Low oil pressure on rebuit 6.5

[4x4 Nut]

Hello. I have an oil pressure issue I can't seem to figure out. I've recently rebuilt a '96 6.5L that was in sad shape mechanically. It was bored .030 with new pistons/ rings, new heads, good polished crank with stock grind, cam checked out fine and new bearings installed. The block was magnafluxed and all the bearings and gaskets were replaced along with a new oil pump. The cooler was flushed out. The engine has Rotella 15W40 in it with a Hastings filter. The machining was done by a very reputable shop in our area. While putting it together we plastigauged a few of the bearings and found all was good. The turbo has a good feel to it with no movement and free spinning. I know the oil plugs in the block beside the cam are installed. That should cover the history on it.

We primed the pump and fired it up. We had about 40- 45 pounds immediately and it ran good. As the engine warmed up (about 15 minutes run time) the pressure kept dropping off to around 10 PSI while the temps were up around normal operating range. I installed a mechanical gauge connected to a T in the turbo supply line and restarted it. The mechanical gauge showed 8 PSI at idle warmed up. We started looking at possiblities and found that the 2 bypass valves above the filter were removed at the machine shop and neither of us had reinstalled them. New ones were ordered and we installed them along with the correct frost plug. I thought for sure it would be taken care of, but instead our cold oil pressure dropped some to about 30 PSI and we're still dropping off to 8# warm at idle. It will come up when the engine speed is increased, but only to about 30-35 PSI.

I have not driven the truck yet so the oil has not been hot even during our checks. I am wondering if we don't have a faulty oil pump and am about ready to pull the pan to try it, but am not looking forward to that.

Would anyone have any suggestions or thoughts in figuring this out. Thanks in advance. It is greatly appreciated.

[john8662]

More plugs to check...

Did the machine shop remove the plug that is up in the block that separates the filtered from the unfiltered oil? This plug is up above in a hole under the rear main bearing cap. Small block gassers have a plug in this area too, and some machinists remove it. Perhaps it's not there...

Also, the two front plugs at the front of the block right behind the cam gear (or a little above), they can be forced out or forgotten...

Really, every journal should be plasti-gauged, all the mains and at least one rod of the pair on each throw, that way you know.

J

[Kennedy]

definitely ask them about the hidden plug. This plug is removed in order to facilitate proper cleaning and primarily removal of cleaning debris. If they forgot the filter and cooler bypass valves I'm sure they didn't get this one either.

If the rods were resized and the crank mic'd you should be good provided the line bore was good and this would show in turning the crank by hand. Plati gage isn't really used much these days.

[arveetek]

More plugs to check...

Also, the two front plugs at the front of the block right behind the cam gear (or a little above), they can be forced out or forgotten...

J

Yeah, those two plugs right behind the cam gear are easy to forget! However, you probably won't have any oil pressure at all from the oil dumping right back into the pan, and the lifters won't pump up and the engine will run like crud!

Don't ask me how I know!! :rolleyes:

Casey

[DennisG01]

For what it's worth, take a look at this thread, it might (or might not!) help: http://www.thedieselpageforums.com/tdpforum/showthread.php?t=31175&highlight=oil

I have a bright red light on my dash that goes on whenever (if) the oil pressure falls too low. The pressure switch is T'd into the top of my turbo. The switch I ended up using is rated at 8-12 psi. Anything higher than that and the red light would come on when the oil warmed up. My dash gauge still shows higher - maybe 35 or so. Once I get the RPM's up, the dash gauge reads pretty close to what a good mechanical gauge reads at the turbo.

[4x4 Nut]

More plugs to check...

Did the machine shop remove the plug that is up in the block that separates the filtered from the unfiltered oil? This plug is up above in a hole under the rear main bearing cap. Small block gassers have a plug in this area too, and some machinists remove it. Perhaps it's not there...

Also, the two front plugs at the front of the block right behind the cam gear (or a little above), they can be forced out or forgotten...

Really, every journal should be plasti-gauged, all the mains and at least one rod of the pair on each throw, that way you know.

J

Thanks for the reply. I now have the pan off and pulled the rear main cap too. The small plug in the block is in place so I guess that's covered. I know the plugs behind the cam gear are in place and tight. This is a newer block with threaded plugs instead of the frost plugs and we double checked them before going together.

The machine shop had checked the crank and told us both rod and main journals were standard. We double checked a few with plastigauge and found them to be OK, but the crank had been mic'd and polished. The block had been line bored and the rods reconditioned too.

