ok so my buddy has 2 burned up valvs on his 1998 Cadillac Deville. What causes this?
The valves don’t seat tightly when they close.
In this case probably sticky hydraulic lifters from dirty oil and extended oil changes.
The valves (especially the exhaust) depend on sitting firmly on the valve seat for cooling.
Once the valve or seat gets a little eroded and hot gases can slip by when closed the problem gets much worse.
This reminds me of my last doctors appointment. I asked him why I was having shoulder pain and his answer “you’ve had too many birthdays”.
Agreed with circuitsmith and I will only add that another reason for burned valves could possibly be engine coolant seeping into the combustion chambers.
More info would help of course. If many of the valves are leaking then the engine may just be getting tired due to high miles.
A lean fuel mixture will quickly burn notches in exhaust valves…A dirty fuel injector or a vacuum leak can cause this…A spark plug inspection can be telling, lean mixtures result in eroded ground electrodes and white, sometimes blistered porcelain insulator…
How was diagnosis performed? Compression check? Or were heads pulled?
WRT to sticky hydraulic lifters, I don’t follow the logic that it can lead to a burned valve.
The normal failure mode for a sticky lifter is that it compresses/bleeds-down a bit when opening the valve, but fails to refill/expand with oil when the pressure is off. The pressure on the lifter to “bleed down” when lifting the valve is far greater than the oil pressure on the lifter trying to refill it.
This means sticky lifters leads to excessive lash, leading to noisy ticking lifters. But no part of that leads to the valve not seating properly.
Has anyone experienced lifters that stick fully expanded?