If the only thing wrong with the engine is the cylinder heads, yes you should replace just them, Getting a rebuilt motor is expensive and not needed unless the motor has been damaged beyond repair.
The cylinder heads are diffrent. Intake from 1998 truck will not bolt up to 1990 heads.
There are two cylinder heads on a V6 3.1L engine.
Typically these terms refer to rebuilt engines. And two different ways of ordering them. The Long block comes with rebuilt heads already on the engine, the Short block comes without the heads on the engine.
There are ( 2 ) cylinder heads on your 4.0 liter over head valve V6 engine
yes
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The easiest answer is when it fails a compression test. Buy a compression tester (farily cheap), and test each cylinder. If one single cylinder is below 120 psi, or if one cylinder reads 15% less pressure than the cylinder with the highest pressure, your engine should be torn down and checked. The problem might only be in the heads, but it's still time for some serious work.
Have the engine heads rebuilt using hardened valve seats.
TBI heads/ Throttle body injection
In the cylinder heads.
headboltstork
The Ford 4.0 liter V6 engine ( both the OHV and SOHC ) ( has 2 engine cylinder heads )