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Discussion Starter #1
My recently aquired '87 Sub 6.2 runs really well, doesn't smoke at all, and is quiet cold or hot. So why when I'm riding around does the oil pressure appear to drop? I noticed it as low as 5 lbs, and the needle seems to respond to RPM, so I sorta trust it. I thought the oil pickup might be blocked with sludge, so occasionaly I'll turn the engine off for a few seconds, then re-start. All while going down the road at 60 mph. I filled with Rotella syn 10W40, AC Delco filter. Oil was clean after 1000 miles, a sign of frequent maintenance. Odo shows 70k, mabe 170k. Temperature is below freezing, runs 200f. I will change sender, and might install a quality mech guage.

So my question is, does somebody make a HIGH VOLUME oil pump? Melling lists only the standard unit. I would also install the steel shaft.
 

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Eagle Eyes
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try maybe a new oil pressure sender. they always act funky
 

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Also check the wiring - I've got a bad wire to the sending unit in my harness, so time to pull new wires.
 

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What kind of pressure do you see under these situations:

Cold initial start (idle)?
Cold Driving (~1500+ RPM) ?

Hot idle PSI
Hot Driving PSI (~2000 RPM, highway speed)?

To answer the question about a Higher Volume pump, yes there is one available.

The 98+ 6.5TD engines had a larger Higher volume oil pump that is a factory unit, it is physically larger in size and has a higher capacity, not PSI. Melling makes the equivalent part (to the GM), you will need to buy the matching oil screen pickup/tube. The rest is bolt in, same block design (basically).

Your best bet is to pickup a mechanical gauge to temporarily install. Unscrew the the factory sender and install the tubing kit in the place of where the sender was for your mechanical gauge. You might run the tube in the cab to see the gauge, or just leave the gauge under the hood for reference to diagnose a truely low PSI situation.

If you do have lower PSI readings that what you expected, then a good flush is in order. Get the engine up to normal operating temp. Then drain one qt of oil out of the crankcase (right before an oil change of course), then add one qt of raw diesel fuel to the oil. Start the engine and let it idle for 10 minutes without reving it up, then shut down the engine, drain oil and replace, fill with fresh oil. I have noticed a BIG difference on my '82 that had low HOT oil pressure, I gained 10psi afterwards.
 

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Before you get too deep into changing the oil pump (or anything drastic, for that matter), do like chevydiesel said and get a mechanical gauge. They are much more accurate than any electrical gauge could ever be.
 

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Eagle Eyes
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oil pressure seems to change with what type of oil you are using. a 15w40 setup will typically show less pressure then a HD30 setup will.

I dont do alot of 1500+RPMs because of overdrive tranny, but im running 15w40 at the moment and see close to 80psi on startup and 40-45psi when hot. for HD30 I think I saw full 80psi for a long while on startup, then would go to about 45-50psi. And thats when the gauge isnt sitting on 0 :eek:
 

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Discussion Starter #7
The 98+ 6.5TD engines had a larger Higher volume oil pump that is a factory unit said:
I put a "longer" HV Melling pump in a worn 350. I understand what the extra volume does, basically fills up the gaps in the brgs. I don't think thast's the problemo with this motor. The oil stays too clean, and that's from 25 years of experience.
Should I check NAPA and similar for the '98 up? You'd think the AutoPartz listing would show the option. They don't... :exactly:
 

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I have changed my sender a couple of times over the years on my 84. reading scared the heck out of me. changed sender all was ok. when working funcky it would read way high sometimes past highest marks. it never read zero until it was shut off.
 
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