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Oil pressure low?

matuva

matuva

Tropical 6.5er
Messages
1,996
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Location
New Caledonia. An island in south west pacific, cl
Here is a picture of my oil pressure, idle hot. It then establish at 275 cruising hot, and is around 300 at cold when starting.
Nothing to compare with my previous optimizer which was settling at 275 hot idle and 400~410 cruising hot

Oil pressure idle hot.jpg

The oil pump is a brand new HO SEALED POWER Part # 22443621

Does it sound good or should I look for a better pump?
 
converts to 20-25 psi? sounds low have you checked it with a mechanical guage? did you replace the cam bearings?
 
I saw sellers selling High Volume pump, or high pressure pump? I don't understand: If you get high volume, that also means high pressure? The more volume you put in an oil passage, the more presuure you get? So, what's the difference?

Spring color also means something?
 
High volume will put out more volume but the pressure relief is still set at stock PSI. High pressure will have a higher pressure relief setting. 97+ pumps are high volume to make up for the piston cooling oil squirters. never seen a high pressure pump for a 6.5
 
About a year and a half ago I started this chase for the best oil pump and different options and willing to spend $500 range.

Melling is the only manufacture of the 6.5 oil pump-end of story. They make them and every company out there has a Melling relabeled to their own name.

There is the low volume pump. There is the taller gears,spacer and longer cap bolts to work with it to make it a high volume pump. There is one optional spring that is for the relief in the pump to maintain higher pressure in the pump body before the gear passage, but will of coarse lower the volume some. 3 options, no more.

The Melling engineer I spoke to in quite detail explained it like this: The volume difference between the 2 springs will have less effect than the ambient operating temperature you are in if your morning starts out at 50 degrees morning and gets to 85 degrees in the afternoon. (F not C - sorry Matuva). The clearances of your bearings determine your pressure far more than anything else. A worn out pump with proper cam, main and rod bearing clearances will have higher pressure than a new pump with the tighter spring if your bearing clearances are of by 3%. He did say not to panic much because the testing they showed with the 6.2 and non squirter 6.5 that 8 psi was ample and squirter 6.5 that 9 psi was ample.
As long as that pressure is maintained that means the flow is good enough to keep everything lubed and still float the rotating component at load.
Melling did a buy back program of engines after 150,000 miles and re-tests for real world analysis back in the day and the 6.5 turbo was one of the samples. They got 100 trucks,flushed the oil system recorded pressures. Then replaced the oil pump with new pumps and retested. Only a 4-5% gain, % not psi. They took 2 engines did cam bearings only,2 main only, 2 rod only, and 2 all bearings. The cam bearings are the issue. Doing the lowers barely helped, but the cam bearings were responsible for 75% of pressure loss.

The engineer I spoke to by the way that explained all this and did the testing is the one that when I read him the list of brands selling oil pumps sent me the snapshot of each of the boxes and labels. They box and label them there -shipped ready to sell. I found most the different companies selling the pumps, he laughed and said I missed one but wasn't allowed to tell me who it was, but can verify if you ask them -do you make the pump for "x"? The phone he texted the pics to went swimming in Lake Mead, so I can't share the mfr plant snap shots, sorry.

In the end get a new high volume pump at the best price you can, because it will be the same pump anyways. If you order the one with the spring kit option you can play with it like I did, but don't expect noticeable differences all my bearings were new and plastigauged mighty nice. If you cam bearings have 40,000 miles on them you will not see a difference in the springs.
 
Thanks for these informations Will ;)

At least I know the engine is lubed enough, despite this low pressure.

There's a good chance the engine will go out (one more time, I know) as my mechanic prefers pulling the engine to work on oil pan leak and possible craked head.

I will take the opportunity to check the mains and rod bearings. I know he torqued these bearings below torque specs, and the explanation of low pressure may sit there...
 
