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I have been doing some searches on this site and other sites on intake manifold gaskets on my 1998 f150. What I am specifically interested in is when Ford switched from the 3mm to the 4mm intake manifold gaskets on the 97 - 98 f150 with the 4.2 liter engine to fix the hydro-lock issue. I have found out the general rule is any 4.2 built after 01/15/98 has the updated (4mm) gaskets but depending on where the motor was built the actually date could be earlier than that. I am curious because my motor had a build date of 01/13/98 and was built at the Essex plant. I do not want to have to tear my motor down and switch gaskets if I do not have to. Does any on this site have any info when the Essex plant started using the 4mm gaskets? Thanks in advance