Help With Cat 3406B Issues

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by OldRed98, Dec 26, 2020.

  1. Rideandrepair

    Rideandrepair Road Train Member

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    Low oil pressure is usually the rods and mains. They were recommended changed every 250k. Blow by probably the rings, though they may seal up after you run it a bit. Smoking when cold is normal. Very cold weather, really smoke and run very rough, till it’s warm. If it were me, I’d change the turbo, roll in new bearings. To avoid a disaster. Run it and see what you got. I’m not a mechanic, but I had a 1992 425C, It required bearings at 500k, which I had done. They’re great engines. King of the hill, back then. You’re gonna like the power, and especially the torque.
     
    Last edited: Dec 27, 2020
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  3. OldRed98

    OldRed98 Light Load Member

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    I suppose if I pull the pan then I could measure my bearing clearances. After warming the truck up 2 days in a row, the exhaust smoke has almost gone away when hot. The motor runs rather smooth and sounds good. I'm not going to run it anymore until I get the oil sample figured out just in case I have diluted oil.

    I'm excited to get this truck out and drive it a bit. I figured it would be a fun project and I'm hoping to get some miles in before a full inframe.
     
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  4. Rideandrepair

    Rideandrepair Road Train Member

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    Everyone swore by Shell Rotella on the Cats. When mine started using more oil, I tried Mobil for a couple changes. Some claimed it would slow oil consumption. It’s hard to say. Typically the oil pressures pretty high. I forget exactly, maybe 60. Higher on average than my Detroit’s. The other thing to watch is the Damper. They will go bad, and wobble. At an idle, it’s easily seen. Water pumps that seep from the weephole. Cat never really fixed that. Instead they put a piece of spongy plastic type plug in the hole. It just sits in there. You can pull it out with a pair of needle nose. After many claims of fixing the problem. Occasional minor seeping is considered normal.
     
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  5. Rideandrepair

    Rideandrepair Road Train Member

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    I’m assuming it’s a mechanical engine. Not a peec engine. Mine was a peec. It was a hybrid mechanical pump,controlled by a fuel cooled ecm. Only made for a few years, before the E model came out, around 1996. It was a real flop. Power was limited. The mechanicals could be turned up, by tweaking the fuel pump. Had to find a good Cat Mechanic to rebuild the pump. Not sure what they did exactly. But it involved the springs, I believe. But the power was amazing, easily out pull a 500 Detroit.The only other problem I can remember is exhaust manifold studs breaking. I ran mine for a few years, with 1 broken stud.
     
    Last edited: Dec 27, 2020
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  6. little cat 500

    little cat 500 Road Train Member

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    oil change no telling how long thats been in there
     
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  7. OldRed98

    OldRed98 Light Load Member

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    Yes its the all mechanical model out of an 86 W900. I didn't know about the Peec Motor. Picked this truck up for $9000. I sold a backhoe and I'm putting the money towards this truck. Figured I couldn't go wrong at that price and I was excited about owning a 3406B. I also enjoy restoring an old truck.


    @little cat 500 ... Good call on changing the oil. Despite being started a couple times at the auction.... This truck has been sitting a while. I'm curious to know if an oil change will help my oil pressure. Time to find a new turbo and change the oil.
     
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  8. AKDoug

    AKDoug Medium Load Member

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    Get a new gauge on it to confirm oil pressure. My 1988 3406B puts out 65psu at 65mph and idles at 40psi with 100K on a complete inframe. It also grey/white smokes at idle when started. It's done it since before the inframe, and before. Once warmed up it idles nice and clean.
     
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  9. OldRed98

    OldRed98 Light Load Member

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    Thank you! I was wondering where oil pressure should be on a fresh motor. I had a good 50PSI at Idle when cold. But after ideling/full temp... it dropped to 15-18PSI. It builds fine when I rev the motor but super low at hot idle. I could try my mechanical gauge kit as a backup to see if the dash gauge is accurate.
     
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  10. Rideandrepair

    Rideandrepair Road Train Member

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    What about oil temp? If the coolers plugged up, might be the cause. I think it should be about 20 degrees higher than coolant.
     
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  11. wore out

    wore out Numbered Classic

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    Rod and main bearings have a tell tale sign.......really good pressure cold that falls off drastically with heat.


    I have seen the timing advance on a B cause low oil pressure.....as well as most everything else mentioned.


    Blow by could be coolant in the oil easy as not and honestly is my first guess. I realize the oil isnt milky but coolant will steam out the blowby way before you can see it in the oil. Pull the back valve cover off....its easy enough to do. I would almost bet your gonna find rust from it sitting or sludge from it running.


    You can guess here and spend good money after bad......or take it a competent B model man and fix it. Notice I didn't say mechanic......even most CAT dealers #### these things up in this day and age
     
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