues are from running at too low of an RPM for a long period of time. I recall reading posts where owners write about never exceeding 3K RPM's because they want to prolong the life and intend to keep the truck for a long time.

The most recent I recall was someone with an MT that claimed to shift between 2K and 2.5K RPM. While I shift at that RPM too, I also wind it out a bit more and often shift at 3-4K RPM.

I get your point about high RPM for long periods not being good for an engine, but I think the opposite can be true too.

These engines should be able to handle 3-5K RPM without causing valve issues and shortening the life. If not, the redline should be lowered.

 

Agreed. We don't have enough information to say for sure the burned valves are caused by anything specific, but I have often wondered the same, about if it's maybe attributed to lugging the motor too much. I'm a high shifter, I'm more around 4-5K, at least in the first few gears. 3-4K for 4-6.

The dude with over 300K miles said something along the lines of his sees redline or close to it multiple times a day. He has gotten the code for a burnt valve but he also has 300K, so that's much more reasonable.

 

Wonder if any one checked the valve clearance?

 

Don't these motors have hydraulic lifters?

 

What causes a burnt valve? High exhaust gas temperatures.Could be caused by lean mixture. Detonation of mixture. Lugging engine. Too narrow of valve seat or valve face. Poor valve and/or valve seat cooling. Substandard materials used in valve or seat. My advice is to not lug an engine that is tuned by the factory to run lean and hot for emissions/mileage purposes. Run better quality fuel to avoid detonation. That won't mitigate an actual design or material flaw, but may keep you from issues down the road. They upped the allowable ethanol content in gas recently, I wonder if this is having an effect? I feel for the members that have had this happen to them, that is an expensive fix for sure.

 

Do you have evidences to support this claim?

 

Well I believe 4L in essence it is a shim valve engine. The actual bucket is the shim they are different sizes. The point still stands has any one checked the clearance? No matter how it's made a tight clearance will cause issues.

 

Yes, I read it in the Toyota owners manual. And just about every auto manufacturer warns against it. Plus engine manuals often has pictures of disassembled engines showing various issues regarding failures and causes. Engine pictures often show damage to rod and main bearings, and top ring lands in piston. I'm not saying that is what caused members valve issues, just speculating on what may have caused it. Could just be a fluke, as other members pointed out, there are a lot of these engines out there, statistically some are just going to break.I was just putting out some reasons of what can cause a valve to burn, spitballing if you will, so we can perhaps get a better idea of what is causing this specific issue.

 

our tacomas don't run lean.
Here is ECU target AFR table for Port (same for Direct). There are no entries above stoich AFR.


Here is the real time AFR. Spikes to 1.233 (18) when you off of the accelerator (fuel cutoff). Fuel trims constantly being adjusted to maintain AFR. As you can see, there are no constant lean conditions. You will find running below 1.000 80% of the time if not more.