While replacing the thermostat I found two pieces of hard black plastic. One was wedged in the thermostat keeping it open, and the other was laying in the area underneath the thermostat.

Any idea what these could be from?

Thanks,

Leo

 

Most likely pieces of the intake manifold, get ready to replace that...

 

My thoughts as well lol

 

What is the failure mode of the intake manifold? Will it leave me stranded?

 

Pieces of gasket or inside of hoses can get hard with age and appear similar to plastic as well. If any work was ever done on system it could be debris.


Not usually. Leaks start out slow, losing cooling, either externally or internally, sometimes with misfire, sometimes not. It progresses over time though. There is always the potential for a sudden catastrophic leak, but its not the normal way.

 

You will start to leak coolant at the intake manifold under the thermostat.

Here is a pic from A7X of what his looked like.

 

Underneath the thermostat on my truck is aluminum. Does that mean that this part has been changed out? 2003 F150

 

That crossover piece you can't get off without taking the entire manifold off. The plastic under the crossover is what breaks.
RockAuto is the cheapest I found for the manifold. $156 shipped for the 5.4 L, not sure about the 4.6.

 

Yep, mine did that. I RTV'd the leak for now, maybe in a bit ill replace the manifold but I can't right now.