Fuel Dilution of Crankase Oil

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

you need to use stainless steel shim stock as the coffee can tin will burn thru after a while. the easy way to install the shim stock is drain down the rad loosen all the manifold bolts and slip in the shim stock. done lots like that with no prblems. i would do the drilling of the fuel pump valve plate first as that will remove all pressure from between the fuel pump and carb when you shut off the engine. this why all later GM engines have the return line to the fuel tank from the fuel pump

[Stuart F.]

Re: Fuel Dilution of Crankase Oil

Clem;

Thanks for your advice on the shim stock vs. the coffee cans. I guess we got away with that up in Wisconsin as we only did it during the summer months. We pulled them out about this time (fall) and normally ran fuelie gaskets with the oval holes otherwise.

I did test the installed needle/seats per your instructions and, in fact replaced gaskets on one set before hand that seemed too loose. As installed in either carb (my A or B), both passed the test with compressed air and using the soapy water.

I will get out my spare fuel pump today and see if I can do the mod you suggest. I had run this one long ago and have a rebuild kit that I have been looking for a reason to install. Besides, I havn't used my spring loaded bolt in many years, but I know where it is. I also have to remember to plug the fuel hose to the pump for, as I recall if parked on the level, this line is lower than the tank. Guess I will hold off on my next fill up.

Thanks for your valuable support. I'll keep you posted on my findings.

Stu fox

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

Clem;

Thanks for your advice on the shim stock vs. the coffee cans. I guess we got away with that up in Wisconsin as we only did it during the summer months. We pulled them out about this time (fall) and normally ran fuelie gaskets with the oval holes otherwise.

I did test the installed needle/seats per your instructions and, in fact replaced gaskets on one set before hand that seemed too loose. As installed in either carb (my A or B), both passed the test with compressed air and using the soapy water.

I will get out my spare fuel pump today and see if I can do the mod you suggest. I had run this one long ago and have a rebuild kit that I have been looking for a reason to install. Besides, I havn't used my spring loaded bolt in many years, but I know where it is. I also have to remember to plug the fuel hose to the pump for, as I recall if parked on the level, this line is lower than the tank. Guess I will hold off on my next fill up.

Thanks for your valuable support. I'll keep you posted on my findings.

Stu fox

any time you do fuel pump work PLUG the fuel line from the tank. i had a co worker whose wife was killed when she turned on the light in the garage after her son had removed the fuel pump from his car and went to the auto parts to get a new one. the gas fumes exploded and she was burned so bad she died several days later. gasoline fumes are nothing to fool with as that is the second acquaintance that had this happen with fatal results.

[Gerard F.]

Re: Fuel Dilution of Crankase Oil

Stu,

I think you need to insure that there is no pressure in the fuel line, pump to carb, after you shut down. Maybe it is a check valve in the filter, or the fuel pump valves are holding more than they should.

Clem has probably the best solution to drain the fuel lines back to the tank. But if there is any pressure in the tank, it will act as a reservoir and continue to feed fuel to the carb with little relief in pressure vs volume.

So check the gas cap after a hot run. Is the PRV cap you have, a pressure relief or pressure reducing valve. Try the same run with an original type cap.

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

Stu,

I think you need to insure that there is no pressure in the fuel line, pump to carb, after you shut down. Maybe it is a check valve in the filter, or the fuel pump valves are holding more than they should.

Clem has probably the best solution to drain the fuel lines back to the tank. But if there is any pressure in the tank, it will act as a reservoir and continue to feed fuel to the carb with little relief in pressure vs volume.

So check the gas cap after a hot run. Is the PRV cap you have, a pressure relief or pressure reducing valve. Try the same run with an original type cap.

that was the problem with the 3 X 2 setups as the mufflers heated up the gas tank and built up pressure so we drilled a 1/8" hole in the gas cap to let out the pressure.

[Stuart F.]

Re: Fuel Dilution of Crankase Oil

Jerry and Clem;

Boy! I like that idea. That's an easy one. I just went out and covered the car up (put to bed to sleep for a while) as I was very discouraged, but checking the cap on the tank is certainly worth a try. The new cap on there now is the one Chevy sells as a replacement for the 63,
p/no. 3952708. I understood it was a 2-way PRV, but I will put the original vented cap back on and give it a try.

Thanks for the idea.

Stu Fox

[Edward B.]

Re: Fuel Dilution of Crankase Oil

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

300SL oil system has a maximum quantity of 15 liters which includes the dry sump and oil cooler. For non-competition use many by-pass the oil cooler so as to raise the oil temperature and evaporate some of the gasoline that has made its way into the oil. If the idle oil pressure is kept over 30psi the system works as designed and oil dilution is kept to a minimum. Best preventive maintenance is frequent oil changes (<2500 miles) and the use of a quality CJ-4 oil. I'm now with Rotella T 15W-40 and have had no problems with crakcase dilution over 44 years of driving my 300SL.

