Timing, not enough exhaust back pressure, wrong air filter, inlet valve burnt or sticky
Assuming this is a 4.3L engine, the upper intake manifold gasket would be between the upper intake manifold and the lower intake manifold.
Yes. If an intake manifold gasket was not installed properly or has somehow become damaged the engine will pull air through the opening.
No, the head gasket is underneath the heads where they mount onto the block. Your intake manifold is bolted to the top of your heads. Some motors have coolant that circulates in the intake manifold ( I don't know what year or make your vehicle is ) so I would check my shop or repair manual. There could be a crack where the coolant flows through your intake manifold or one of the manifold gaskets may need replacing.
Intake manifold gaskets are leaking, intake manifold is warped.
There are a few causes: Damaged or disconnected hoses (or component) from intake manifold. Worn out intake manifold gasket. Improper replacement of a part. Cracked or damaged intake manifold.
it would be on the top of the moter
On an engine bolted to the intake manifold.
Need to know if it is the intake manifold or an exhaust manifold and what is wrong with it.
A bad intake manifold or manifold gasket can cause water to leak into the oil. Some newer cars have plastic manifolds and they will crack from age.
An intake manifold itself typically does not directly cause a car to overheat. However, if there are issues such as leaks in the intake manifold gasket or a malfunction that allows coolant to enter the intake system, it can lead to overheating. Additionally, if the intake manifold is not functioning properly, it can affect engine performance and efficiency, potentially contributing to overheating issues. Regular maintenance and inspection can help prevent these problems.
Under the upper intake manifold. The upper intake manifold would have to be removed to gain access to the bank of injector poppets (the spider).
The year, engine size and if it is the intake manifold or an exhaust manifold gaskets would help.