- 737
- 1,373
- 93
- Location
- Mesa, Colorado
Hot oil idle pressure is about 16ish now
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What have you done to your FMTV or LMTV today
- Thread starter Coffey1
- Start date
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
I assume the expectation is that psi would be higher with a new pump? Or is that normal? I'm no expert.
If not , my logic tells me either I got a pump without the upgraded bypass Springs, OR, there's temp-related blow-by somewhere else. I'm going to
test psi at the inlet to the Amsoil bypass filter to see. Can worn rings or a defective HEUI pump cause that kind of pressure loss at temperature?
- 1,853
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- Portland, OR
Mine has never dropped below 20 psi no matter how hot I have got it. But is a C7 and technically the pumps are different part numbers. They basically the same in design.
Where did the pump you installed come from? I hate the prices and being bent over a sales counter in public (how rude), but the CAT dealer is the only source I feel I can trust to not rebox some third world replica.
When you are talking about pressure right off the pump - the only thing that effects that is the pump itself or the *restriction* provided by the clearances in the engine. Pressure is an effect of restriction to flow. *usually* changing the pump in an engine with low oil pressure is magical thinking. However in the SPECIFIC case of the 3126/C7 there seems to be some issues surrounding the pump internals and bypass valve (built into the pump) that cause pressure drops. But in the VAST MAJORITY of engines - pressure will not improve by simply changing the pump unless the new pump has a higher *volume* that can work against large clearances not providing enough restriction to flow.
That all said - the rule of thumb for oil pressure is 10 psi per 1000 rpm of engine operation at a minimum. And oil clearances are generally about 0.001" for each inch of journal diameter. If you go down the rabbit hole of why these numbers and not something else you find that much of this is far too complex to even model it in software and these numbers are from over a hundred years of trial and error.... for the most part.
Where did the pump you installed come from? I hate the prices and being bent over a sales counter in public (how rude), but the CAT dealer is the only source I feel I can trust to not rebox some third world replica.
When you are talking about pressure right off the pump - the only thing that effects that is the pump itself or the *restriction* provided by the clearances in the engine. Pressure is an effect of restriction to flow. *usually* changing the pump in an engine with low oil pressure is magical thinking. However in the SPECIFIC case of the 3126/C7 there seems to be some issues surrounding the pump internals and bypass valve (built into the pump) that cause pressure drops. But in the VAST MAJORITY of engines - pressure will not improve by simply changing the pump unless the new pump has a higher *volume* that can work against large clearances not providing enough restriction to flow.
That all said - the rule of thumb for oil pressure is 10 psi per 1000 rpm of engine operation at a minimum. And oil clearances are generally about 0.001" for each inch of journal diameter. If you go down the rabbit hole of why these numbers and not something else you find that much of this is far too complex to even model it in software and these numbers are from over a hundred years of trial and error.... for the most part.
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- 486
- 793
- 93
- Location
- Texas Hill Country
That appears to be within the specification for a CAT 3126b.
Minimum spec for 700rpm appears to be about 11psi. 16psi is 50% over minimum, 20psi is 90%.
I am more interested in what pressure we have at 1,600rpm, 30psi would make me very nervous at 1,600. Yours appears to be about 45psi near 1,600rpm—
Minimum spec for 700rpm appears to be about 11psi. 16psi is 50% over minimum, 20psi is 90%.
I am more interested in what pressure we have at 1,600rpm, 30psi would make me very nervous at 1,600. Yours appears to be about 45psi near 1,600rpm—
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
Interesting and logical. This engine is definitely an oil burner. So more wear on bearings all around could account for a 5-10psi loss? The new pump is pushing above 60, above 2000rpm so it's a noticeable change. The pump is a new cat part from wagner. Hence the expense at ~$1700. I also have the reman from cat for ~$700 as a spare bc I gave them the old core.
my gut is telling me the engine is just worn. Was burning a gallon per 3k miles previously.
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
Good curve! I'm always below the mid point of the acceptable range except for occasional bursts above 60. General driving between 1400-2000 is always above 45. It's going to get run to failure at this point. Maybe it's just not been run in at load ever? I did load tests on Gen's for years before graduating college and those would spew oil for an hour before settling in.
- 7,599
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- 113
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- Charlotte NC
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If it's burning oil at that rate - I would almost bet the low oil pressure is because of engine wear.
- 1,853
- 4,888
- 113
- Location
- Portland, OR
I can't disagree with that analysis. That is a pretty high rate of oil consumption. My C7 is definitely less than half that. I just topped it off the other day - about 2k miles on this oil change. Took a quart more or less.
You do know not to fill them to the full mark right? That last two quarts will just end up lubricating your leaf springs. The breather setup on these engines sucks and CAT redesigned it but the new version won't fit under our cab.
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
I didn't know that. I can drain some to pull it down. That dipstick range is about 3/16" wide
- 1,853
- 4,888
- 113
- Location
- Portland, OR
I keep mine halfway between low and full. That's about 2 quarts lower than "full"........ although now that I'm thinking about it, it's probably not nearly as much of an issue now with the ECO hubs. Original gearing had the engine taching so hard at 60 MPH it would vomit oil down the drivers slobber tube.
aw113sgte
Well-known member
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- La Crosse, WI
Picked up some new shoes 
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
aw113sgte
Well-known member
- 549
- 813
- 93
- Location
- La Crosse, WI
What are you talking about the rims are 20" and the tires are 20"? Just a tiny bit of rubbing.Not truc
not trying to burst your bubble but those tires don't fit that truck bro
Third From Texas
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Nothing you can't fix with some wheel spacers and a grinder....
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
At 200F after a 45min drive, I'm at 15psi, while dash gauge reads zeroish. So it's above the minimum at least.
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- 486
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- 93
- Location
- Texas Hill Country
"Zeroish" makes me nervous—
aw113sgte
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- La Crosse, WI
Changing some tires, replaced the drag link. Got myself an air hammer and it's my new favorite tool, popped the drag link tapers right out! Next to try it on those large torque rods....
- 737
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- 93
- Location
- Mesa, Colorado
I figured you for an in-ground pool guy.
Ronmar
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Any oil idiot light? Forget if yours is controlled by the ECU or a standalone pressure sw.
- 737
- 1,373
- 93
- Location
- Mesa, Colorado
I was Not getting the low oil psi light. So far I only get that at startup. Rick confirmed the 3126 oil sender is a standalone so no oil light from ECU. I guess that other oil switch could light up the dash but isn't that for the K11 drop out? Transducer is a 1wire not a 3 wire. I need to simply plumb in the new style transducer which has the smaller thread. Yet another $0.95 fitting. Mine had a broken wire lug on it which I had to solder back to the ground. Looks old.
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