Gas in the oil

I have 2003 Mercury Grand Marquis with 72,000 miles on it. I have been using Amsoil 0W-20 oil with an Amsoil bypass filter system since it was new. The oil and filters are changed when the oil analysis says it needs to be changed. The oil is analyzed every 5,000 to 7,500 miles with oil and filters changes usually occurring around 20,000 to 25,000 miles.

The last analysis at 70,000 miles said that there was fuel in the oil and it needed to be changed and the problem corrected. The oil and both filters were promptly changed but no one has come up with a probable cause for the fuel to get into the oil.

Years ago when cars had mechanical fuel pumps and carburetors, this was a common problem. The diaphragm in the fuel pump would rupture and allow gas to run down the actuating arm to the cam shaft and into the oil. This is not the case with this car as it has an electric fuel pump and fuel injection.

The best anyone has come up with is that gas in running from the cylinder, past the rings and into the crankcase. This is doubtful because: 1) A compression test shows 160 to 170 pounds on each cylinder and the engine uses no oil between changes. 2) A diagnostics on the fuel system shows no problem. System holds pressure and has no leaks. 3) The car runs beautifully. Fuel mileage is 19 city and 25 highway. At an idle it?s so smooth that you would think the engine quit. 4) No one can explain how gas gets into the cylinders in the first place. As I understand it, the injectors are located in the intake manifold near the intake valve. The injectors are not leaking and the intake valve is closed when the engine is not running.

Any ideas?

There are only two areas where gasoline can enter a fuel injected engine where it contminates the oil. These are leaking fuel injectors or a leaking fuel pressure regulator.

Start the engine and let it idle for a minute or two. Shut the engine off and remove the vacuum hose from the fuel pressure regulator. It gas leaks out of this connection, that’s how the gas in entering the engine and contaminating the oil.


Third area: Badly misfiring engine.

Long short fourth area: evaporitive emissions system with liquid gasoline where there should only be vapors.

You’re the first logical idea that I have heard. Even the Ford dealer didn’t suggest this.

I don’t have a shop manual (in fact I don’s think they make one) so how do I locate the fuel pressure regulator? Can I reach from under the hood?

With no pressure leaks I’m inclined to think this problem could be a result of subtle misfires (which may not set a code or even be noticeable) and overanalyzing of the engine oil.
I think having oil analyzed to determine if it needs to be changed is odd at best.

Those oil change intervals you use are not good on the engine considering the age and miles total on the car. That is reflected in the compression readings which are going downhill and should be up in the 190 range.

Recheck those compression readings with a wet test and I think you will find they will shoot up to about 200. At that point you can kiss the piston rings goodbye and blame it on 25k mile oil change intervals.

A leaking regulator should result in a poorly running engine.

The schedule calls for the plugs to be changed at 100K miles. I bet they need to be changed now, even if it is only 72K miles.

It is unlikely that your fuel regulator diaphragm is leaking since you mentioned that the fuel system is holding pressure after shut off.

Is it parked outside, in the cold? Do you take short trips? That combination would allow blowby (from one of the reasons above, or just from it being cold) to accumulate condensed oil. A friend was able to light his oil with a match because of the condensed blowby.

I concur with ok4450.
Probably the saddest part of this scenario is that, for the price of all those engine oil analyses and that expensive synthetic oil, the OP could have done 4k-5k oil changes with conventional oil and wound up with far less engine wear than he got with his approach to maintenance.

As mountainbike, one of our other very valuable members likes to say, the idea is to extend the life of the engine, not the life of the oil!

Synthetic oil has some advantages, particularly if you live in an area with extreme temperatures, but running an engine for 20-25k between changes is…just not smart…no matter what type of oil one is using.

A sticky thermostat could extend the time it runs open loop and rich.
I recommend changing the (cheap conventional) thermostat every 4-5 years.

This car has a cylinder compression issue which could very well be contributing to the oil analysis problem and until that is resolved one can throw every part in the bin at it without accomplishing anything.

