Fuel Dilution of Crankase Oil

[Stuart F.]

What are the hazards/dangers of fuel dilution of crankcase oil, and at what point/level does it become so?

I have been experimenting with various ways to reduce or curtail fuel boil/perculation in heat soak after shut down (stinky 340hp w/AFB). The smell of fuel caused my local Auto Parts store to refuse my last drain oil, and I changed out my Rotella T yesterday to make sure I don't have trouble on a trip to a show today.

Any specific advice on this would be appreciated. I know the dangers of Hydraulic lock, but what else must I be concerned for?

Stu Fox

[Jim T.]

Re: Fuel Dilution of Crankase Oil

Stuart I do not have any answer to your question, but for used oil disposal I have also used Wal-Mart. Do not know if they still do since other places are now closer to home, but EXXON stations that service cars used to take any oil after the Alaska mishap.

[Steven S.]

Re: Fuel Dilution of Crankase Oil

I had a 327 that got fuel into the oil that was run unaware and ended up with low oil pressure and a bad cam, so I had assumed that the dilution of the oil was the cause of these problems.

Steve

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

this what blew up a lot of 3 X 2 427 BB because the carbs bled thru diluting the oil .

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

What are the hazards/dangers of fuel dilution of crankcase oil, and at what point/level does it become so?

I have been experimenting with various ways to reduce or curtail fuel boil/perculation in heat soak after shut down (stinky 340hp w/AFB). The smell of fuel caused my local Auto Parts store to refuse my last drain oil, and I changed out my Rotella T yesterday to make sure I don't have trouble on a trip to a show today.

Any specific advice on this would be appreciated. I know the dangers of Hydraulic lock, but what else must I be concerned for?

Stu Fox

the best solution to fuel boiling in the carb is to block the exhaust heat riser crossover passage in the aluminum intake with stainless steel shim stock and make sure you wire open the heat riser valve.

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

if you have a "take apart" fuel pump drill a .015 hole in the plate that holds the valves so the pressure between the fuel pump and the carb will bleed back to the inlet side of the pump when you shut off the engine and reduce the pressure on the needle/seats in the carb

[Bill M.]

Re: Fuel Dilution of Crankase Oil

What are the hazards/dangers of fuel dilution of crankcase oil, and at what point/level does it become so?

I have been experimenting with various ways to reduce or curtail fuel boil/perculation in heat soak after shut down (stinky 340hp w/AFB). The smell of fuel caused my local Auto Parts store to refuse my last drain oil, and I changed out my Rotella T yesterday to make sure I don't have trouble on a trip to a show today.

Any specific advice on this would be appreciated. I know the dangers of Hydraulic lock, but what else must I be concerned for?

Stu Fox

The 300SLs had a fuel dilution problem due to their direct cylinder injection. Do a search on those key words. I just found a recommendation that dilution not exceed 5%.

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

The 300SLs had a fuel dilution problem due to their direct cylinder injection. Do a search on those key words. I just found a recommendation that dilution not exceed 5%.

they had a dry sump with lots of oil to dilute i believe. i also wonder what weight oil they used in those engines

[Bob S.]

Re: Fuel Dilution of Crankase Oil





The one on the L-79 was installed between the stock mechanical fuel pump and the carb inlet, the one on the Cobra was installed at the fuel tank outlet (on the suction side of the mechanical fuel pump).



Regards,
Bob S.

[Bob S.]

Re: Fuel Dilution of Crankase Oil

Others here can probably speak to this better than I, but engine manufacturers (both gasoline and diesel) have gone to great lengths to reduce / minimize lube oil dilution; both for the obvious reason of the detrimental effect it has on oil life and the potential for causing engine problems, but also as a source of polution.

Bob S.

[Stuart F.]

Re: Fuel Dilution of Crankase Oil

Thanks fellows. I am at wits end right now. I went to our local Octobervettesfest show today in Kissimmee (about a 25 mile drive on the highway). It seemed to run fine going over, but I was lollygaging behind my son at 55 mph. On the return trip, I led and left him as I was pacing a C-5 on the way back at 75-80 mph. When I got home, I popped the hood, removed the air cleaner and let it sit outside. Within about 5 minutes it was streaming gas full force - this time out of the accelerator nozzles! I left it outside until it stopped puking, then got it started and drove it in the garage where it now sits stinking to high heaven. So now I've seen it coming out of the venturi tubes (thru the main jets) and the accelerator pump nozzles (pump circuit).

Your danger warnings about the oil dilution sound ominus.

