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What did you do with your GMT400 today...or yesterday....

Been away for a while folks, but now I’ve got a question.

On my 6.5, how do I check the ACTUAL oil pressure? I have no idea if my dash gauge is feeding me BS or if the oil pressure really is fluctuating wildly...
I fear damage may already have been done if the pressure is actually bad as it sat idling for a while before I saw what it was doing 😬
 
All the bolts, nuts, studs and whatnots is moved off the truck. Bed is cleaned out. Parts stowed. Ready to pull this unit from its warm secure place out into the cold, and hope no snow, at least if it does snow, let the truck get down to the air temp first. Then the snow can be gone with a puff from the leaf blower. 😹😹😹
 
J_dude said:
Been away for a while folks, but now I’ve got a question.

On my 6.5, how do I check the ACTUAL oil pressure? I have no idea if my dash gauge is feeding me BS or if the oil pressure really is fluctuating wildly...
I fear damage may already have been done if the pressure is actually bad as it sat idling for a while before I saw what it was doing 😬
Click to expand...
Only sure way is with a mechanical oil pressure gauge.
Unless the remote hose has been installed, the intake has to come off to get to the port. Where the sender unit is screwed into the block.
If You have the intake manifold off, probably want to replace the fuel hoses from the FFM to the injection pump, and, from where the fuel hoses hooks to the FFM back to the supply/return pipes behind the bell housing.
And as has been suggested by several members of the forum, use only SAE 30R9 rated hose to withstand diesel fuel.
 
J_dude said:
Been away for a while folks, but now I’ve got a question.

On my 6.5, how do I check the ACTUAL oil pressure? I have no idea if my dash gauge is feeding me BS or if the oil pressure really is fluctuating wildly...
I fear damage may already have been done if the pressure is actually bad as it sat idling for a while before I saw what it was doing 😬
Click to expand...
While at the NAPA store I got a hydraulic hose made, 1/4” X about 30 inches. 1/4” female on one end and 1/4” male on the other end. I screwed a brass street L into the block where the OP sensor screws into. Aimed the L back and gowards the RH side of the valley. I now have the OP sensor screwed into that extension hose.
Now if the sender ever goes bad or starts to leak, I’ll be able to get right to it.
I did check the hydraulic hose with the ohms meter. It does get continuity from the oil pressure sensor to the battery negative post. Hydraulic hose is steel braided within the rubber sheathing.
Also, NAPA did not have some 30R9 hose, at this store. They do have a red hose thats compatible with oil, fuel and withstands a lot of heat. So thats what I chose to use.
 
MrMarty51 said:
Only sure way is with a mechanical oil pressure gauge.
Unless the remote hose has been installed, the intake has to come off to get to the port. Where the sender unit is screwed into the block.
If You have the intake manifold off, probably want to replace the fuel hoses from the FFM to the injection pump, and, from where the fuel hoses hooks to the FFM back to the supply/return pipes behind the bell housing.
And as has been suggested by several members of the forum, use only SAE 30R9 rated hose to withstand diesel fuel.
Click to expand...
Oh dang, that’s not great. There’s no other port to check pressure from?! What was GM thinking?!
 
Hmm somebody on DieselPlace or somewhere mentioned a port I could tap into down by the oil filter, anyone here know about this? I’d really prefer to verify oil pressure before tearing things apart in the middle of the yard in a snowstorm...
 
J_dude said:
Hmm somebody on DieselPlace or somewhere mentioned a port I could tap into down by the oil filter, anyone here know about this? I’d really prefer to verify oil pressure before tearing things apart in the middle of the yard in a snowstorm...
Click to expand...
The easiest way is through the OP sensor port behind the intake on the drivers side. just pull the sensor and thread a hose with 1/8" npt into the port with a gauge on the other end. it will run and idle without the ops installed for a few minutes. just don't drive it because without the OPS, your lift pump will not be working.
 
MrMarty51 said:
I seen those and just think they’d be a nice option.
No money for that today. Barely getting done what I got to in order to get it back together.
Only reason I took it down was because of the cold engine misfire, knew at least one injector was messing up. Didnt realize it was the whole engines worth. Did not want to travel it any farther than necessary for fear of torching a piston or two.
Now I guess I understand why the fuel mileage dropped off to 15-16 at 72 or 73 MPH.
Had to keep it at about 60 to 65 to maintain that 18 MPG.
Click to expand...

I wish I could get past the 15-16 mpg's I'm gonna wait patiently to see your outcome on better mileage once you get your new injectors installed.
🍿 🍿
 
dbrannon79 said:
The easiest way is through the OP sensor port behind the intake on the drivers side. just pull the sensor and thread a hose with 1/8" npt into the port with a gauge on the other end. it will run and idle without the ops installed for a few minutes. just don't drive it because without the OPS, your lift pump will not be working.
Click to expand...
Ok sounds simple right?
I see nothing easy about that method but ok 😂
I don’t have the “special tool” for that sensor, would a regular crows foot wrench work? Not that I have one of those either 😆
 
MrMarty51 said:
Only sure way is with a mechanical oil pressure gauge.
Unless the remote hose has been installed, the intake has to come off to get to the port. Where the sender unit is screwed into the block.
If You have the intake manifold off, probably want to replace the fuel hoses from the FFM to the injection pump, and, from where the fuel hoses hooks to the FFM back to the supply/return pipes behind the bell housing.
And as has been suggested by several members of the forum, use only SAE 30R9 rated hose to withstand diesel fuel.
Click to expand...
There's also ports by the engine oil filter.
 
Yeah, I forgot about that special socket. I have gotten mine off with a pair of channel locks in the past, plus I don't have the FFM sitting there taking up all the room. I forgot that it's a PIA to get at with the FFM in place. I'm not sure exactly which port is for the oil pressure up by the filter. I will have to look at the block I have on the stand tonight after work. maybe others might have a pic or two showing that port and how hard it is to get to with the engine in the truck.
 
Moved the truck from the garage. Snowing like crazeeeee out there. The step son backed his truck in, we unbolted the ladder rack and slid it off to make welding on it easier.
He came from being a pipeline welder to owning his own electrical contract company.
FB5AD22C-65DA-42AA-B4C4-5593BD81553D.jpeg
 
Yeah it’s kinda tight by the fuel filter, I shoulda relocated that years ago. There’s also too much grime by the oil filter to see any other ports in that location. Oh well I think I can cobble something together to get at the OPS with an old socket, possibilities are endless when you have a welder 👍🏼😁
 
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