need to do a top end on the 4.0, compression way, way down. Have a local machine shop with good rep but with the history of these heads, price and all thought it might be better to go with and aftermarket heavier casting. Looks like the ones to get are Mahle, but cant find if they are still in production. Would anybody know where these can be had or what heads are the members having good results with. Just don't want to drop $500 in my heads if there so prone to cracking.
Motor has 135 K most cylinders under 100 with one at 15, oil wetting brought these up slightly but not much, Leak down, mixed results especially with a 15 Lb cylinder. Have core motor im pulling down now but all in all new castings likely best bet.
Also , bought truck uses at 114K don't know history but it still runs and drives OK without overheating, just down on power and fuel economy. Thanks

 

What year is the engine/Ranger?

All the 4.0l(and 2.9l) heads had thin casting between valve seats, it is the design and valve placement, doesn't matter who makes them.

Trick is, don't ever let engine over heat, simple as that

This isn't a chicken and egg thing, never ran into a 4.0l head that just cracked for no reason, if you dig enough and the person comes clean you will learn it WAS over heated just prior to cracked head showing up.
The crack starts very small and might not effect engine performance for weeks or months, which is why some think it was not related to the over heating that occurred in the past

So have your heads tested and if they are OK use them, save some money

I am close to 400k with original valves and rings, still getting 155-165psi from the cylinders

I would suspect compression gauge, but the 15psi is puzzling
Engine won't cold start with 100psi, which is why I would check that gauge
But exhaust valves could be burnt in all 6

 

Guage is very old, not sure how to check it, guess I could match it against my compressor regulator. Was looking at King Cylinder head just under $300 each, kind of steep. But I bet a local machine shop will be near that for a good valve job. Kings are brand new but don't know who casts them, maybe chinese? Anybody know?
Would like a little more feed back on the stockers, 400 K sounds great on stocks but probably not common. Hey , I'm all for saving a few bucks, just don't want to have to do this again anytime soon.

 

Ranger is a 95, 4x4 automatic, 3.73 8.8 rear.
at this time starts fine, runs in the normal temp range. loosing coolant but no smell at heater vents, no smell at tail pipe, does smell from under hood some maybe intake gasket or slow leak somewhere in a hose or WP.

 

4x4's usually had Limited slip rear end as well

Look at door tag under AXLE, if you see a Letter and number it is limited slip, Ford called theirs Trac Lok, GM calls their positraction

Info here: Ford 7.5 & 8.8 Inch Axle Tag & Door Codes

Water pump probably, they last longer than Chevys but still go out

I had a pin hole leak in upper rad hose, only leaked when system had pressure, so warmed up, squirted coolant on water pump area so thats where I thought leak was.
Changed pump but still had the leak??? WTF
Found it when I was feeling around after engine was warmed up but just shut off, stream hit the back of my hand, but was invisible otherwise.

Also had cracked in overflow hose, it runs across the top of rad, it only leaked when system had pressure and coolant evaporated instantly, found that by accident when working on something else.

These didn't happen to the same vehicle, just saying leaks can be in odd places.