[Edward B.]

Re: Fuel Dilution of Crankase Oil

I should also add that Bill Mashinter's father was one of the best known and most talented persons to ever work on 300SL fuel injection systems. He rebuilt a pump for my mother's 300SL Roadster in 1979 and it is going strong to this day. His treatise on the Bosch fuel injection system is a must to this day in the library of anyone who works on these cars.

[Stuart F.]

Re: Fuel Dilution of Crankase Oil

Ed;

If I were to try and translate your 300SL experiences to my situatiion, do you suppose if I drove more highway miles at a sustained speed I would recreate the higher oil temperature and pressure to evaporate some of the fuel from my crankcase? I too use Shell Rotella-T 15w-40 oil and, when before I changed it the other day, it was close to being water thin (not good!). I know that because it dripped off the dip stick. Also, it may have been my imagination, but the tappets sounded louder and I just re-adjusted them about a month or so ago.

Stu Fox

[Gerard F.]

Re: Fuel Dilution of Crankase Oil

Stu,

If you put your original gas cap on, make sure the vent valve works. If you shake it, you should hear the valve rattle inside. Also try to blow air through it from the inside in a horizontal position.

If you put a heavy magnet on top of the cap, the valve should open.

[Stuart F.]

Re: Fuel Dilution of Crankase Oil

Jerry;

Are you sure the 63 has a "Vent Valve"? When I poke a pin through the hole, it bottoms out at a depth that to me seems like it is contacting the inside of the cover, or about 1/2".

Perhaps what you are referring to as the "Vent Valve" is what others call a PRV (Pressure Relief Valve), which I understand the cap so equipped is what they replaced the 63 (and all other years that use the vented cap) with. The new cap I have has a lip around the vent hole like a tube (not on my original) and you can see what looks like a disc inside slightly below the inner surface. My pin will only go in about 1/8th inch on that one.

Still, I will pressure test both with compressed air to make sure they are clear. I am reluctant to drill the vent hole larger on my original, but may try it on my locking cap and try that.

Thanks again for your ideas and help. They are much appreciated.

Stu

[Gerard F.]

Re: Fuel Dilution of Crankase Oil

Stu,

You are right, the original 63 caps did not have the vent valve, they just had a vent hole which vented to the underside of the cap. All replacements and later years had the simple relief valve which vented both ways.

The replacement ones rattle when you shake them (if the valve is not stuck) and it shouldn't take much pressure to blow air through the bottom.

No need to drill holes in your original. I think Clem was taking about the caps with the valve (which can sometimes stick), where they would drill a hole right through the top of the cap and diaphragm.

Try your test with the original cap, if you can blow air through the hole.

[Clem Z.]

Re: Fuel Dilution of Crankase Oil

Stu,

You are right, the original 63 caps did not have the vent valve, they just had a vent hole which vented to the underside of the cap. All replacements and later years had the simple relief valve which vented both ways.

The replacement ones rattle when you shake them (if the valve is not stuck) and it shouldn't take much pressure to blow air through the bottom.

No need to drill holes in your original. I think Clem was taking about the caps with the valve (which can sometimes stick), where they would drill a hole right through the top of the cap and diaphragm.

Try your test with the original cap, if you can blow air through the hole.

to test if the tank is building pressure is your problem just remove the cap as soon as you get home and leave it off and see if the flooding stops. on the 3 X 2 corvettes you could hear the 'woosh" as you remove the cap.

[Bill M.]

Re: Fuel Dilution of Crankase Oil

I should also add that Bill Mashinter's father was one of the best known and most talented persons to ever work on 300SL fuel injection systems. He rebuilt a pump for my mother's 300SL Roadster in 1979 and it is going strong to this day. His treatise on the Bosch fuel injection system is a must to this day in the library of anyone who works on these cars.

Thanks. He was a fuel injection expert. I am not. I wish he were still around to help me restore the '59 fuelie that he bought new!

[Edward B.]

Re: Fuel Dilution of Crankase Oil

Stu: My knowledge of Corvette FI is next to nothing, but if your oil is as thin as you say, evaporation is not the solution to the problem. With the 300SL we are talking about relatively small amounts of gasoline (if everything is working properly) in a very large capacity system. You are dealing with 5 quarts of oil which already seems extremely comprimised and well beyond the point of evaporative cleansing. If it were a 300SL, I would not drive it until the malfunction in the fuel system that is causing the dilution is identified and corrected.