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  #1   IP: 199.116.74.233
Old 08-14-2017, 05:26 PM
clark800 clark800 is offline
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Gradually falling oil pressure

I'm having a problem with the oil pressure on a recently rebuilt late model Atomic 4 engine, about 3 hours since the rebuild by a very experienced mechanic. I'm using SAE 30W oil and the oil pressure gauge, oil pressure sender, and wiring are all new. The pressure starts out high at 75PSI cold, but over time the pressure gradually falls to 11PSI after 1 hour at 1600RPM (this is where I ended my test).

I've read that problems with the oil pressure relief valve can cause symptoms like:
- a decrease in oil pressure when adjusting the valve to increase oil pressure
- oil pressure decreasing as RPM increases
but this doesn't sound like the problem I'm having.

I'm going to try to find a mechanical pressure gauge to verify the readings, but I'm not too hopeful that this is just a faulty gauge because of the pattern of the readings.

I saw a part in the catalog that says:
"When the output from an oil pump drops off below a certain point, oil pressure will decay over several hours of operation even though all bearing clearances are normal. When this condition occurs, the problem is seldom excessive wear on the oil pump gears themselves, but wear within the housing of the rear main bearing cap in which the gears rotate (including the four holes in the housing which serve as bearings for the rotating shafts of the gears)."

This sounds like it could be the problem I'm having; is this something that is likely to be missed in a rebuild? Is there anything else I should consider? Could this be due to a faulty spring in the oil pressure regulator?

I've attached the pressure, temperature, and RPM data from a 1 hour test run where it started in neutral for 10 min, then shifted to forward and I increased the throttle a bit at 15min.
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Old 08-15-2017, 09:59 AM
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Clark800,

Definately get a mechanical gauge to confirm. It will probably still show the gradual decline in pressure but the numbers will be more accurate.

How did the oil pressure behave before the rebuild?

Were the crank journals correctly measured, machined as necessary,and the bearings replaced?

How about the cam bearings which are often overlooked during A4 rebuilds? Along with crank and rod bearings, cam bearing clearances play a big part in oil pressure, particularly as the oil heats up and thins.

Switching to 40W or 20-50 will help. As long as your maintaining 10lbs per 1000 RPM, you'll be OK.

I'm particularly curious about your dilemma as i had the same exact issue once.
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Old 08-15-2017, 10:55 AM
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Is that water or oil temperature on your graph?
Falling pressure would normally be caused by one of two basic causes:
1. Something wrong with the pressure control valve.
2. Oil too thin for the bearing clearances.

Number 2 can be caused by worn bearings or oil being too thin. Oil can be too thin because you put the wrong kind in or because it is too hot.
You might start with different oil - I have very good results with Shell Rotella 15w-40. If nothing else, the results might be educational. Before I even did that I would take the pressure valve out and make sure all is well.

Last edited by joe_db; 08-15-2017 at 11:02 AM.
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Old 08-15-2017, 11:36 AM
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I agree with Joe.

A multi-vis oil may be in-order.

A "very experienced mechanic" still has to make judgement calls on the wear tolerances of parts, and some he measured may be on the high range of acceptable clearance.
That, combined with poor quality oil, low volume of oil, and high temp(of oil) may all be contributing to low pressure in their own little way.

Cheers,
Russ
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Last edited by lat 64; 08-15-2017 at 11:00 PM. Reason: typos
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Old 08-15-2017, 12:06 PM
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I have a pretty worn out engine, and burn a little oil thru the #4 cylinder...I've run thru almost every different type of oil we've ever discussed here, and I am presently running Shell Rotella synthetic 5w-40. I get pressures a little higher than I'd like when cold (60+), but it settles down to 35-40 when warmed up for the duration of the trip. I do have the Indigo oil filter and included pressure regulator remotely mounted, and have bottomed out the stock regulator in the block.

All the things mentioned above sound like good details to talk to the mechanic about to help confirm or deny your findings.
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Old 08-15-2017, 12:06 PM
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Quote:
Originally Posted by lat 64 View Post
I agre with Joe.

A multi-vis oil may be in-order.

A "very experienced mechanic" still has to make judgement calls on the wear tolerances of parts, and some he measured may be on the high range of acceptable clearance.
That, combined with poor quality oil, low volume of oil, and high temp(of oil) may all be contributing to low pressure in their own little way.

Cheers,
Russ
+1
Don't forget - hot 15W40 is *thicker* than straight 30 weight when hot
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Old 08-15-2017, 12:28 PM
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Other than a change in the viscosity of the oil, or loss of oil, what would explain the change over time?

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Old 08-15-2017, 01:12 PM
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Quote:
Originally Posted by Administrator View Post
Other than a change in the viscosity of the oil, or loss of oil, what would explain the change over time?

Bill
Some part of the engine increases clearance over time, which is backwards to how it usually works AFAIK.
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Old 08-15-2017, 02:16 PM
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Just curious... Mechanical fuel pump?

