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Old 09-14-2010, 03:49 PM   #1 (permalink)
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chevy 6.0 no oil pressure at start-up

got a 2004 chevy 2500HD 6.0L gasser.... 86,000 miles... has been running great up until a week ago..... cranked it up and the oil pressure stayed at zero. revved it up (pretty good) and the pressure came up to normal and stayed good for the 140 mile trip.....since then, when i crank it, i gotta rev it to get the pressure up. it usually only happens when it sits for a while.... if i drive it for a while, then say go in a store and come back out, crank it and it's fine..... but after sitting all night or all day at work it does it....

i hooked up a mechanical gauge last weekend to rule out the gauge cluster or pressure sending unit..... only other thing i can think of is the pump.....

oil has been changed since this started also no difference.

what do you guys think?? anybody ever run into this??
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Old 09-14-2010, 03:51 PM   #2 (permalink)
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sounds like the sump line is draining back into the pan, normal, but if its gotta leak, itll drain...
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Old 09-14-2010, 04:03 PM   #3 (permalink)
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you think maybe the sump line has a hole or something and is draining all the oil back into the pan and MAYBE the hole is big enough it won't "prime" until the higher RPM's put a greater pressure on it????

i think these motors have issues with an O-ring between the pickup tube and the pump.....
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Old 09-14-2010, 07:41 PM   #4 (permalink)
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these motors are known for having problems with the pressure relief valve sticking in the oil pump but if that was the case i don't think you would get oil pressure back just by reving it up unless it is partially sticking i have heard horror stories of people parking and coming back out later and starting the motor up and bang no oil pressure. Also there is a o-ring on the pickup tube where it goes into the pump i had a problem with this if the o-ring is damaged it will have a hard time sucking oil out of the pan at idle but will gain it back at higher rpms but still is not enough to run properly
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Old 09-15-2010, 04:25 AM   #5 (permalink)
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i'm kinda hoping it's just the pickup tube or o-ring..... if i start it and let it idle, it wont build pressure..... rev it and it does.....
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Old 09-15-2010, 05:40 AM   #6 (permalink)
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based on what you've said, i would say pump. more accurately, the pressure bypass on the pump. you can order a ported and shimmed pump from alot of shops, or just buy an ls6 pump for an 03 z06, open in up, port it with a die grinder (once you open it up its easy to see where you need it) and shim the regulator spring with a small bolt. (works better then washers in my experience). have all of $130 in the repair if you have any parts hookups at deallers
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Old 09-15-2010, 06:17 AM   #7 (permalink)
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i can get a melling oil pump for $110..... it's the small stuff thats gonna get pricey..... $50 oil pan gasket, new synthetic oil, etc....
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Old 09-15-2010, 06:55 AM   #8 (permalink)
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Quote:
Originally Posted by jeepin1995 View Post
i can get a melling oil pump for $110..... it's the small stuff thats gonna get pricey..... $50 oil pan gasket, new synthetic oil, etc....
if the oil was just changed then i would just filter it and put it back in, unless you get other fluids in it during the draining process
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Old 09-15-2010, 06:55 AM   #9 (permalink)
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you don't need all that, all you really need is a pick-up oring, crank seal, crank bolt, and water pump gaskets. you can get the pump out without dropping the pan, and even if you do, the gasket can be reused.
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Old 09-15-2010, 08:18 AM   #10 (permalink)
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you don't need all that, all you really need is a pick-up oring, crank seal, crank bolt, and water pump gaskets. you can get the pump out without dropping the pan, and even if you do, the gasket can be reused.
i may have missed it..... you saying if that is my issue i can fix it without replacing the pump?? how? does what your saying do hold the pressure bypass deal open?

it would be nice to not have to remove the oil pan..... heard i gotta remove the front diff to do that....

and thanks for all the help guys i'm new to this truck/motor, but not wrenching.....

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Old 09-15-2010, 08:45 AM   #11 (permalink)
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i may have missed it..... you saying if that is my issue i can fix it without replacing the pump?? how? does what your saying do hold the pressure bypass deal open?

it would be nice to not have to remove the oil pan..... heard i gotta remove the front diff to do that....

and thanks for all the help guys i'm new to this truck/motor, but not wrenching.....
no, you do need to replace the pump, but its driven off the crank snout. there is a 10mm bolt that comes in the bottom of the pump that hold the pickup tube in, then just undo the bolts holding the pump on. it is a bitch to get that 10mm out, but it does come out. if you don't feel comfortable with it, you can loosen the pan bolts and drop it down alittle bit to give you more room. also, if it has any slack at all in it, now is the time to change the timing chain. there are better aftermarket chains available, but bang for the buck its hard to beat an ls2 chain. just order one for an 05 vette. if you plan on using the melling pump, either stick with a single roller chain or be prepaired to do alot of grinding on the front cover. the melling is thicker then the stock pump
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Old 09-15-2010, 08:49 AM   #12 (permalink)
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Exactly. As long as the o-ring style gaskets are still plyable, you don't have to replace them. LS motors are the shiz!!

But like others said, o rings on the pickup are a problem for leaks. If they leak, oil will drain back or not even pick up. But if you gotta pull the diff to get the pan out, I'd replace everything at once - pump and o rings. I doubt it's the pump, though...