If it has squirters, 15-20 at a hot idle is fine. I've seen stock trucks with the squirters in it hold 10-15 PSI on almost new engines, but they will jump up to 40-50 at 2000 RPM's. And run a high volume standard pressure pump. Pressure isn't important, volume IS important. The oil volume is what you need, not pressure. Anything more than about 50 PSI is just wasted HP as it takes power to run the oil pump.
 
I have lost a couple ticks on oil pressure when I turn on the headlights. A better ground strap from the body to the engine helped the gauge continue work properly when the headlights turn on.
If you don't have a ground strap or haven't checked grounds - esp after major work could have broken them... Now is a good time.
 
Yes Melling. Yes your fine.

WW- are you trying to tell me GM went shy on the grounds for something? idk if I believe that...
 
Will L. said:
Yes Melling. Yes your fine.

WW- are you trying to tell me GM went shy on the grounds for something? idk if I believe that...
Click to expand...

:bigeyes: I didn't believe it either but: I seen it with my own eyes I swear! But I may be more than just color blind.

Looking at the OP's pic closely - I see that the oil pressure is the top gauge - out of habit my 1995 was the bottom left gauge and extreme left on the 1993... Anyway this appears to be normal oil pressure when hot. The temp gauge I was looking at is low for oil pressure. :34: Anything over the 1/4 mark is normal to me on GM diesels.

Engine getting up to operating temp? The temperature gauge looks on the cold side.

You should check your oil for a fuel smell as this could cause pressure loss. The suggestion from Bison in the #2 leak tread made me think of this assuming it's the same engine.
 
yup, same engine with 3 different threads for different problems :rolleyes5:

Injectors are brand new Bosch, which were used on my former Ted's engine. This pressure is the same since the first start, and oil doesn't smell fuel.

This engine runs very smooth, not a tick or a knock, smooth as silk...
 
matuva said:
yup, same engine with 3 different threads for different problems :rolleyes5:

Injectors are brand new Bosch, which were used on my former Ted's engine. This pressure is the same since the first start, and oil doesn't smell fuel.

This engine runs very smooth, not a tick or a knock, smooth as silk...
Click to expand...
I don't say it is but you could have an injector that has poor atomization at idle but working fine with higher RPM's.

Older John Deere, Belarus and the GM two stroke diesels are notorious for having black soothy diesel running down the exhaust stack with prolonged idle, it is the nature of the beasts.
 
WarWagon said:
I have lost a couple ticks on oil pressure when I turn on the headlights. A better ground strap from the body to the engine helped the gauge continue work properly when the headlights turn on.
If you don't have a ground strap or haven't checked grounds - esp after major work could have broken them... Now is a good time.
Click to expand...

Having all the normal grounds, cleaned and tight. I have found that the ground path internal to the instrument cluster is a little flaky. The ground to the cluster was good, but inside the trace foil had resistance.

I had added a ground wire from dash frame to one of the cluster lamps, raw wire under the twist lamp holder. The flaky gauge readings and fluctuations when the turn signals are on went away.
 
jmiller said:
Having all the normal grounds, cleaned and tight. I have found that the ground path internal to the instrument cluster is a little flaky. The ground to the cluster was good, but inside the trace foil had resistance.

I had added a ground wire from dash frame to one of the cluster lamps, raw wire under the twist lamp holder. The flaky gauge readings and fluctuations when the turn signals are on went away.
Click to expand...

I got to try that out.

I assume the OP did not use exhaust manifold gaskets. Over some short time the manifolds will seal themselves with soot. Maybe just not enough time for them to seal with soot yet.
 
The only thing you have to do with any Oil pump is to put red locktite or drill and safety wire the bolts of the pump and torque them to 80 inch pounds, I have seen them loosen and the cover drop enough to lose OP and destroy an Engine, They are often not tight from the factory
 
Gotta run so didn't read the thread, but check the oil pressure switch (OPS) if that hasn't been mentioned yet. Mine ran like crap until I found mine falling apart- now I keep a spare in the truck. They apparently fail more than we'd think. About $50-60 at the dealer, easy to replace near the upper fuel filter.
 
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