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Old 08-15-2017, 03:18 PM
JOHN COOKSON JOHN COOKSON is online now
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I'd do a couple of things.
Confirm the OP readings with a mechanical gauge as mentioned.
See if you can change the OP with the adjustment device when the readings get squirrely. If you can't influence the OP with the adjustment then the ball may be off center on the spring or the seat may be not correct. MMI used to sell a tool to dress the seat. I don't see it in the online catalog. Maybe I'm not remembering correctly......

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Old 08-15-2017, 04:34 PM
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I had a similar problem after rebuilding my engine. I could set the oil pressure before the engine warmed up, but then it would drop like a rock once the engine warmed up. I could then adjust it back up, but the gauge would peg high when starting cold. I purchased the cone style pressure valve from MMI, this helped a little but pressure was still too high when cold and too low when warm. The problem was most likely damage to the valve seat for the oil regulating valve. I installed the indigo oil filter/pressure regulator and now the oil pressure stays at 40 psi under all conditions.
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Old 08-15-2017, 08:53 PM
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Quote:
Originally Posted by JOHN COOKSON View Post
MMI used to sell a tool to dress the seat. I don't see it in the online catalog. Maybe I'm not remembering correctly......

TRUE GRIT

Product No. - TOOL_05_172

at http://www.moyermarine.com/cgi-bin/s...rebuilder.html

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Old 08-16-2017, 10:21 AM
clark800 clark800 is offline
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Thanks so much for all the advice! I'm on vacation now, so I won't be able to test anything for a while, but I'm looking forward to trying these recommendations.

To answer some of the questions:
- I bought this engine after the rebuild, and I haven't heard from the mechanic recently, so I'm not sure what it was like before the rebuild.
- The temperature graph is for the water temperature. I thought about this ambiguity right after I posted
- The engine has a mechanical fuel pump. Does this have an influence on oil pressure?

The Indigo kit sounds like an interesting option, but I'm a little confused about how it works. It says it connects to the oil sender port, so does that mean the stock oil pressure regulator stays in place and works in parallel? Wouldn't that mean installing the kit could only lower the pressure by providing an additional relief point? Or can it be installed in place of the stock regulator?
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Old 08-16-2017, 10:36 AM
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The original oil pressure regular gets plugged when installing the Indigo oil filter. The oil pressure is then easily adjusted by a pressure regulator on top of the oil filter housing.
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Old 08-16-2017, 10:57 AM
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From the "Long Shot" Department:

You have a mechanical fuel pump. When the diaphragms in these pumps begin to fail, they leak fuel (by design) into the engine oil. If this were happening, the presence of the gasoline would surely kill the viscosity of the oil. The longer the engine runs under these conditions, the worse the effect.

Two quick checks:
  1. Sniff the oil dipstick for the presence of gasoline.
  2. Check the oil level for anything suspicious. In severe cases, the level might actually rise with the addition of the fuel.

Other, wiser members will amplify or correct as needed, please.

Bill (Admin and Forum Executive Vice-President in charge of long shots)
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  #16   IP: 72.194.218.136
Old 08-16-2017, 02:54 PM
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Quote:
Originally Posted by Administrator View Post
From the "Long Shot" Department:
You have a mechanical fuel pump. When the diaphragms in these pumps begin to fail, they leak fuel (by design) into the engine oil. If this were happening, the presence of the gasoline would surely kill the viscosity of the oil. The longer the engine runs under these conditions, the worse the effect.
Two quick checks:
  1. Sniff the oil dipstick for the presence of gasoline.
  2. Check the oil level for anything suspicious. In severe cases, the level might actually rise with the addition of the fuel.
Other, wiser members will amplify or correct as needed, please.
Bill (Admin and Forum Executive Vice-President in charge of long shots)
I'll see your bet and raise.
Using heaver weight oil might give a satisfactory gauge reading while the root problem remains.
I would be more in favor of trying to find the root problem and then use heavier oil as a last resort. There have been several suggestions made. What has been the result after trying them? Don't remember seeing any result reported (I didn't reread the thread)
My A4 was placed in service in 1980. Oil pressure is still perfect using straight 30 weight oil.............


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Old 08-16-2017, 03:16 PM
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I think you may have confused my comments with someone else's.

I made no mention of using a heavier weight oil. I was simply suggesting a possible root cause (leaking diaphragm) which could become more suspect or discounted altogether by means of a couple of 15 second tests.

The degradation over time was, I thought, an important observation, possibly explained by a significant degradation in viscosity, which might in turn be explained by the introduction of gasoline.

Bill
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Old 08-16-2017, 04:48 PM
JOHN COOKSON JOHN COOKSON is online now
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I was speaking in general that it would be better to identify the cause of the wobbly oil pressure. Quoting you didn't help make that point clear. Sorry 'bout the confusion.

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Old 08-25-2017, 11:35 AM
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Yeah, I would like to figure out the root cause before resorting to multi-weight oil.