I've got a new (on the truck fro under 5k miles) truck pan with a good gasket I'd sell for $20 and shipping. I'll also include new o rings for the pickup tube, as they come in packages and you only need one? to replace the pickup tube. So call it like $40 to your door...Comes with pan bolts, pickup and anything else I can find from the swap
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Old 09-15-2010, 09:05 AM   #13 (permalink)
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he shouldn't have to pull the pan, but if he does, its alot easier to undo the motor mounts and jack the motor off the crossmember
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Old 09-15-2010, 09:07 AM   #14 (permalink)
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he shouldn't have to pull the pan, but if he does, its alot easier to undo the motor mounts and jack the motor off the crossmember
...I'm talking about to replace the o rings, which are probably the reason for his problem. Or are you saying to replace the o ring on the pickup tube that he can do that through the front of the motor too?
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Old 09-15-2010, 09:34 AM   #15 (permalink)
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yes, it can all be done at the pump, which is on the crank snout. water pump, crank pulley, and front cover are all that need to come off
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Old 09-15-2010, 10:50 AM   #16 (permalink)
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appreciate the offer on the pan, but this is going down friday AM..... i'm gonna go ahead and replace the oil pump while i have it pulled apart.....that way theres no question. only wanna do it once..... i really appreciate the help guys. let you know how it goes!


any tips or tricks to make it easier to get to/do?? maybe remove the radiator??

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Old 09-15-2010, 11:37 AM   #17 (permalink)
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You shouldn't have to remove the radiator unless you're swapping the cam out too. Remove the fan shroud, fan, belts, and wp. Remove the crank pulley bolt with an impact, then thread it back in a few turns. Grab the pulley with a 3 jaw puller and use the crank bolt to center it on (protects crank threads). Remove pulley, then start taking out the 10mm bolts holding the front cover on.

Before removing the timing set, reinstall the crank bolt and rotate the engine til the cam gear dot is directly on top of the crank gear dot (this isn't required if you aren't going to change the timing set).

On the bottom passenger side of the oil pump you will see the pickup tube installed, being held in place by a 10mm bolt. There is next to no room there, but it does come out without having to drop the pan. You may need to remove the bolts holding the pump on the front of the block to move an manipulate the pump in order to get the pickup off. Once it is removed, the pump slides off the crank gear.

Pour a little oil into the pickup of the new pump before you install it. Not to the point it runs out everywhere, just enough to coat the the gear inside. This helps with the priming on startup. Slide the new pump on the crank gear, then reinsert the pickup tube with a new o-ring on it. Be carfeful when installing it because it is very easy to cut or nick the o-ring on the pump body. Also make sure it is installed all the way in the pump before tightening down the pickup bolt, as it can slide down and get pinched during installation. Line up the pump with the bolt holes, and reinstall everything.

Drive out the old crank seal in the front cover and install a new one. As long as the rubber hasn't separated from the aluminum on the cover gasket, it can be reused. Put a dab of RTV on both corners on the oil pan where the front cover sits and loosely reinstall the cover. Do not tighten down the bolts yet.

Reinstall the crank pulley. The stock bolt isn't long enough to be threaded in when you side the pulley on, so you either have to buy one at the hardware store or tap the pulley on far enough to get a few threads of the bolt started. make sure you have good engagement, or you'll strip the crank out when you run in the bolt. I always run the pulley in with the old bolt, then remove it and hammer down on the new one. It has to be replaced as they are one time use torque to yield bolts (they stretch).

Now you can tighten up the cover bolts. Doing this before the crank pulley can lead to front seal leaks.

Reinstall water pump (Check the gaskets, replace if needed), belts, hoses, ect. Fill with coolant. Unplug the coil packs on both sides and turn the motor over. The oil pressure should start to rise. Plug the coil packs back in and fire it off.

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Old 09-15-2010, 01:12 PM   #18 (permalink)
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wow..... thanks a bunch!!!

sounds pretty straight forward. done axle swaps and motor swaps..... this should be easy..... just time consuming!!
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Old 09-16-2010, 11:47 AM   #19 (permalink)
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I would replace the timing chain as well, while you in there. If you notice it has a lot of play. These usually only last 100k miles then they start getting sloppy.
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Old 09-16-2010, 01:21 PM   #20 (permalink)
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I would replace the timing chain as well, while you in there. If you notice it has a lot of play. These usually only last 100k miles then they start getting sloppy.
Agreed... At this point you are already there anyway.
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Old 09-17-2010, 05:59 PM   #21 (permalink)
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DONE!!! wow that was a job!! was able to do it without dropping the oil pan.... new oil pump, timing gear, t-stat and gaskets.... waterpump looked almost new and was tight. problem is fixed. appreciate the help and tips guys.

beer time.....

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Old 09-17-2010, 08:06 PM   #22 (permalink)
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Did you see anything that would be causing your problem? Or did you just toss all new parts at it and not inspect what you took off?
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Old 09-18-2010, 04:50 AM   #23 (permalink)
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only thing i noticed was when i reinstalled the pick-up tube, it fit a little tighter than before i replaced toe o-ring.....
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