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Black Oil

drcarpdrcarp Posts: 9
edited March 8 in Chevrolet
I HAVE A 350 IN A 1986 S10 AND THE OIL IS A BLACK 500 MILES AFTER AN OIL CHANGE. THE TRUCK IS GEARED FOR 3000 RPM AT 60 MPH. THE MOST I DRIVE IS 16 MILES TO THE GOLF COURSE AND 5 OF THAT IS AT 60 MPH. THE REST IS IN TOWN. GAS MILEAGE IS 8 MPG. THE ENGINE IS RUNNING ABOUT 350 HP. WHERE IS THE CARBON COMING FROM TO DARKEN THE OIL. I CHANGE THE OIL VERY FREQUENTLY.

Comments

  • paisanpaisan Posts: 21,181
    Well my guess is that the tuning on the 350 in an S10 would be fairly aggressive, since the S10 was not offered with a 350 from the factory. Seems like it may be overheating.

    -mike
  • THANKS FOR THE REPLY MIKE
    THE TEMP.IS A LITTLE WARM AT START UP BUT ALWAYS RUNS 180-190 ON TEMP. GUAGE.
    K.C.
  • hoodlatchhoodlatch Mid-westPosts: 255
    Temp sounds great to me. Does the carb run rich or does it over-flow when you shut it down? After it sets for a few hours do you have to pump the accelerator several times to get it to fire up? I use to have a 350R with a four barrow that when I turned it off the carb would drain down allowing the gas to wash down the pistons and cylinders.

    Did you ever think about changing the ring and pinion to get better fuel mileage? Good luck :)
  • okko1okko1 Posts: 327
    what kind of carb are useing and what kinda air cleaner. sounds like a 3.73 gear. a 700r would help some on fuel. carburation equals carbon tell use more about the age and condition of the engine. does this engine use oil.
  • the carb may be rich but it starts without touching the accelerator. Rear end change may be an option later
    thanks for the reply
    k.c.
  • Carb is Edelbrock 1406 600 cfm electric choke. air cleaner is large 13-14" x 3 round no brand name. engine is about 3 years old since rebuild with 20 k miles engine doesn't use oil
    thanks for the reply
    k.c.
  • okko1okko1 Posts: 327
    thats a very good carb. is this an egr motor
  • No erg no smog no converter
    headers and dual exhaust
    thanks for the reply
    K.C.
  • hoodlatchhoodlatch Mid-westPosts: 255
    From the sound of things I wouldn't touch a thing. It seems your got it right where you want it. :)
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,838
    The only explanations I can think of for "black oil" is compression blow-by into the crankcase, fuel contamination of the oil from over-rich mixture, (and that gas in the oil doesn't burn off in a 16 mile trip), OR the air filter is letting in way too much dirt because it's not sealing right.

    You should check to see if your oil dipstick reads HIGHER after your short trip (wait 15 minutes after you stop).

    Excess fuel in your crankcase may be acting like a solvent all throughout your engine (this is not a good thing and must be corrected immediately).

    I'd suggest you treat your symptoms of black oil with the utmost seriousness until you track it down.

    Oil analysis might tell the story.

    MODERATOR

  • THANKS FOR THE REPLY
    WILL CHECK CARB MIXTURE SETTINGS AND TIMING TOMORROW.
    K.C.
  • okko1okko1 Posts: 327
    that carb your useing is pretty simple to change jets and metering rods in. there is kit for around 60.00 i think. be careful if the engine has a larger than stock cam that you don't get to lean. that carb with factory jets in good working order should be 90% efficient on any small block.
    are you getting any oil thru your pvc system or in the breather it's self
  • IT DOESN'T LOOK LIKE ANY OIL AROUND PVC AND THE BREATHER IS TIGHT AND CLEAN. I LEANED OUT THE CARB TODAY LET'S SEE IF THIS IS THE PROBLEM.THANKS FOR THE INFO
    K.C.
  • zaken1zaken1 Posts: 556
    Your gas mileage of only 8 mpg, along with black oil, tells me that the carb is way, way too rich. This amount of richness cannot be cleared up by just adjusting the idle mixture screws. It is either coming from 1> a float level that is set too high, or a float valve that doesn't shut off the fuel when the fuel reaches the correct level, or a float that is heavier than it should be (plastic float that has become porous and soaked up gasoline or a brass float that has a leak in it). 2> A choke plate that doesn't open fully when the engine warms up, or a choke pull off (also called choke vacuum break) that either has a ruptured diaphragm or is not getting any vacuum, or a choke pull off that is improperly adjusted, and doesn't pull the choke open far enough. or 3> clogged idle air bleeds or clogged main air bleeds, or air bleeds that are too small for this engine, or stuck metering rods, wrong size metering rods, or main jets that are way too large for this engine.

