4106 Low Oil Pressure

[Madmike]

I have a 4106 with 8v71 engine. The gauge on the dash read very low oil pressure. It goes from around 25 down to just above zero. It has been very hot here and I am running 40wt as recommended. I also seem to get big puff of white and black smoke when I take off and in second when I first hit the gear. On the hwy she still runs smooth and will go 70 easy. There is also a gauge on the engine that looks like it is half filled with oil that reads about the same as the one on the dash. I do notice that when stopped an idling you can see oil dripping, not a lot but it sure makes a mess on the street in front of my house.

[Dreamscape]

Our 8v71 during the hot summer months reads about 10-15 lbs at idle, 60 at full load until she gets to normal operating temp then drops down to around 45. If your temps are normal for this time of year, I wouldn't worry too much.

Depending on where the leak is coming from, might check your slobber tubes. Do you have a catch can hooked up to them?

BTW, ours leaks a little dino too! Just enough to mark our territory.

Paul

[lostagain]

You have some oil pressure, that's good! Don't worry about it. Keep an eye on it though. The low pressure warning is set at around 7 psi. That would light up the flashing idiot light in the dash, and shut you down if the system works as designed. Before you start it, with ignition on, the warning light should be on, then go off as soon as it runs and builds pressure beyond 7 or 8 psi.

Your engine sounds like it is tired. Lots of miles on it? New rod and crank bearings would up the oil pressure. You could also check the oil pump bypass spring, it might be weak. Put a washer or a coin under it to make it longer/stiffer.

Keep driving it...

JC

[gm4106]

Try changing the gage in the back to a good gage you know that is working right. If I remember right, I heard the block the gage goes to and the line to the alt. - gen. will have a effect on the gage reading low.


OneLapper
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   Low Oil Pressure on 4106
« on: March 26, 2007, 10:38:13 PM » Quote 

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Hey People,

I have driven the bus about 4000 miles but never had a working oil pressure gauge up until recently.  When I got both the electrical and mechanical guages working, the engine showed only 10 psi going down the road.  This got me worried.

Here is some info on the 4106 8V71 low oil pressure.  After work today I rigged up an adaptor using the mechanical oil pressure gauge on the oil manifold and attached it to the hose coming from the block to the tee fitting on the engine generator.  This test took the generator out of the oil pressure loop and let me check the oil pressure coming directly from the engine block.  The results: Oil pressure used to show 10 psi cold idle when connected to the generator.  When bypassed, cold idle is 55 psi! Ah ha!

The previous owner told me he install a used generator when the original one went bad.  The orginal came with the bus along with an extra starter, wiper motors, new lenses, windows, etc.  I pulled out the generator and promptly called Luke at US coach.  He confirmed that the original generator's back plate has a small hole cast into it to act as an oil flow restrictor.  I removed the back plate and he was spot on, a small orfice, maybe .050" cast into the back plate where the oil supply tee/hoses attach.  In short, the gernerator currently on the engine is not specifically for this application, although it does fit on a 8V71.  Luke mentioned to swap back plate and that will correct the low oil pressure reading. That's tomorrow's task.

Sorry for the long post, but I figured that this info might be of some interest to you all.

Mark
'64 4106

[buswarrior]

Dash board gauges in a new to you coach are best to be regarded as useless, until they are proven to indicate something, and then, usually, it is something relative, not something accurate in regard to the numbers on its face.

If your automobile had a couple million miles and 20-30-40-50 years of service, nothing in the dashboard would be reliable either...

happy coaching!
buswarrior

[Bob & Tracey]

Our 8V71 reads as yours does, both on the dash and at the rear. I replaced the rear gauge with no change in the readings. I then found that the gauge line was teed into the oil line going to the alternator. I then took the alternator out of the circuit allowing full pressure to the gauge, 35psi at idle and 60 at speed. I was then advised to check the alternator for orifice at the inlet (I don't remember the size) and it had that. My conclusion is that there should be a better way to pipe the pressure gauge with a dedicated source off the engine block. Any thoughts about suppling the alternator and air compressor from the same source at the block?

Yes, I did return the plumbing to it original set up.
Bob

[Madmike]

Great Info. I will check it out more when I get back to the bus. The low oil light does come on when I first start the bus but that is it. I just don't want to be IG and mess somthing that is expensive up. The temp gauge does not work either and that light does not come on so I am very conserned about it but right now I at a dead end. I know she is very old but on the hwy she rolls very smooth and nice, I just hope I can keep her running that away.
Right now it is just so hot it is impossible to do to much to it with out getting heat stroke.

[bevans6]

I had the same experience with the alternator being fed from the same line as feeds the oil pressure sensor.  How I fixed it below.  I recommend that, as a test, you remove the oil feed line to the alternator and plug it, run the engine and see what oil pressure you get with the feed to the alternator  disabled.  Delco states that is acceptable for testing up to 100 amp draw, so no worries unless you leave it disconnected for weeks on end.  My result was 60 psi hot high idle and 25 psi  idle.  Two ways forward - one is to relocate the pressure reading sensor to a different oil line, some have suggested the line on the other side of the block for the compressor.  What I did is to take a line adaptor of appropriate size, braze it closed and drill a  .0625 (1/16") hole in it to simulate the .050" restrictor mentioned in the alt. back plate.  Before I did that I researched the oil flow requirement of a DN50 on the Delco web site, and calculated (well, google found me a calculator and I plugged in numbers) the oil flow through an orifice at 50 PSI to make sure the restriction would flow the correct amount of oil to the alternator per the Delco data sheet. 

Anyway, hope this helps a bit.  I now have 45 psi hot pressure on my dash gauge, up from 25 psi, but I know why, and that makes the difference.

Brian