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Checking scheduled maintenance in the Owner's Manual (Dad saved everything including the original window sticker) I came across this under Other Maintenance Requirements:
FUEL TANK
Draining accumulated water, sediment or foreign materials in the tank, is stronglyh recommended once a year, to maintain the performance of your authorized Mazda vehicle.
(The last 3 words are in bold and seems to be an edit.)
I don't believe this was done in the first 19 years, and I have not done it in the last 21 years.
It does seem like a good idea. I change the fuel filter often, about every 12,000 miles, so is this really necessary?
Having not done this before, and there is a plug on the bottom I can remove, are there any suggestions on how to proceed?
Should I get the fuel guage near empty first, or is it possible to have it under 1/4 and only partially drain it to use the gas to flush out any crud?
Reusing the gas does not seem like a good idea. Maybe for the lawn mower if filtered.
I'd jack the front of the car up and let it sit for an hour. This is because the drain is on the lower drivers side back on that tank and will force the water/crud to that low point. Then I'd drain a gallon out. No need to get near empty. Getting near empty would be counter-productive because the mix is getting more concentrated crud content and rust.
I've never thought of doing this but it sounds like a good idea. The other thing you can do is run heat in the gas. It will displace the water. Getting any crud/rust out would be more important to me.
I did this last year when troubleshooting poor acceleration and "hitching" at speed on my 84SE. Figuring sediment in the tank may have been clogging the pickup filter sock, it seemed like the quickest and easiest way to drain tank sediment. I think it's a 12mm or 14mm bolt, which seats against the tank in a threaded bung straight into the low point. When you remove the bolt, it has a short threaded section and you'll want an oil drain pan or similar. DON'T DROP THE DRAIN BOLT!
A gallon of gasoline comes out quickly, so be ready to get that bolt back in place and don't cross-thread it in your haste. Finger tight, and then give it enough torque just so that it doesn't leak. Don't overdo the torque.
Airplane fuel tanks have pin-valves on the bottom of he tank to drain water and sediment before EVERY flight as part of the Pre-Flight Checklist. I never found sediment or water, but condensation happens overnight in 100LL AvGas, less so with corn alcohol infused auto gasoline, but the concept is the same. My issue turned out to be a clogged Fuel Injection Filter whereby the inlet screen was impacted with rust dust. New filter bolted in and plumbed, and it felt like the car picked up 50-75hp. No kidding, it was a huge performance improvement and must have been a gradual deterioration in fuel flow over time thus that I didn't notice until it became obvious (*not running well).
I'd jack the front of the car up and let it sit for an hour. This is because the drain is on the lower drivers side back on that tank and will force the water/crud to that low point. Then I'd drain a gallon out. No need to get near empty. Getting near empty would be counter-productive because the mix is getting more concentrated crud content and rust.
I've never thought of doing this but it sounds like a good idea. The other thing you can do is run heat in the gas. It will displace the water. Getting any crud/rust out would be more important to me.
Originally Posted by LongDuck
I did this last year when troubleshooting poor acceleration and "hitching" at speed on my 84SE. Figuring sediment in the tank may have been clogging the pickup filter sock, it seemed like the quickest and easiest way to drain tank sediment. I think it's a 12mm or 14mm bolt, which seats against the tank in a threaded bung straight into the low point. When you remove the bolt, it has a short threaded section and you'll want an oil drain pan or similar. DON'T DROP THE DRAIN BOLT!
A gallon of gasoline comes out quickly, so be ready to get that bolt back in place and don't cross-thread it in your haste. Finger tight, and then give it enough torque just so that it doesn't leak. Don't overdo the torque.
Airplane fuel tanks have pin-valves on the bottom of he tank to drain water and sediment before EVERY flight as part of the Pre-Flight Checklist. I never found sediment or water, but condensation happens overnight in 100LL AvGas, less so with corn alcohol infused auto gasoline, but the concept is the same. My issue turned out to be a clogged Fuel Injection Filter whereby the inlet screen was impacted with rust dust. New filter bolted in and plumbed, and it felt like the car picked up 50-75hp. No kidding, it was a huge performance improvement and must have been a gradual deterioration in fuel flow over time thus that I didn't notice until it became obvious (*not running well).
Thank you. Great advise.
Very doable.
I'll also try some Heat on the next fillup.
Recently when chasing my idle issue, I did test the fuel pump pressure at 3.0 psi, and output just about 1400cc for 1 minute.