I think I'm going to put the main cap back on along with the oil pump, put some oil to the sump and drive it with a drill to see if I have any large amount of oil dumping from strange places. It'll be messy, but I don't know what else to try.

Thanks for your responses guys.

[john8662]

Which oil pump did you use?

The standard oil pump, or the one for a '97 or later piston oil spray block?

What is the cast number of this block? If it is really a 1996 block it will have a casting number ending in '141.

Otherwise, if it's a '506 you'd better have the High Volume oil pump installed.

Sounds like the plugs are installed, glad you checked the one under the bearing cap. It's a real PITA to change... It's also good that this block has the threaded plugs in the front.

[Robyn]

Another issue could be the squirt nozzles in the main saddles.

If some of these were left out the oil will drool out by the buttload resulting in the loss of pressure.

The holes in the main webs are fairly large and have small squirt nozzles in each hole.

These have been known to get lost during cleaning.

As long as the other items listed above are in place this could very well be the issue.

Best

Robyn

[4x4 Nut]

Well we ran the pump with a drill and found 1 and maybe a 2nd place where a cooling nozzle appears to be missing. It blows about a 1/4- 3/8" stream of oil up underneath the piston, but only with enough force at 15 PSI to barely reach the piston while it's at the bottom of it's stroke.

I've called the GM dealer and the VIN off this '96 truck doesn't show these nozzles used, but checking a '97 or '98 does. It appears that we either have an odd one or the engine has been changed at some point. The parts man also said they show a 6mm and 8mm plug- don't know if it's both or option of the 2. We also have the standard oil pump and a '98 calls for a different part number- high volume I'm sure.

Does anyone have a picture of what these nozzles look like? I'm hoping they are threaded and that we can get them in from underneath.

This truck has been such a pain. I'm sure these nozzles will take care of the problem, but I wish it was done. Thanks a bunch for your help guys. It is much appreciated.

[john8662]

No one ever takes the nozzles out.

Let me know what the cast number on the block is, that will help shed some light on your situation. I'll bet the engine has been changed and is a '506 block, no 1996 141 blocks had sprayers.

The nozzles are little aluminum tits, they are pressed in from the bearing journal. You have to have the crankshaft and bearing half removed in order to install or remove them.

You might want to take a small mirror (telescoping) and look at your suspected nozzle hole. Any of the middle sprayer holes in the block the sprayer nozzle tip will NOT protrude from the bore. So you kinda have to look inside the 1/4" hole to see if the nozzle in in there. If you're getting a 1/4" solid stream of oil, it's very possible it's missing.

Your machinist SHOULD HAVE THESE if he took them out (if not, kick some butt).

Yes, you'll also need the High Volume Oil pump (if your block is indeed a sprayer). Remember, find that cast #, the date code off the rear pass side would be helpfull too (to ID nozzle diameter you need).

[4x4 Nut]

It is a 506 block- #12555506 with date #E039. I ordered both sizes of nozzles from GM and I guess I'll be pulling the engine back out and installing them. I was really hoping they would be threaded like a small pipe plug and that I could install them from the top side of the main webbing, but that's not the case.

I don't think the machine shop removed the nozzles, because they've had to do a lot of research as well and said they've never had this problem before. I am a little disappointed that it wasn't caught though. I wonder if it was missing one from the beginning and this is ultimately the reason the engine went bad. Oh well, it will be right when it leaves and I'll be glad when it's finished up.

[john8662]

Likely the larger nozzle as your block is an early 1999 block (April, 1999).

You for sure need the 1998+ oil pump for that engine, it it noticeably larger than the stanard oil pump.

Is this your own truck or a customers?

If you would when you get the nozzles, compare them via picture and measure their required bore diameter. I've only seen the larger, but would be curious which fit.

[4x4 Nut]

I do have the newer pump as well. I forgot to mention that. It's a customer/ friend's truck. I have both nozzles now and according to GM, there is a 6mm and a 8mm. I'll be finding out which one fits here in the next few days.

Thanks a bunch for all of your help guys.

[4x4 Nut]

Well, we pulled the engine and then the crank. I found that 4 out of the 8 nozzles were missing. It took the smaller 6mm size and after putting it back together, we now have decent oil pressure. It will run 50 PSI cold idle or revved up and 15 PSI at hot idle. I'm very relieved that it's now taken care of and behind us. Thanks to everyone for the help. It's much appreciated.