tomdoc

Help with diagnosing why I have fuel in the cylinders and and crankcase of my 68 427 L71. I went to start my motor the other day and the motor would not turn over. Thought I had bad starter so I changed it and still wouldn't crank although I could tell starter was engaging. I then tried to turn the crankshaft using the crankshaft nut with a socket and breaker bar. Still nothing the motor is locked up. I removed the spark plugs and fuel came out on a couple of cylinders. The motor then turned right over and more fuel gushed out the cylinders and finally dried up. I replaced the plugs and the motor started right up. But I noticed oil pressure dropped off right away. Only ran the motor for 20 or so seconds and shut it down. Then I checked dip stick oil level and found gas in the oil. The level was about 3 inches above the full mark on the dip stick.... quite a bit of fuel in the crankcase....... The gas tinned out the oil and I'm sure that's why no oil pressure. How did this happen and is the motor damaged or just a bit dry ??? Now let me mention this. The day before this happened I drove the car about 50 miles or so. Motor ran strong and hard like a L71 should... Not as much as a hiccup from this motor.... At the end of my drive that evening I filled the tank to the very top. Right to the filler neck (with 100 octane leaded fuel). Drove the car home from filling it up about 1 mile and parked it in the garage. The next morning the motor was bound up with fuel. Could fuel have siphoned up into the carb past the needle valve and leaked past the rings filling up the crankcase ?? The tank in the C3's sits very high. Any ideas to this mystery ???

ezobens

The only way you can get fuel into the cylinders is via the intake (carb).
I think you are on the right track that fuel was siphoning from the tank and down the intake.
You are lucky you didn't bend a rod or a valve trying to start the car!
Did you happen to look in the tank after you saw all the fuel?
My guess is that it was no longer full .

Not sure what carb you are running but if it's a Holley, the power valve may be blown or you just have a bad float or needle/seat that isn't closing properly.
As far as engine damage, 3" of fuel in the crankcase is a LOT. Your best bet would be to drop the pan and check a couple bearings to see if you wiped anything out.

ignatz

I had exactly the same thing happen. Filled the tank up to the neck one afternoon and drove home. Went to start the next day and I at first figured the starter had died although it sounded odd. Finally figured that the motor was hydraulically locked. Long story short the cool gas from underground expanded in the tank, overpowered the needle valve and flooded everything. The tank sits pretty high and once the needle valve opens the gas just kept coming I guess. Fortunately I did not start the motor. You may be OK, nothing to lose by draining everything, airing out the cylinders , prime via the distributor and start it up.
Now, I never ever fill to the neck.

Kacyc3

check the floats in the carb one being stuck could cause the carb to not stock fuel from overfilling the bowl and leaking into the engine.

Les

You may have dodged a bullet. I had a similar thing happen in my avatar car, except I was on the highway when it began. It started burbling, clearly due to flooding. I pulled over as it was starting to die. Thankfully it stopped running before it fluid locked- that happened as I was trying to restart it. You can hammer the crank and bearings when that happens, especially when the engine is running, so I dropped the pan and checked the bearings- thankfully they were fine.

In your case, I'd be concerned about the bearings since they got washed with gas. If you don't want to drop the pan, as "ezobens" suggested, you could prime it and fire it up. Then let it idle and watch oil pressure to see if it looks normal when cold and fully warmed up. If all seems normal it may be just fine. I hope that's the case. I'd still keep a close eye on oil pressure as you drive it more. Good luck.

Gale Banks 80'

I'd go a head and fill the tank all the way up again and start looking down the throtle bores and see where that fuel is coming from. I'd be a little concerned about an exsposion in the Crank case if it still has a lot of vapor in there. You have probably seen the pictures of a top fuel car blowing the blower off. You can probably get most all of it out the drain plug. If it still smells like gas pump some Air into the empty pan threw the drain with the valve covers off. Then like said above I'd remove the distributor and prime the Engine. With the valve covers off look to see what shows up at the Rocker Arms Oil or Gas. If Gas come out first You will probably have to start the whole process again.

tomdoc

Thanks guys, I'm going to assume Ignats and I had the same problem of overfilling the tank and fuel expanding past the pump and overpowering the needle valve leaking past pistons, rings and filling the crankcase.