An engine with lower compression may appear (key word) to run fine and may idle like a Rolex watch as long as the readings are in the same general area. Add one or two of them at 190 or 140 into the mix with the 160s and the idle may become slightly rough although it may still appear to run fine when the throttle is opened.

It’s also quite possible for an engine to have lowered compression and use no oil and vice-versa. As to the versa, how about a Subaru with 185 across the board and (seriously) burning through a quart per 5 miles.

Phranque; You saved a few quarts of oil (11 oil changes of 4.5quarts each=49 quarts, probably worth about $150!! By doing that you operated the vehicle contrary to the manufacturer’s recommendations, and caused about 300,000 miles worth of EXTRA WEAR!

So by saving $150 in oil and filters, you sacrificed 60% of a $5000 engine, or $3000.

I would like to meet you oil “analyzer”, and what he measures in your oil. Your car is in severe service, meaning the additives get depleted earlier, and sludging is rampant; and we would normally recommend changing oil every 5000 miles at least, not use synthetic oil, and use a block heater in the winter.

Amsol 0W20 is an extremely thin and slippery oil, and while it protects the surfaces, it does allow raw fuel to enter the oil sump when injectors leak or a very rich mixture in a carbureted engine allow both blowby and fuel leakage.

As mentioned by others, the way to make this very tough car last is to:

  1. Don’t use synthetic oil, if you must, use a 0W30 semi-synthetic, (Not Amsol)

  2. Change oil and filter every 5000 miles maximum, and stick to 5W30 dino oil.

  3. Use a block heater in the winter if you live in a cold area

  4. Take the car out for a fast highwy drive once a week or so if you do mostly stop and go city driving.

  5. If you analyze your oil, use a well known lab and measure acidity, metal wear, sludge, water, glycol, additive depletion, etc.

I’d personally disagree with always using dino oil and not using Amsoil. Nothing wrong with Amsoil. (except the price maybe) There are plenty of good synthetics that are cheaper.

But I’d agree that it’s pointless to go so long between oil changes to save a few bucks, while spending >$25 per oil analysis. What’s the benefit? Unless you like running a science experiment or consider it being “green” I guess…

This particular Ford can use just about any oil, as long as it is the right viscosity. I assumed OP wanted to save money by buying very expensive oil (I went through an Amsol pitch last week) and leaving it in a long time, not realizing that Amsol has no more anti-sludging and other additives than inexpensive dino oil. That purple coloring must be very expensive.

I would personally use 0W30 synthetic in the winter and change at 5000 miles and switch to 5W30 dino in the summer with the same chage interval. I would also use a block heater if parking outside.

There are many posters here who have gotten 300,000-400,000 trouble-free miles out of their Crown Vics and Grand Marquis while just using Walmart dino oil.

“That purple coloring must be very expensive” --Amsoil doesn’t use purple coloring. Are you thinking of ‘Royal Purple’?

Phranque…There is a web-site called “” where lubrication obsessive / compulsives meet and discuss issues like this…

Small amounts of gasoline that find it’s way into the crankcase evaporate almost instantly in the hot oil and are removed by the PCV system…A measurable amount of gasoline will cause the oil level to rise on the dipstick…

Other than the reasons Tester mentioned, the only way a detectable amount of gasoline can get into the oil is driving during extremely cold weather and not driving long enough to allow the engine to completely warm up, at LEAST a half an hour…In these conditions, a small amount of gas can wash down the cylinder walls and into the crankcase unburned…

Yes, this thought occurred to me, too. Although my other two cars are driven in much the same way and their analysis was clean. One other suggestion was that the analysis itself was in error. It?s almost time for another analysis so we?ll see what happens then.

Thanks to all of you.

I wouldn’t become too enamored with this car considering the compression readings. They’re already heading downhill and who knows where they will be in the next 25k miles.

You are right; but the amount of advertising Amsol uses relative to their sales volume has to make the stuff expensive. And I don’t believe they actualy spent the money for proper API certification. That costs $50,000 for each test.