Our own mechanical fuel pump "horror" stories....

As I've mentioned before, I have nearly 2 million miles of Corvair driving on mechanical fuel pumps. I believe them to be totally reliable.

Never the less, we do no one a service by ignoring actual issues. Rather, it's better to get them out in the open and try to analyze them. Here are the ones I have experienced firthand.

Once my stepson and I were driving his 1969 up to a Corvair event in northern Washington. He hadn't put many miles on the new engine but everything was running well. We had stopped at a Wendy's to eat lunch. The 69 was parked on a pretty steep space where the engine was on the downhill side.

After eating we came out and started the 69 up. It was running fine but I was sure I smelled gas. Went to the back of the car and gas was POURING out of the back of the fuel pump. We immediately stopped the engine and pondered our options (I had brought a new spare fuel pump with us - I carry a spare tire and fan belt too).

Because I couldn't explain why the pump was suddenly "leaking" I asked my stepson to start the motor up for just a few seconds so I could see exactly where the gas was coming from. SURPRISE! Gas wasn't coming out of the pump any more. I was baffled.

We watched the pump for about 10 minutes. Not a drop of gas. We proceeded (cautiously) the further 100 miles to the show. No leaks. Then drove home (about 300 miles) no leaks. In fact, this was 10 years ago and the car still has the same fuel pump on it. Not a drop since.

What exactly was going on? I have my theories, but maybe you have an idea.

Another leak story involves my Ultravan. Because it usually sat for months at a time when it came time to start up for a new season I'd have the engine lid off to watch for problems. The last time it had been started was about 9 months before. This time on startup there was a massive fuel pump leak.

I shut the van down and went inside to ponder the situation. About 10 minutes later I went out, restarted the Ultravan, and of course, no leak. The "leak" never came back - even 4 years and 5000 plus miles later.

Our last example is interesting because it just happened to me 2 days ago (August 30th). I had my daily driver 64 Greenbrier down for about 3 weeks while I rebuilt the carbs, distributor, and alternator.

When all the work was done I did the initial startup and SURPRISE the fuel pump that had been serving faithfully for over 60,000 miles was leaking. But this time I thought I'd just shut down for a few minutes and then restart.

Of course the "leak" was gone. And it hasn't come back.

In all the cases above I DID NOT tighten the screws on the pump - In these circumstances many people retighten the pump cap screws and lay the "leak" on the need to do that. But note that, at the same time, there was a short waiting period between "leaking" and not leaking. I'm certain it was the waiting period - NOT the screw tightening that fixed the problem.

But why is it happening? (Even if just occasionally)  It appears that modern fuel dries out the rubber diaphragm between extended intervals of operation. Sometimes (but not usually) the diaphragm material will shrink causing a leak at startup. BUT, once the material is re-exposed to the fuel it "swells up" and re seals.

If you have other ideas let me know.

The last example is what I believe to be very typical. Linda and I drove our 67 out to southern Utah for a Corvair event back in 2000. We had already driven 900+ miles without incident but after meeting up with the Bonneville Corvair club we stopped for lunch (At a Wendys again - hmmmmm I wonder...).

As we left we all drove back onto the freeway and the 67 died out. No fuel. Everyone thought it was a failed pump. But I was suspicious. I went back and checked everything over and noticed that the incoming gas line fitting was loose. Upon tightening it up we had fuel pressure again and finished our trip, including a barren 300 mile return across HWY 50 in Northern Nevada (The world's loneliest highway).

Vacuum leaks anywhere in the incoming line can cause the pump to quit drawing fuel. These leaks can be effected by temperature and other factors. Check these things first , before you assume the pump has failed.


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