Low Hot oil pressure (what is wrong?)

[rfb6435]

Ok so my new rebuild was running fine and suddenly dropped oil pressure at idle when I came off a freeway ramp... Both the light came on and the guage started to fall. I then installed a mechanical guage and can see the oil pressure really drop off when the engine gets warm. Cold it had 30psi or so and then it dropped to ~8psi at idle and was still falling.

I had ~15 miles on the rebuild from my last failure...

Here is the story:

I had an engine built a few years back and it sat around for until this summer. I finished putting it together primed it up and everything seemed fine. I then lost oil pressure and all of the bearings were destroyed. I felt it was the oil pump, my machinist said it was because I didn't prime it well enough and the assembly lube had dried out blah blah.

I then had it rebuilt (along with the turbo) and then gave it another go. I carefully primed the engine, etc and now I am in the same place again.

One strange note is that I have never had any lifter noise in either failure. The head doesn't appear to lose pressure.

I removed the head and see that there is a bit of skuffing in the bores.

• I used a new Mopar oil pump, new oring on the pickup, anerobic sealer between the pump and block.
• The engine is a 2.2 crank in a 2.5 common block w/ the balance shaft hole plugged.
• The crank was turned, the rods resized all new rod and main bearings...
• The bores were honed and clearances checked.
• The intermediate shaft bearings were installed and inspected on the rebuild.
• The oil restrictor is installed.
• The distribution block isn't overtightend (that would lead to lack of oil to the head rather than the block anyway)
• The turbo feed line was clear so nothing came from it.
• The engine was primed w/ a wrench, there was plenty of oil comming out the cam caps, out the turbo feed line, etc.

The oil does not appear to have any metal in it yet but something is really wrong.

What else should be checked?!?!!?!?

My oil feed line to the turbo is AN4 but I modified the distribution block to take a 1/8" NPT direct to AN4 by chopping off the inverted flare fitting and tapping it. Does this make the line too big and steal too much oil from the bottom end (doubtful but I am racking my brain)?

I am not sure if there is an oring behind the oil filter check valve/insert. I didn't think there was one there but one of my books showed one. Is there supposed to be one? If not would it even matter since any leak would still have to go back into the oil gally...

Anyway it happend twice so there is something definately wrong.

-Rich

[Moparbishi]

are you reading the stock gauge or aftermasrket?

[rfb6435]

Started with stock, then installed an aftermarket mechanical. Both drop off significantly when it gets warm.

[2.2=8]

It is normal to loose aprox. half your oil psi. from cold engine verses hot engine.

what are your main and rod brg. clearences?

How much clearence do you have between the oil pickup sceen and oil pan floor?

What type and viscosity oil are you using?

How much oil pressure do you have at 3000rpm Hot engine?

What oil filter are you using?

The factory service manual states......OIL PRESSURE-ALL 2.2-2.5....ENGINE FULLY WARM....@ curb idle-4 psi. @ 3000 rpm-25-80 psi., I just copied that directly from the manual..........My 84 manual says min. idle psi is 2psi hot.

Never assume anything about clearences just cause a machine shop did the work, except you can ASSUME they got it wrong. ALWAYS double check the work!!! Not saying they are all bad, I mean everyone can make a mistake.

If the engine is quiet and NO rattles it may be just fine

If everything is normal and you want more psi you could remove the pump and shim the bypass spring, but only after you check every other possibility.

[adrenlen]

my motor is about 2 seasons old but not long after break in my hot oil pess. at idle was only about 6-7 psi. Enough so the light won't come on but I did the same thing with the after market gauge because the stocker was scaring me. My stock sending unit does a funny twitch under certain vibrations at wide open throttle. Not something you want to see at 5k rpm is your oil press. drop alot.:(

[phantomrt]

Minimum hot oil pressure spec is 4 PSI, but we all can admit that is VERY low. Thats a lower spec than for anything else I've had to deal with. For a new engine, this pressure should be substancially higher than that. At 4 psi, is that enough pressure to shoot oil out of the rods and lube the cylinder walls sufficiently? Good question I think.

I have a feeling that the bearing clearances are not very tight--not as tight as they should for a rebuilt engine. Using 5w30 oil and when fully warmed up, 900 RPM idle should produce about 13-15 PSI. A more experienced engine builder could make a more accurate estimate, but I'd say the bearing clearances are at .005" or so... double what it should be.

How does the oil smell? Like gas? That'd lead to lower oil pressure. Not uncommon for a new engine, but that shouldn't happen in 15 miles.

I disagree with the machinist in saying the oil pump priming was the issue the first time around. The assembly lube is good enough for an engine to run 5-6 seconds easily with no oil pressure. If you do not get pressure in this amount of time, something is very wrong and at least some of the engine must come back apart. Plus, you can disassemble an oil pump and visually inspect everything for signs of wear, etc instead of just replacing it, assuming it is bad and indeed the ultimate cause of the bearing failure. Besides you did a plenty good job of priming it. Does anyone prime the oil pump after an oil change? It is essentially the same thing as starting a new engine. The 2.2/2.5 has a check valve to keep oil in the engine, but a LOT of engines out there have no such provision and they hold up fine.

If you have a crankshaft-driven oil pump, then what do you do?? Can't prime that without starting it.

[puppet]

What does the pressure do off idle? ... go up .. stay the same? Can't see how the head can have pressure if you don't have it at the distro block. Line to the turbo might seem like a problem at first glance but according to Chris at TU the bearing housing has a restriction built in. So, this shouldn't be an issue.
... anyway.
Besides checking the bearing clearances check the side clearances on the rods to the crank. Too much space here will do you in for sure. ( .005/.013" total, one rod)

[rfb6435]

The machinist said that the clearances bearings should have been .002-.0025. This was from his memory rather than looking it up. Of course he would look it up when building to verify.

[86Tona]

What about the clearances at the cam journals? If the machine shop did their job properly and we assume they did then the lower end is probably fine. That leaves the head and the cam journals.

[rfb6435]

Quote:

Originally Posted by 86Tona What about the clearances at the cam journals? If the machine shop did their job properly and we assume they did then the lower end is probably fine. That leaves the head and the cam journals.

I took him the head after the first failure and he checked to make sure they were ok. Can you lose that much pressure through the cam caps? It is a roller cam in a G head so it has the slots and is losing some extra but wouldn't that also make for a bunch of lifter noise?

[86Tona]

Not necessarily a bunch of lifter noise if the space between the cam journals and the cam is too great. Use some Plastigauge to measure these clearances to be sure they are not too great. If the crank is 0.002 - 0.0025 then (and I don't have my FSM in front of me) the cam journals should be similar. If even one of them is too wide then it may cause pressure loss when it gets hot.

[Reaper1]

Those clearances are a little on the loose side for a new engine IMHO. I set mine at about .0014-.0017.

[phantomrt]

Spec is something like .0015 to .0025 I think. I always get my crankshafts/bearings from the same place and the clearances always seem to be around .002... right on.

Oversized journal head maybe with a regular cam?

[86Tona]

OS journal head would be way too much 'clearance'. It's like .020 or something oversized. If this was the case I would think that the pressure would drop like a rock even if it's cool. Still if the head is OS and the cam is not it could account for the first failure at 15 miles as well as the current problem. Check the head for OS stamped in it. Since it's a G head it may be an OS head.

[puppet]

Quote:

Originally Posted by rfb6435 The machinist said that the clearances bearings should have been .002-.0025. This was from his memory rather than looking it up. Of course he would look it up when building to verify.

I know what your writing about but just to be clear .. I'm refering to the rod(s) side clearance. ... not the bearing clearance.