    Another thing to consider is that the distributor vacuum and centrifugal advance mechanisms must both be working properly, before the carb can be set. And the ignition system must be producing a spark of adequate intensity, while the spark plugs must not be misfiring or carbon fouled.

    But, in any case, the choke plate should open fully when the engine is warm, and if you look down into the carb air horn right after shutting off the engine, there should be no fuel spilling into the engine after it is shut off.

    If you have changed the compression ratio or the cam, then whatever jets came in the carb may be totally off for what the engine now needs. If your carb was not intended for the type of engine it is on, it may also be too rich for that reason. In those cases, you need to either get an exhaust gas analyzer and keep leaning out the jets and metering rods until the air fuel ratio reaches about 12-1 under heavy throttle, and about 14-1 to 15-1 under easy driving. Or take it to a performance shop that has a dynamometer, and have them blueprint the carb by running the truck on the dyno and monitoring the exhaust gas.

    If you are good with carbs and tuning, you can also do this by driving the vehicle, and reading the appearance of the spark plugs. But carbs have many different circuits with overlapping effects; so it is necessary to understand how these circuits work, in order to know which parts to adjust and what to change.

    I hope this information gets you on the track to fixing this problem. Let me know, if you have further questions.
  • wow thanks for the reply. i will follow up on these answers and let you know
    k.c.
  • hoodlatchhoodlatch Mid-westPosts: 255
    That answer was articulated well. Even I could understand it. Do you have any experiences on S-10 cruse control? :)
  • zaken1zaken1 Posts: 556
    Sorry, I only do fuel system and ignition tuning.
  • zaken1zaken1 Posts: 556
    I had a couple of additional thoughts that might speed up the process of sorting out this puzzle. Does the engine have a stock fuel pump? If the truck now has a fuel pump that puts out more pressure than the stock pump, the carb needle and seat may not be able to handle the increased pressure. In such a case, it is necessary to install an adjustable fuel pressure regulator between the pump and the carb. There is no need to spend big bucks for this item. Holley makes several adjustable pressure regulators which sell for less than $30. I would recommend their PN #12-803 'max pressure regulator.' It can be set to limit fuel pressure to any level between 4 1/2 and 9 psi.

    I also would like to know if any other modifications have been made to the engine. I'm particularly interested in any changes to the intake manifold, camshaft, cylinder heads, valve train, and pistons. You say it makes about 350HP; where did those numbers come from? Has the engine been dyno'd?

    Also, since the engine has 20,000 miles on it; has it been turning the oil black for that whole time, or has this just begun recently. If it only started happening recently, can you correlate it with any changes or new parts that have been installed? Has this carb been on the engine the whole time? And has the carb ever been taken apart?

    I'd appreciate any details you can provide.

    Thanks!
  • zaken1zaken1 Posts: 556
    K.C:

    When I woke up this morning, a light bulb lit up in my head: S10s made in 1986 and later all had fuel injection, and used an electric fuel pump which is mounted inside the gas tank. This pump produces over 30psi pressure. So, if it's still in place after your V-8 conversion, that high pressure fuel injection pump is just drowning your poor carb with excess fuel. The carb on your 350 engine is designed to work with 4 to 9psi fuel pressure. The fuel injection pump is putting out so much pressure that it wouldn't be practical to try reducing it with a pressure regulator. Instead, I would suggest simply removing the fuse for the S10's stock electric fuel pump, or disconnecting the power wire that goes to the pump at the gas tank. (Be sure you don't cut the wire for the fuel gauge, and that you insulate and secure the cut power wire, because it will still be electrically live.)

