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Fuel System PSA


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Here's a little tidbit for folks, hopefully others find it useful.


Had the car at a test day this spring, could smell fuel from time to time, but no drips, no visible leaks.  Just could smell it faintly.  Took the bulkhead apart to look and nothing is obviously wrong.  Used compressed air to put a little pressure to the tank, started at about 5psi with the cap off, then put the cap on and blocked the vent.  Could hear the air coming out, but not finding any leaks using soap suds like you would for a bike innertube.  Eventually tracked it do the fill plate.  Remove fill plate and look at the gasket - no issues, but that gasket is as hard as a rock (or my head as some say).


The car is a 1994 Miata.  I am quite certain that gasket is an original part and although is not as old as I am, has lost all its compliance.  New gasket was under $5 and will arrive in a couple of days.  Quite an easy fix while the car is in the shop, but would have been a race ending event had I not found it.  Would have been a very bad day had it caused a fire.


Thought I would share this since my guess is that most Champcars are on average more than 20 years old.  There was nothing suspect about my car and the leak was pretty subtle, nothing visible.


Let's not burn up anyone.

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7 hours ago, MMiskoe said:

Yes, the oval shaped cover about 6" x 8".  It could be sealed up with RTV, but not in a 5 minute stop.

No!!!! Never use RTV in a fuel system, I did that thinking that it would dry around the fuel sending unit o-ring, ( just to make sure it wouldn't leak) it was a month later before I added gas to the tank, the RTV oozes out once gas contacts it and fell into the tank an was sucked up on the screen in the fuel pump, one good test session followed by 3 bad ones! Then home and saw the RTV in the fuel pump inlet!

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Troy turned me on to Seals-All.  Works on fuel systems and fixed this exact issue on our car before a race a few years back (ours was a tweaked FP flange keeping the o-ring from sealing.  Always keep a tube on hand now.

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