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09 Silverado 5.3 LC9
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Discussion Starter · #1 ·
Hey guys I’ve looked through and can’t seem to find anything new to check on my truck. I should mention this is my first ls rebuild, so I think I checked most of the common issues with low oil pressure after rebuild, new sending unit and no screen under it, barbell in place Oring on pickup tube new and in place. I went with summit oil pump and actually had them send me a replacement one I thought may have been bad(sum-121170) but same problem cold start gauge goes to 22 psi and as it warms the pressure drops to the point it comes into alarm. I have not put a mechanical gauge on it, but I have pulled valve cover off and started it even on cold start no oil to rockers. Trying not to have to pull it out of truck and tear back down is there anything else that could b restricting pressure? One last thing I will mention not sure if it’s relevant but the first couple starts my gauge was pegged out at 80 then after that it was at zero until I replaced sensor figured that was a sensor malfunction but thought I would mention it thanks in advance for any help
 

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^^^^ this. I guess the first thing I'd do is put a mechanical gauge on it to verify the pressure.
 
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This may be a dumb question, but what weight oil did you put in it? It's been a while since I checked, but I think the clearances between crank/cam and their bearing surfaces should be something between 0.001-0.003".
 

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I went with summit oil pump and actually had them send me a replacement one I thought may have been bad(sum-121170) but same problem cold start gauge goes to 22 psi and as it warms the pressure drops to the point it comes into alarm.
You put the wrong oil pump in your truck. M365 is the correct pump, it pumps 1/3 more volume per revolution than the M295 you chose. The M365 is made for aluminum engines with our greater tolerances compared with the iron block motors and it pumps at lower pressures which is just fine.
 

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09 Silverado 5.3 LC9
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Discussion Starter · #6 ·
I’m not sure on my clearance at crank and cam I didn’t realize that was so vital to oil pressure sounds like I will have to pull it to get those measurements and see what tolerance is
 

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Discussion Starter · #7 ·
I’ll try to answer all ur questions in one resonance I used Mobil 1 full synthetic 5w-30 and Mobil 1 filter,
All bearings were replaced, I can try to pick up a mechanical gauge to try but the only places I can install it are front drivers side of block and oil pressure switch on back top of motor, and is the m365 you mentioned still going to run lower pressure
 

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You could try shimming your oil pump and pan relief valve...


 

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09 Silverado 5.3 LC9
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Discussion Starter · #9 ·
I haven’t tried shimming the pump yet I do still have the old one I took out I am thinking bout putting back in I’m not sure what part number it is but it can with my dod delete kit from btr and I have already put a plug in the pan relief valve
 

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...and is the m365 you mentioned still going to run lower pressure
The bypass is set for 36-38 psi. It run around 40 psi when cold and once it heats up the pressure will be in the upper 20s in gear at idle. You don't need more pressure since you have so much more volume. Put the right pump on the motor and then see, where's your original one?
 

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I did a delete kit from btr bout year ago so it’s long gone but I have the one I got from them. I added a pic of the pump I got from them View attachment 944590
Ain't the right one either. M365/12612289/12710304 is the one for your engine. Melling is best. The gerotor is at least 1/3 larger than the iron block pump's.

Plug your VIN in here:

If interested in learning more, google "Rebuilding GM's Gen IV engine". Won't let me upload it here as a pdf.

You guys can't trust these kit sellers, even the big name ones. They sell you smaller camshafts than stock and the wrong oil pumps and some of them are using Chicom lifter trays instead of GM OE and customers are losing motors and performance.
 

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Discussion Starter · #13 ·
Ain't the right one either. M365/12612289/12710304 is the one for your engine. Melling is best. The gerotor is at least 1/3 larger than the iron block pump's.

Plug your VIN in here:

If interested in learning more, google "Rebuilding GM's Gen IV engine". Won't let me upload it here as a pdf.

You guys can't trust these kit sellers, even the big name ones. They sell you smaller camshafts than stock and the wrong oil pumps and some of them are using Chicom lifter trays instead of GM OE and customers are losing motors and performance.
Ok I’ll see if I can find one local tomorrow if not I’ll have to order one thanks
 

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Discussion Starter · #14 ·
Question before I go buy a m365 pump I get what your saying bout the pump being wrong but my question is even if these other pumps are wrong wouldn’t they still atleast hold pressure I did some more looking on sites last night and looking at melings site they say the 355 I have is supposed to work for my motor so I figured before I buy new I would try it installed it this morning and while it did take longer to bottom out the gauge it still ended up not holding pressure at idle for more then like 3 mins and I have rockers rattling
 

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Question before I go buy a m365 pump I get what your saying bout the pump being wrong but my question is even if these other pumps are wrong wouldn’t they still atleast hold pressure I did some more looking on sites last night and looking at melings site they say the 355 I have is supposed to work for my motor so I figured before I buy new I would try it installed it this morning and while it did take longer to bottom out the gauge it still ended up not holding pressure at idle for more then like 3 mins and I have rockers rattling
I do not know for sure. I just saw the wrong pump on there and pointed it out. The gerotor on the 355 is way smaller than the 365. When you put the motor back together, did you check all the clearances with plasti-gauge, especially the camshaft journals?
 

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Discussion Starter · #16 ·
I do not know for sure. I just saw the wrong pump on there and pointed it out. The gerotor on the 355 is way smaller than the 365. When you put the motor back together, did you check all the clearances with plasti-gauge, especially the camshaft journals?
No I didn’t I went off machine shop numbers they gave took ten out of rods and mains and I put new cam bearings in
 

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Discussion Starter · #17 ·
Ok so update time, after reading all the comments made me think about going through my order from summit. And they sent me standard main bearings instead of 10 over so after an hour on the phone with them I got them to send new bearings and m365 pump. Installed and started last night now I’m a lil concerned it may be to high of pressure first start went right to 60 psi and after it warmed up a lil dropped to roughly just under 50psi but taking idle up to around 2-2500 it gets up to like 70psi debating on if I should put relief valve back in to the pan or possibly look at shimming pump relief. Opinions
 

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How long did you let it run? Did you let it fully warm-up?

Won't shimming the pump relief make pressure go higher?
 

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Discussion Starter · #19 ·
I did let it get up to operating temp ran bout 5 min or so. And I’m not sure on shimming thats why I’m asking I feel like the pressure is a lil high myself but at same time I don’t want it to run like 20-25 psi either. When I got my truck it ran 40psi constantly so that’s where I would like to see it run jus not sure what combination I have run to get that. Thanks
 

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I did let it get up to operating temp ran bout 5 min or so. And I’m not sure on shimming thats why I’m asking I feel like the pressure is a lil high myself but at same time I don’t want it to run like 20-25 psi either. When I got my truck it ran 40psi constantly so that’s where I would like to see it run jus not sure what combination I have run to get that. Thanks
Normal hot idle in gear oil pressure is in the 20s, the bypass spring is set for 36-38 psi, can't remember which.
 
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