    If there is a mechanical fuel pump on the 350 engine, then it should be able to draw the fuel it needs through the disabled electric pump. But if you installed an electric pump anywhere that's higher than the tank, it may have trouble pulling fuel up to the engine. Electric pumps are made to push fuel, but they are not good at pulling fuel from a lower point.

    There are now lots of after-market electric pumps out there which produce very high pressure, and are made to be used with fuel injection systems. Those of us who have carburetors on our engines have to be careful not to use that kind of pump, because it will create severe flooding problems.
  • okko1okko1 Posts: 327
    IF HE IS USES THE EDELBROCK 600 WHICH I HAVE USED A NUMBER OF TIMES ON SMALL BLOCKS UP TO 400HP I HAVE HAD MY BEST LUCK AT ABOUT 4LBS. OF PRESSURE AND YOU CAN CHANGE JETS,SETUP SPRINGS,AND METERING RODS WITHOUT REMOVING THE CARB OR ANY LINKAGE.
  • zaken1zaken1 Posts: 556
    Thanks for the tips!
  • THERE IS A MECHANICAL PUMP ON THE TRUCK NOW. THIS WASN'T THE CASE A YEAR AGO. YOU ARE SO RIGHT ABOUT THE PUMP IN THE GAS TANK WHICH WAS REMOVED AFTER BLOWING A CARB.THE PUMP RUNS AROUND 4# PRESSURE. THANKS FOR ALL THE KNOWLEDGE COME ON DOWN TO LAKE OKEECHOBEE AND GO FISHING.
    THANKS TO ALL
    KENNY CURRAN
  • zaken1zaken1 Posts: 556
    Kenny,
    Sounds like we both have been on the same trail, but something still is going on to turn your oil black and suck all that fuel. If the mechanical fuel pump has a leak in the diaphragm, it can pump gasoline into the crankcase. This will make it look like the oil level is not going down, but the oil is gradually being replaced by gasoline. In that kind of situation, I've seen an engine blow the valve covers off when the gas in the oil exploded. If you unbolt the pump from the block, it may be possible to spot a leak; if you can see or smell any gas on the engine side of the mounting flange. Or, you can substitute a low pressure electric fuel pump for the mechanical one, and see if the problem goes away.

    One other possibility is that someone left out the check ball, and/or the weight in the accelerator pump discharge nozzle. This would make the pump nozzle act as a siphon, and pour fuel into the engine when it was running. If you take off the air cleaner and look into the carb with the engine speed held steady at about 2500 RPM, there should be no fuel coming from the pump nozzle, unless you speed the engine up.

    And, of course, it there is a sound insulating blanket on the underside of the hood, and it is too close to the air cleaner or it is loose; it can be pulled against the air cleaner by the force of the incoming air; which makes it act like a choke that is on all the time.

    When I used to live in Kissimmee, I would have been happy to drive down there and go fishing, but since I moved back to California after the hurricanes began, it's now too long a drive.

    Joel
  • zaken1zaken1 Posts: 556
    Kenny,
    Along with the points I raised in the preceding post, there is one other test that's worth doing. With the engine off, take off the covers over the metering rod assemblies, and note the height of the top of the rods. Then start the engine, and see if the rods move to a lower position when the engine idles.

    If the metering rod assemblies are always in the up position when the engine is running, then the carb will supply the richest possible mixture at all times; and this will grossly overfeed the engine with fuel.

    If the rods did not move down, then they are either stuck, or the rod control pistons are not getting any vacuum. If you can press down on the top of the rods, and they move down easily against their spring, then they are not stuck. In that case, the vacuum passage to the piston well is blocked; either by gasket cement, or by an incorrect or improperly positioned carb mounting flange gasket.

    Joel
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,838
    Whatever he does he'd better do it quickly. Having gasoline washing your cylinder walls and bearings is NOT GOOD! This could end up being a relatively low mileage engine.

    MODERATOR

This discussion has been closed.