Freedommachine:
Thank you for the education! I spent the evening reading threads in the F150 forum that BoozDaily linked to. One of the threads was 4.2L engine mileage to date. One of the posters implied that the later 4.2s (about 2005+) were quite durable/dependable.
No problem, I am happy to help.
Of course I can only speak from my personal experience and subsequent opinions formed on the matter.
Is the problem you are showing possibly related to early 4.2s?
I am fairly confident that I understand the problems causing this issue. I have yet to find any information describing the design revisions that may have been implemented to solve it.
Short answer: I don't know and until I see 'the fix' I do not trust it.
Your opinion - is the gasket coolant leakage and resultant erosion primarily a time or mileage issue? IOW, expect to have this issue every decade or every 150K miles (I'm just making up numbers, no idea as to what they might be).
The kicker here is erosion, corrosion or a combination of both. Once it starts, it never stops. The intake gaskets have plastic dowels on each end to locate them on the heads. When you remove one gasket and replace it, the new one ends up in the exact same location as the old one.
If the mating surfaces are pitted from corrosion or otherwise imperfect, they will begin to weep/leak again in fairly short order.
The gaskets also have metal pads around each bolt hole, this limits the total 'crush-ability' of the gasket. No matter how tight they are torqued, it will always have the same amount of gasket 'squish'.
The best solution I see would be to prevent the coolant from becoming corrosive to the aluminum. Maybe it's a PH balance issue or something like that? Next, a more robust gasket is in order.
I don't think time or mileage would be something that could be pinpointed as a constant although they both play a large role. It would come down to how attentive the previous owner(s) was.
If you are looking a 4.2l truck and the owner stated; "intake gaskets replaced 5k miles ago" it means very little and I would be suspicious tbh. Did he replace the gaskets preemptively? OR did he wait until it was drinking 1/2 gallon of coolant every 1k miles?
The later most likely. This would mean that the head and intake surfaces would look like pic #2 and unless they are resurfaced, the problem will gradually continue to get worse until a new gasket won't do anything more than slow the leak.
If the coolant system was flushed at regular service intervals since the truck was new, I assume this would help. Maybe the gaskets would last 130k before preemptively replacing them?
If the coolant system was never flushed and an inattentive owner just jumped in and drove it? You would get what is shown in #2 and #3 photos above.
Unless someone has extensive service records from a ford dealer, documenting a long life of regular service, I would be hesitant to pay anything close to market value for a 4.2 truck with more than 90k miles on it.
Like you said, maybe they implemented a design change to solve the problem. I haven't seen one so I will stick with "stay away" lol.