I smelled the dipstick and there was a non-oil odor, but I'm not sure if it was a gasoline odor, it smelled more like the odor the engine gives off when it's running, which my neighbor said was normal for new engines. He said it was probably the paint off-gassing due to the heat of running.

I have not noticed any increase in the oil level on the dipstick. Also, my oil pressure returns to high levels after each cold start and follows the same gradual fall each time. If gasoline was leaking into the oil, would the gasoline evaporate out over time or stay in the oil? If it stays in the oil and accumulates, then I can probably rule it out as the issue; if it evaporates out, then I would have to test immediately after running for a while.

I just ordered the Indigo Oil filter, which will allow me to eliminate all factors related to the oil pressure regulating valve from the experiment. I'll report the findings next week.
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Old 08-29-2017, 12:21 AM
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I installed the Indigo oil filter and a mechanical pressure gauge; it turned out that the (brand new) electrical gauge was off by as much as a factor of 2 from the mechanical gauge, but the oil pressure problem persisted.

The oil pressure was steady for a few minutes around 35PSI, but after running for an hour, the pressure reading on the mechanical gauge had dropped to 16PSI at 2000RPM, 14PSI at 1800RPM, 12PSI at 1600RPM, 10PSI at 1400RPM, and 5PSI at 1000RPM, with a water temperature of around 175F. All the readings on the electrical gauge were about half of these. Tightening the adjusting screw on the Indigo oil filter did not seem to have any effect on the oil pressure at the end of the test, though it did at the beginning. At the end, the pressure seemed to be holding steady at these levels.

It seems like it might be an issue that requires taking the engine apart to fix. I guess I will try the multi-weight oil now.
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Old 08-29-2017, 12:33 AM
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Have you tried he oil pressure adjusting dohicky seat? Post #12.

TRUE GRIT
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Old 08-29-2017, 10:14 AM
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Quote:
Originally Posted by clark800 View Post
I installed the Indigo oil filter and a mechanical pressure gauge; it turned out that the (brand new) electrical gauge was off by as much as a factor of 2 from the mechanical gauge, but the oil pressure problem persisted.

The oil pressure was steady for a few minutes around 35PSI, but after running for an hour, the pressure reading on the mechanical gauge had dropped to 16PSI at 2000RPM, 14PSI at 1800RPM, 12PSI at 1600RPM, 10PSI at 1400RPM, and 5PSI at 1000RPM, with a water temperature of around 175F. All the readings on the electrical gauge were about half of these. Tightening the adjusting screw on the Indigo oil filter did not seem to have any effect on the oil pressure at the end of the test, though it did at the beginning. At the end, the pressure seemed to be holding steady at these levels.

It seems like it might be an issue that requires taking the engine apart to fix. I guess I will try the multi-weight oil now.
What did you do with the original oil pressure adjuster?
Also note a mismatched sender/gauge combo can have effects you described on the electrical gauge, i.e. a 60 PSI sender on a 120 PSI gauge or some other mismatch.
Is it possible the oil pump itself needs work? I think it can have an issue with excessive clearance that would drop the pressure as it warms up for sure.
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Old 08-29-2017, 12:33 PM
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Quote:
Originally Posted by JOHN COOKSON View Post
Have you tried he oil pressure adjusting dohicky seat? Post #12.

TRUE GRIT
John,
If he followed the Indigo installation instructions, there are supposed to be parts included in the filter kit to "bottom-out" that adjustment, so that you can use the more accessible adjustment assembly in the kit. I mounted mine on a bulkhead along with the filter housing.
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Old 08-29-2017, 05:25 PM
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Well, the Shell Rotella 15W40 oil did not help. After running for 40 minutes, the oil pressure was 14PSI at 2000RPM, 12PSI at 1800RPM, 11 PSI at 1600RPM, 10PSI at 1400RPM and 5 PSI at 1000RPM, according to the mechanical gauge (basically the same as before). Of course I only put in about 3 quarts because that's all I could pull out of the dipstick tube, but it seems unlikely that more oil changes will improve the issue.

I also noticed that a lot of smoke starts coming out of the oil fill cap as the engine warms up. The smoke tests positive for carbon monoxide. I'm not sure if this is related.

As a side note, the electrical oil pressure sender and gauge are both 0-80PSI and I'm pretty sure they are compatible; they are both Sierra brand. The electrical and mechanical oil pressure gauges match nearly exactly for the first 15-20 minutes, but seem to diverge as the temperature warms up.

Regarding the Indigo Oil filter kit, it comes with a plug to replace the stock oil pressure relief valve. I removed the stock spring and inserted the plug which consists of a sphere (like the new-style relief valves), a cylindrical spacer, and a bolt to tighten in place. I have it closed off very tightly with the bolt.
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Old 08-29-2017, 07:45 PM
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clark800, Referring to the old regulator, did you get the OEM ball out that is also in the stock pressure regulator? That is the piece that the spring would be pushing on in a late model block. Just want to make sure you don't have two spheres in there!
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