Gasoline Got Into My Engine Oil

[ClareQuilty]

Another mishap befell the ancient Toyota Corolla Ke-70 a few days ago - it died after a short 8 kilometer run (but just after two weeks of long 4-6 hour trips), and wouldn't start. It also reeked of gas. I had it towed in, and the mechanic said that it had gasoline in the motor oil, and that he guessed it might be ruined.

Then a few days later, after he tore into it, he said it was fine. He cleaned the carburetor, cleaned out the oil/gas mix, and changed the oil.. he didn't mention or charge for any specific gaskets or other replacement parts.

The car runs great - a little better than it did before the mishap. Also no signs of loss of compression or damage to the rings/cylinder walls, etc. (no smoke from the tailpipe, either at startup or any time).

So, what I'm wondering is this - how on earth could gasoline get into the engine oil? I would've thought it would require a bad gasket or 'head' or something like that.

Edited December 25, 2012 by ClareQuilty

[kartman]

Sticking float needle you say it runs better engine was probably flooding or you parked it on a hill nose down.

[dutchrdam]

The only way how petrol can come in the engine oil is if there is a crack in the cilinder, cilinder head or in the piston.

[TommoPhysicist]

Can your mechanic speak English?

[Semper]

Who filled the car with petrol the last time? The cap on the valve cover is for oil only.

[transam]

Hmmm, some carbs, if the float doesn't close the needle (float stuck) it will flood the engine and fuel can possibly drain past the rings into the sump, especially on an old engine with worn cylinders or rings.

[funcat]

I've had it happened ones to my CBR...the fuel leaked thru the open needle and flooded the engine...no damage,just changed the oil and cleaned the carburetor....

[mogandave]

I'm thinking a CBR is a bike, yes? Gas could leak down from the tank through the carb, into the cylinder and down into the case, not so with the gas tank below the engine, unless...

Does it have an electric fuel pump, and did you leave the key on?

[Lickey]

QC, ive just had a poke about on the web to see if you car has an electrical fuel pump or a mechanical one, cant find much so far,

If its electric pump, these stop with the ignition off, a little pressure is still in the fuel line at this time but the needle valve in the carb should cope with that, if not, on re-start the engine will pre-ignite causing pinking because of excess fuel, even so, a hot engine will evapourate the petrol quickly,

A Mechanical pump is run of the camshaft, whether it is overhead cam or on the side of the engine, this has a diaphragm inside that is prone to wear, and a small amout of fuel will leak into the engine, gradually topping up your oil level and the fumes via engine breather will cause the engine to run rough,

Because youve had this problem already i was gonna suggest opening the oil filler and sniff it for petrol, all will suggest is keep a very close eye on the dipstick oil level, if it rises, mechanical fuel pump problems,,

[transam]

QC, ive just had a poke about on the web to see if you car has an electrical fuel pump or a mechanical one, cant find much so far,

If its electric pump, these stop with the ignition off, a little pressure is still in the fuel line at this time but the needle valve in the carb should cope with that, if not, on re-start the engine will pre-ignite causing pinking because of excess fuel, even so, a hot engine will evapourate the petrol quickly,

A Mechanical pump is run of the camshaft, whether it is overhead cam or on the side of the engine, this has a diaphragm inside that is prone to wear, and a small amout of fuel will leak into the engine, gradually topping up your oil level and the fumes via engine breather will cause the engine to run rough,

Because youve had this problem already i was gonna suggest opening the oil filler and sniff it for petrol, all will suggest is keep a very close eye on the dipstick oil level, if it rises, mechanical fuel pump problems,,

Yep, Lickey is right , l forgot about the mechanical pump operation . This type of pump (if you have one) is usually bolted to the engine with an arm that locates a lobe on the camshaft, this arm pushes against a sprung diaphragm which creates a pump. One side of the diaphragm is the engine the other side fuel. If the diaphragm splits any available fuel is dumped into the sump and noooooo fuel pressure to feed the carb. I had this happen many moons back on a V6 Ford. Simple pump replacement does it. Noooo gaskets except for the pump which is usually supplied with the replacement.

[ClareQuilty]

Thank guys, especially Lickey and Transam - the car had a mechanical fuel pump in its original form, but it is now on at least its second 'electric pump'. It is apparently normal in Thailand to replace the original mechanical pump with an electric pump - perhaps the mechanical one is hard to source. I consider this too bad as I don't trust electric fuel pumps much.

Anyway, the car has run a few hour long trips now since the repair and seems fine, so maybe nothing to worry about. My mechanic does speak English but not very well.