I will drain oil, new fillter remove plugs and prime thru distributer and hope there is no motor damage...... And obviously not fill the tank to the top anylonger !!

JimLentz

Also see if you can remove any remaining gas vapor through the PCV valve. Hook to a vacuum cleaner or some other vacuum source.

tomdoc

UPDATE: Just wanted to update everyone, This weekend drained the oil and fuel mix from the oil pan. There was at least 2+ gallons !!! New filter and oil. Removed the distrubutor and primed the oil pump for several minutes. Started her up and she ran just fine. Let the motor idle for several minutes then drove it for a mile or two. Then completely drained the oil pan changed the oil filter again and new oil. Running great..... Thanks for all your input !! Tom.

Les

Hey, that's good news! Glad it worked out well.

Skid*MARK

This is a quite common problem more so with tri power cars.
My friend was not as lucky as you when he did the same thing, went for a short drive and filled the tank full for a trip the next day, parked it in the garage and the next morning it was locked up.
He could smell the gas and figured out what happened, bad thing was he pulled the plugs, had it on jack stands working on it when he hit the starter to spin it over the starter was full of gas from running out the spark plug holes and it went up in flames.
next bad thing is he hit it with a water hose and spread the fire all over garage and car.
finally pushed the car off the stands out into the street to save the house and got it all put out.
He managed to save it all but did about 20 grand worth of fire and water damage to his car, a 69 tripple black NCRS restored 435hp-427 convertible.

WESCH

Hi

First of, thanks for the honest report of this incident, but

starting a motor up that was flooded with fuel inside the cylinders , is kind of stupid, isn't it ?

Furthermore, tripower cars have vented fuel caps , can the fuel still be pushed into the engine if the vented cap works correctly ?

Your reports now make me dizy, will check oil level before each drive if the car was standing for longer time .

Rgds. Günther

joewill

there are supposed to be check valves in the fuel pump, vented gas caps, and needle and seat. all should shut off the flow of fuel with the engine off. doesn't the l71 have just the one fuel line and not a 2nd for a vent? and no vapor canister to relieve pressure?

filling it to the top will not allow any vapor to compress and instead the fuel itself will expand hydraulically as temp increases. ( did it sit in the sun, or park it in a hot garage? ) causing any check valve to release and flow fuel. a 18 gallon tank will expand by about a quart when the temp is raised 20-30 degrees.

in order for it to expand so much that you lose over a gallon and lock your engine means you really have a bad check valve in either your fuel pump or one of your 3 needle and seats. or one of your floats is way out of wack. also, does a vented cap vent both ways from both positive and negative atmospheric pressure? when the check valve fails, the siphoning will occur only when the fuel level is above the needle and seat.

I agree that nothing positive happens when you fill it up to the very top, then park the car.. but you should never lose over a gallon.

larrywalk

Please don't do this with a vacuum cleaner. Gasoline fumes are explosive - many vacuum cleaners use a series motor which has brushes and these make electrical sparks where the brushes contact the commutator.

JimLentz

Excellent point. What would be a good source of vacuum that wouldn't have an ignition risk?

Haggisbash

Why not do it the other way round? Pull the PCV valve, the dipstick and the oil filler cap then blow air through with an air line.

Just a thought - if you have a return line from your carb maybe the fuel made its way into the engine that way?

I had a similar problem when I filled the tank to the top but in my case when the fuel expanded it siphoned out through the return line which is not used on my carb. The return was blocked off under the car with a rubber stopper but this had perished so the fuel dumped all over the garage floor, luckily I was nearby and managed to siphon enough fuel from the tank to stop the flow and then had a very nervous clean up job to do (the garage is under the house).