Gmc topkick mystery tank under driver side step

WoodCutr

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I've got a 92 topkick with the 3116 cat, found a mystery tank under drivers door step next to the fuel filter and air dryer, anyone know what it is?

It seems both hoses go to the block and oilpan, one has a pressure sender/switch it looks like

Has a big oil leak and I have to keep cardboard under it when parked, trying to clean this truck up
 

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No idea. Looks like it’s banded like a filter housing though. Might be another one of Cat’s brilliant ideas that doesn’t make sense to anyone but them
 
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  • #3
thats definitely a thought, seems like it would come apart, looking at other topkicks and I cant seem to find one with this tank thing, its usually just a box right there enclosing everything under the step
I called the local cat dealer, and a big truck mechanic in town, google and sqwerl, nobody has a single clue what it is, and im scared to take hoses off to fix the leaks if its got pressure in it
I will continue the googling!
 
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  • #5
After market oil filter is my guess. Air breaks?
air brakes, yes, but not related to this "filter tube thingimajig"
google doesnt show anything about it being an oil filter, supposed to hold 6.6 gallons, I got under 5 gallons out of the motor last week, and it wasnt that low on the dipstick, so I doubt a filter since it would hold extra
 
The tank itself doesn't seem to see much pressure. That looks like only a thin stamped steel plate. You can see some accidental bends in it which can not append on a heavy gauge wall. Plus, on the second pic, the big collar around it is the kind made to hold together two half embossed parts with a gasket in between. Definitively not high pressure.
But nothing tells how and at what the hoses are connected inside. It could be a high flow filter, a heat exchanger (probably not, it should have two big hoses more), or a low pressure adjustable volume tank with a membrane inside (for example, a closed circuit able to handle some volume variations, but without the air/oil mixing found in a regular oil tank).
Just gessing.
 
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  • #8
so, it has been determined that it gets warm ish with the engine, im thinking what Marc said, maybe to even out oil pressure, the truck stays at 50psi hot or cold
 
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  • #9
got side tracked from oil leaks today, got the throttle adjusted so its getting around 100% instead of the 50-60% it had before, and got the trans modulator cable fixed so no more transmission/torque converter roasting going on hopefully
man this truck is a rocket unloaded and actually getting full throttle! 10 second zero to 30 (ok, not that slow, but not much better, caps at 55 ish)
 
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