What is causing my oil pan to fill with a mysterious fluid?

Question

I have a 1967 Ford Mustang with a 289 small block V8. It had been sitting in the garage for a while (years, actually), so I did a fluid refresh, changed the fuel, changed the oil, and changed the coolant. After fixing an air pocket in the fuel line I was able to get it running and driving and everything seemed fine.

The Problem

However, when I got home I checked the oil level and found it was very high. I thought perhaps I'd added way too much oil on accident, so I changed the oil again, drove the car again, and found the oil level had risen again.

Possibilities

As far as I know there can only be two places additional fluid could be coming from. Either coolant is entering the oil, or fuel is entering the oil. The liquid in the oil pan is not milky. I've smelled it, and it smells like motor oil, perhaps tinged with the smell of gasoline. I tried burning some, but it didn't ignite, so if the additional fluid is gasoline there isn't enough to burn well. I have to conclude it's fuel in the oil, but I'm not sure how to confirm this.

More importantly, how could gasoline be getting into the oil? Besides sitting for a long time, the engine was essentially brand new (it was totally rebuilt in 2010), so there can't be any real damage besides whatever stagnation can cause. I've wondered if perhaps the piston rings are stuck closed and fuel is bypassing the rings as it enters the cylinders while it's running, but the amount of rise in the oil level is significant and the engine doesn't act like it's starved for fuel.

The Ultimate Question

Could there be any other fluids that could be contaminating my oil? If it is fuel, how is it getting into the oil? And most importantly, what do I do to prevent it from happening in the future?

Answer 1

Used motor oil should smell like oil, or oil and exhaust. If you can smell gasoline, you have fuel in the oil.

You said the car sat for a long time. If this engine has not been modernized with fuel injection and it has a carb, the fuel in the bowl may have become thick and sticky as it sat, or turned into a solid. This could be preventing the float valve from fully cutting off fuel flow when the bowl is full. Fuel can then overflow into the intake manifold and find its way into the crankcase through the cylinders and rings. It will be in the liquid state and not atomized, so it's hard to burn and will seek a low point with the motor oil.

Suggest you open the carb and see if the fuel bowl is over-full. If so, you may have to clean the carb to stop the leaking.

EDIT:

And by the way, you can identify fuel in the oil by placing a drop of oil on filter paper (like a coffee filter) or even a paper towel. Observe the drop for a few minutes and see how it spreads. If it spreads into a uniform circle, it's pure oil. If it spreads with a light outer band surrounding a dark circle, it's got fuel in it.

Answer 2

If the car has a mechanical fuel pump (which the 289 did have), please check that the diaphragm in the fuel pump is not leaking. When the pump is not used for a long spell, the rubber diaphragm can dry rot and crack, letting fuel into the crankcase. On a car that old, a new pump would probably be a good investment even if it isn't the cause of the leak.

Answer 3

More than likely, there's coolant getting into your motor oil versus fuel. And, there's no other fluids which could be getting into your oil.

Regardless if it looked milky when you changed the oil, what did the first part which drained out look like (or did you notice)? Oil is lighter than water/coolant, which means water would come out first when draining the oil.

As for fuel, I don't know of an easy way to tell other than what you've described ... however, a likely spot for fuel to be entering the engine on your 289 is at the fuel pump. If there's a problem with where the diaphragm is at, it could pump fuel right into the engine where it attaches (where the fuel pump arm goes up into the block to meet the cam). You could possibly take it off of the engine and check for signs of it leaking, or cobble something together to actuate it by hand to see if it's pushing fuel by there.

Answer 4

If an engine sits for a long time, some parts tend to take a memory or a "set"

Tyres can develop a slight flat spot, piston rings can get a bit stuck in their groove, and valves like the PCV system can stick a bit.

This may be a heisenproblem which goes away with a bit of time and some driving, along with the associated heat cycling.

If problems persist it may be worth taking an oil sample while its warm and stirred up, and sending that to an oil lab for an analysis.

Its also worth checking the radiator coolant height and seeing if that is going down faster than expected.

Answer 5

A probable reason: inaccurate measurement, either when filling or when checking later.

In an engine, oil has a great deal of cavities and surfaces to reside at for a while before going to the pan. This is even more pronounced for the fresh, cold oil from the factory bottle.

Because of this, it is rather easy to overfill the engine in the first place.

If a coolant gets mixed in the oil as much as visibly changing the oil level, you will see the coolant level getting down (beware when checking: the coolant level drpends on the temperature way more than the oil level)