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Oil pump oddity

ak diesel driver

ak diesel driver

6.5 driver
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Location
alaska
So my buddy recently refreshed his 6.5 and we noticed something odd. They show a standard volume pump without a spacer and then a standard volume pump with a spacer and finally a high volume pump which also has a spacer. Turns out the gears on both pumps with spacer are the same and only the one without the spacer has shorter gears. So your paying $10-20 more for the same pump, or so it seems. https://www.rockauto.com/en/catalog...sel+turbocharged,1053391,engine,oil+pump,5564.
All the flaps are the same. Anyone have any thoughts on this?
 
ak diesel driver said:
So my buddy recently refreshed his 6.5 and we noticed something odd. They show a standard volume pump without a spacer and then a standard volume pump with a spacer and finally a high volume pump which also has a spacer. Turns out the gears on both pumps with spacer are the same and only the one without the spacer has shorter gears. So your paying $10-20 more for the same pump, or so it seems. https://www.rockauto.com/en/catalog...sel+turbocharged,1053391,engine,oil+pump,5564.
All the flaps are the same. Anyone have any thoughts on this?
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I wonder if the oil pickup screen tube is a little shorter to accommodate the added depth of the portion of the pump that mounts to the block ?
If that is not different then the oil pump drive shaft would need to be shorter.
Something gotta give someplace. 🤷‍♂️😹
 
Funny this comes up today, I just got a message back from melling today, the difference is in the relief spring, the 255HV294S has a different relief spring than the other , yes there is 3 different pumps. I'm not positive but I know the p400 has a different part number for the oil pump because it has more oil passages in the girdle, I can only guess it uses the above number pump. Melling stated it has a 80lb relief spring.
 
Quoting myself because it’s fun. Keep in mind it was June of 2014 when I wrote this.
There might just be a different manufacturer by now. Find the brand, get the specs from them. Then call Melling.
Will L. said:
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.
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ak diesel driver said:
So it turns out he actually had 2 without the hv in the number, he ordered the hv.
Chris what should a new engine run for oil pressure at hot idle?
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It somewhat depends on bearing clearances, I stay as close to .0020-.0025 as I can . Oil psi should be around 60-80 at idle.
 
I have a couple of questions from reading through this thread.

1. Out of curiosity with a worn engine showing about 20 psi at hot idle and would increase to around 40 under load. how far gone would one say the cam bearings are?

2. How hard are they to replace without or can they be replaced without pulling the crank and pistons? I would assume the engine would have to be pulled and flipped upside down to replace them.

3. replacing the oil pump with a HV would only gain at most 5% pressure back. so I would assume if I wanted to go that route in the future (that is if I pull the engine to replace leaking gaskets and seals) I would maybe see 1 psi greater with a new HV pump? or would this be the better route to go if I wanted to prolong or extend the time before death of a worn engine not worthy of a rebuild?
 
dbrannon79 said:
I have a couple of questions from reading through this thread.

1. Out of curiosity with a worn engine showing about 20 psi at hot idle and would increase to around 40 under load. how far gone would one say the cam bearings are?

2. How hard are they to replace without or can they be replaced without pulling the crank and pistons? I would assume the engine would have to be pulled and flipped upside down to replace them.

3. replacing the oil pump with a HV would only gain at most 5% pressure back. so I would assume if I wanted to go that route in the future (that is if I pull the engine to replace leaking gaskets and seals) I would maybe see 1 psi greater with a new HV pump? or would this be the better route to go if I wanted to prolong or extend the time before death of a worn engine not worthy of a rebuild?
Click to expand...
Your pressure is ok for a used motor, your bearings are loose but not gone yet. It wouldn't make much sense to only change some bearings.
 
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