EyeLuvCorvettes

sooo it's been a while since I have started the car up, been neglected for a bit now. But with it being summer, I went out today to start working on her and get her started up again. I was doing my checks on everything and found that there was a gasoline smell on the oil dipstick . The substance on the dipstick appeared to be far too watery and light in color so I figured i'd just stop where I was at before I blew my motor up.

What could cause this? It's a stock 350 engine (besides sidepipes). I've read about this happening to Japanese cars and causing hydro lock so any help so that I can fix this would be appreciated

Paul L

My guess given recent experience is a ruptured fuel pump diaphragm. Look for gas leaking under the pump.

What backs off from the carb should not get into the oil but just leave you with a dry bowl. But gravity flow from the fuel tank through a bad pump can flood the crankcase. Don't turn the ignition key.

forman

make sure your carbs not leaking or the float may be stuck open ,,, dont run your car ,,change your oil.. how long was the car sitting for

EyeLuvCorvettes

Unfortunately the car had been sitting for about a year.

I'll take a look at the carb and the fuel pump, thanks for the tips

7T1vette

I'm not sure how a leaking carb can get fuel down into the oil pan. Certainly, a ruptured (or leaky) fuel pump diaphragm can do that. Don't start the car unless you have already called the local F.D.

EyeLuvCorvettes

So I can't quite see a leak from the fuel pump. I mentioned this to a buddy of mine and he thinks it may be fried piston rings. Sounds delicious if you ask me! Could that be the culprit?

Paul L

I do not know what seized piston rings have to do with gasoline in the crankcase after a car has sat for a year.

85camarocrazee

Even running a carb that is to large for your carb can cause the same issue. Ask me how I know and what i spent to rebuild the botttom end. Its called fuel wash is actually very common. The fuel washes the oil off of your bearings in the motor causing them to fail. A poor needle/seat can allow residual fuel pressure to bleed off so to speak through the carb into the motor and then sneaking past the rings into your oil pan. Thats how it happens. That would also be my first guess. Rebuild the carb and make sure everything is in spec. Then drain the oil and run it only a couple hundred miles and change it again. Then youre good to go. If the fuel pump was toast and the carb was in tip top shape I would be hard pressed to think it would have enough pressure to push through the carb unless youre running an aftermarket pump with higher pressures. (which could be the problem anyway if thats your set up and youre not running a fuel pressure regulator.....

85camarocrazee

And it usually causes the rings to wear out prematurely as well.....

7T1vette

Fuel wash is a bad thing. But the question is how does the fuel get into the crankcase from the carb???? A leaky carb would put fuel on top of the intake manifold OR into the intake manifold....where it would be burned as a "rich" fuel mixture. I don't see how a leaky carb could put fuel directly into the crankcase.

P.S. If you get fuel into the crankcase, fuel wash is the least of your worries (even though it can do a lot of damage).

Jud Chapin

I believe another happening that can cause this is very short run times such as backing the car out of the garage and shutting it off. Than later on, pulling it back in. Over a period of time with the choke always on when the engine is running, fuel will wash down the cylinder walls and into the oil. This happened to me.

85camarocrazee

Pretty simple.... the entire mixture isn't being fully burned. An engine with a 12 to 1 afr can have this problem ideal is 14.5 my whole dyno run was an average of 12.7 to1

85camarocrazee

Pretty simple.... the entire mixture isn't being fully burned. An engine with a 12 to 1 afr can have this problem ideal is 14.5 my whole dyno run was an average of 12.7 to1

edit... as I was tearing the motor down for the rebuild I couldn't get over how EVERYTHING in that motor stunk of fuel. Even the rocker arms. The connecting rods are still on the bench. I can walk over pick one up and it still stinks like fuel. The rebuild was a month ago!! The only thing that touched every part of that motor was the oil. For it all to smell like fuel means there was fuel in the oil clearly. To answer the next question..... the motor made 397 hp and 422 tq running just like it was!! The rebuilt motor is running exactly the same everything except for a smaller carb. No dyno yet but it feels much more responsive power is up and the mileage went from 13 to 19. Well the drives it most of the time to and from work lol

If you get fuel in the crankcase fuel wash is exactly what will happen. fuel washing the oil of any internal part of the engine is clearly called fuel wash. Im not trying to be rude and please excuse me if come across to anyone as such. My intention is to be to the point.

7T1vette

I agree that, if the carb leaked enough fuel [with engine OFF] to cover the intake internal surfaces with fuel to the point it actually ran down any open intake valves into the cylinders, that could cause your problem. That would be one heckuva leak!

85camarocrazee

It takes alot less fuel than one could imagine..... Like I said. My afr was rich. No other carb issues than just plain ole too big of a carb. a leaky carb would just do it faster. My motor only had 10k on it too......... ran the same way from break in to failure. Theres more than one reason why Carb manufacturers point to a specific carb based on engine size and set up........... 6 months ago I would have said to run a 750 cfm on that 350sbc. Nope not anymore.

Back on topic though.... id say its worn or dirty internals in the carb of the original poster. UNtil someone tells me hes got a brand new carb or rebuilt by someone with a pile of experience thats my diagnosis. Id even lay $$$ on it. Hell Id bet that spare 750 Holley on my shelf on it LMFAO!!

doctorgene

Choke, who runs a choke, I Vote for the fuel pump diaphragm, A good electric Carter fuel pump will stop that. Have a great day. Gene

85camarocrazee

Also. Fuel goes from the fuel pump to the carb as we all know..... so even if the pump diaphram is toast, how does it get past the carb unless the carb is faulty. Carbs are designed to not let fuel flow unless it's called for and thats done when it senses engine vacuum. Wow back to basics............

7T1vette

The stock fuel pump is mounted to the lower section of the block. If the diaphragm ruptures, the fuel just goes directly into the block area which drains to the sump/oil pan.

Mike Ward

You owe somebody a carb then.

GM built millions of 350 cu in SBCs with a 750FM carb on it.

Carb size alone will not cause an engine to run rich or lean.

85camarocrazee

I clearly overlooked the passage between the pump and the pushrod.... Thank you.

Yes gm did but they def did r/d on the setup to make sure the carb and motor worked together. I in no way implied that a 750 will in no way no how work on a 350. They do everyday and work absolutely awesome. Most people fail to realize that with a smaller carb you can make much cleaner power with better mileage. I am in no way saying that every Tom Dick and Sally should never use a 750. I also in no way implied that carb size alone dictates rich or lean. Carb size as we know based on how many CFM (cubic feet per miute) that carb is CAPABLE of flowing. Has nothing to do with whats in said carb although most carbs of the same cfm tend to usually be close on the settings to one another.

How do I owe someone a carb when his situation hasnt been resolved yet..... Better yet I never flat out said NOW HERES THE DEAL< IF BLAH BLAH BLAH THEN I OFFER UP THIS CARB. That would be flat out stupid from a betting stand point for the simple fact that all he would have to do is tell me that I was wrong and owe him a carb. I run a business for a living so Im not going to run out on a plank and wait for someone to push me lol. People will try hard enough the way it is Anyway........