I think it is time to yank the manifold and see what gives. There goes my "engines never been apart" boast. Perhaps it is time to pay attention to my I.R. Readings. My RH exhaust manifold continues to run 50 degrees hotter than the LH at the center 2 ports, even with the heat riser wired open. Something isn't right and I am treating symptoms instead of the cause.

Stu Fox

[Bill M.]

Re: Fuel Dilution of Crankase Oil

they had a dry sump with lots of oil to dilute i believe.

10 liters in a separate oil tank. The level of the oil in the tank could rise due to dilution.

[Joe R.]

Re: Fuel Dilution of Crankase Oil

Stu,

You have problems that need fixing that goes back to the overheating situation. First, I have had many 340HP 63's and none of them ever gave any trouble with gasoline dilution. AFB's are excellent carbs and with a good needle and seat should never leak any gas into the manifold under normal operating.

1. Make sure that your heat riser is operating properly.
2. Take off the intake manifold and block the heat riser passages.
3. Buy you a rebuild kit for the AFB and change out the needle and seat.
4. Check your fuel pump pressure.
5. Make sure no fuel lines are close to the block or heads.
6. Check the operating temperature of the radiator.
7. Replace the thermostat with a 180 degree when the manifold is off.
8. Check your timing.

You do those things and you should have no problem with dumping gas down the manifold ever, anytime, anywhere!!!!

Regards,

JR

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

like i have posted before pressure test the seal between the needle/seat and the carb top as a lot of kits have these gaskets with too large a inside diameter hole and do not seal well. after you shut off the engine fuel leaks pass these gaskets and overfills the float bowls. drilling the .015 hole in the fuel pump valve plate works as i did that to a lot of the older 2 X 4 carb corvette engines that flooded after shut down.

[Stuart F.]

Re: Fuel Dilution of Crankase Oil

Joe;

Thanks for your input. I appreciate it specially from your having experience with 63 340 hp engines. In response to your points, let me amplify on what I have done to date;

1) I have the heat riser butterfly wired open right now. It worked fine before when I first started having this problem at an acute level (it always did some before).

2) I may try a temporary blocking of the riser passages in the manner we used to do it "Back in the Day", i.e. cut plates from large coffee can using new gasket set as template. We used that due to the rolled lip which you could bend over to fashion a handle of sorts. Pound them flat and file the leading edge to near knife sharp. Loosen just the two manifold bolts to either side of the riser passages, then work them down between the head and the gasket until the bent over lip seats on the manifold, then retighten the bolts. Granted, those engines were not near as old and perhaps the gaskets hadn't taken a permanent set. In this case, if I were to encounter too much resistance, I would not force the issue.

3) I am experimenting using two different carbs that I recently rehabbed. One has new needle/seats and the other Tomco inlet valves. Both, when installed, were tested with compressed air and soapy water to ensure the integrity of the seats and gaskets. I have tried lower float settings (as much as down to 5/16" from standard 7/32"). I currently have a "sandwich" base gasket consisting of 2 SS plates from the L-75 and 2 gaskets. None of my carburetor changes has proved effective.

4) I have tested my fuel pump pressure (between the filter and carb) and it is a little under 6 psi (std. AFB N/S supposed to be good @ 6.5 psi).

5) Other than currently using fuel hose between filter and carb, all other fuel lines are standard steel or chromed steel. The filter is still mounted on the water manifold (as standard) and shows the same temperature as the manifold (+180*) after shut down, or too hot to touch.

6) I.R. temperature tests of the radiator look to be normal during operation and after shut down.

7) I currently have a 160* thermostat (always used). I.R. temp tests upstream and downstream of the thermostat look as expected during operation (have not recorded after shut down temps, but they looked normal as I recall).

8) I am using a 236 (B29) VAC (recently installed) and 12* initial, with modified (faster mech advance curve). I did not have such an acute problem b4 installing #236 VAC, but theoretically that should have helped by giving more consistent (full) vacuum advance at idle and low speed.

I spoke with 2 other 340 hp 63 owners yesterday at the show, and neither has had such a severe problem. One uses avgas regularly, and the other TEL (Max 2000). I normally use the latter as well, but did not add any last fill as it was only a half tank of BP 93 octane no lead. It has been primarily with this last tank that I have had the problem, but again theoretically, the TEL should not make a difference if the 10% ethenol is the culprit.

Today I will do my normal fill of ExxonMobil 93 + TEL and see where we are at.

Thanks again for your input. If I ever find a way to curtail this problem, I will certainly post the results - even if it is from my own stupidity.

Stu Fox