D4 7U Gaskets

Personally I don't like doubling up gaskets, if you can't find a thicker one then I would recommend finding some quality gasket material of the right thickness and making your own, I've done it myself on those several times. I've also found that it's not uncommon to have the top cover of the fuel filter housing warped a bit at the gasket surface, which can cause a leak like the one you're describing. Since it's just an aluminum cover it can easily warp a bit if the nuts are over tightened, which has usually happened several times during the past few decades of these machines' lifetimes. I usually do a flatness check on those covers every time I have one off for the first time. What I do is use a flat, machined surface like the top of my tablesaw and lay out a square sheet of fine sandpaper on it. You can then lay the gasket side of the aluminum cover down on the sandpaper and swirl it around keeping even down pressure on it. It won't take long to see if it's warped, you'll start seeing very clean metal around the bolt hole bores if it is. I just keep going till it looks uniform all across the gasket area and give it a good cleaning when I'm done. Plus a VERY thin layer of sealer on the gaskets doesn't hurt either.

Most gaskets I've bought from Cat have all been the proper thickness though, I know the last one I bought that goes between the injection pump and filter tower was spot on when compared to the old one.

It also may not have been an OEM gasket. I've seen a few where they appear to be thicker than the new replacement. I do a similar routine as Toby described except I have a flat steel plate that I use for checking/flattening manifolds on by using the same procedure.

I can second or third the sand paper and flat surface recommendation. I also glue the paper to the reference surface with some aerosol photo mounting adhesive. It really helps keep the work piece flatter as the edges of the paper will not be trying to lift, and it is easier when using wet or dry paper with some fluid to keep the swarf flushed out. I like to start with a grit that will knock off the high spots and then change to a finer grit if I want a smoother finish.

Thanks for the replies. Appreciate the help.

How tight was the old gasket?And did you hit it to remove?Just helped son in law change filters in a 7u and the aluminum plate that holds the filters had been cracked and would suck air on a hard pull.Was very hard to see I could of missed it but he had seen a small weeping at idle.Other than hitting it to hard the only way I can think of is a limb slapping it or have a lot of water in the housing and freezing doing it.Good luck finding the cause of your problem.

Just a thought, if the cover was loosened with a hammer, there could be a local swelling in one spot keeping the cover off gasket.