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Erratic oil pressure
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Rowroy
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PostPosted: Sun Feb 03, 2008 12:45 pm    Post subject: Erratic oil pressure Reply with quote

A little history . . .

My rebuilt 1776 has about 6500 miles since the rebuild. I'm using a CB "in & out" 30 mm oil pump w/ WIX filter. Also running 10W-30 Castrol GTX.


Recently, I've noticed that the oil light will come on occasionally when braking, accelerating, or turning (going around a bend). This has happened three times (oil level is fine), so I installed an Auto Meter pressure gauge.

According to the gauge, my cold pressure is ~50 psi @ ~2500 RPM. After warm up, the idle pressure is ~13 psi @ 1100 RPM and ~38 psi from 2000 RPM and up.

The pressure will drop to below 20 psi when cornering, braking, and accelerating. Once the speed has stabilized, it will return to 38 psi.

It's almost as though the oil level is too low, but it's not.

Also, I know that I should be seeing ~10psi/1000RPM, however, I can't generate anything above 38 psi no matter what RPM's I turn. Even @ 4500 RPM I still see 38 psi.

Any thoughts?
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runamoc Premium Member
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PostPosted: Sun Feb 03, 2008 1:03 pm    Post subject: Reply with quote

Did you put the stock oil filter back on? Sounds like your oil is sloushing to one side. Just because you have an external filter you still need the stock filter.
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Rowroy
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PostPosted: Sun Feb 03, 2008 1:31 pm    Post subject: Reply with quote

runamoc wrote:
Did you put the stock oil filter back on? Sounds like your oil is sloushing to one side. Just because you have an external filter you still need the stock filter.


Yes, I still have the stock screen in place.
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Randy in Maine
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PostPosted: Sun Feb 03, 2008 2:46 pm    Post subject: Reply with quote

Make sure there is no "burr" or "step" in the oil pressure valve hole. Brazillian oil pick up tubes are generally poorly thought of compared to a nice german one.

A stock 26mm pump would be better than the 30 you have also.


Been here?

http://www.thesamba.com/vw/forum/viewtopic.php?t=114496&highlight=oil+pressure
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PostPosted: Sun Feb 03, 2008 3:44 pm    Post subject: Reply with quote

Sounds like starvation, but 20 PSI should not be low enough to cause the light to flicker...have you reaplced the idiot light sender? They are normally notorious for turning the light on at very low pressures.
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Jimmy111
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PostPosted: Sun Feb 03, 2008 4:15 pm    Post subject: Reply with quote

I got to disagree with you Randy. The step is there for a reason. The step should be reamed to exactly 15.95mm The hole is 16mm and the piston should be 15.93mm If you ream the hole to 5/8" you will increaase the oil that will flow thru the valve as much as 1 gallon per minute.
A 21mm pump will flow all the oil that the motor needs. When the pressure control valve was installed they increased the pump to 26mm to compensate for the oil that was flowing thru the comtrol valve. With a 30mm pump there should be about 30% more oil than the motor really needs.
The motor should build about 10psi per 1000 rpm .If 38psi is the max expecially with a 30mm pump there is a big leak somewhere.
If the piston does not fit, clean it with some sand paper or replace it.
Warm up the motor then remove the cap from the oil control valve. let the oil drain out. put the cap back on and starrt the motor. let it run for a little while and then shut it off. Open the cap. there shoiuld be no oil or just a little oil there. If you have a lot the piston is leaking.
If you suspect the valve is not holding pressure, get a used piston and weld it to a piece of round stock. Use some lapping compound and lap the valve seat just as you would do your cylinder valves.
Usually if you have that big of a leak, it is leaking past the oil pump into the case or a lifter or 2 ground away their journals.

Check the in and out oil pump cover for wear first.
Then check the oil valves.
Next is motor disassembly.
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Rowroy
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PostPosted: Sun Feb 03, 2008 4:45 pm    Post subject: Reply with quote

miniman82 wrote:
Sounds like starvation, but 20 PSI should not be low enough to cause the light to flicker...have you reaplced the idiot light sender? They are normally notorious for turning the light on at very low pressures.


The light doesn't come on @ 20 psi. It only came on on three separate occasions, prompting me to install the pressure gauge.
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Rowroy
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PostPosted: Sun Feb 03, 2008 4:49 pm    Post subject: Reply with quote

Jimmy111 wrote:
I got to disagree with you Randy. The step is there for a reason. The step should be reamed to exactly 15.95mm The hole is 16mm and the piston should be 15.93mm If you ream the hole to 5/8" you will increaase the oil that will flow thru the valve as much as 1 gallon per minute.
A 21mm pump will flow all the oil that the motor needs. When the pressure control valve was installed they increased the pump to 26mm to compensate for the oil that was flowing thru the comtrol valve. With a 30mm pump there should be about 30% more oil than the motor really needs.
The motor should build about 10psi per 1000 rpm .If 38psi is the max expecially with a 30mm pump there is a big leak somewhere.
If the piston does not fit, clean it with some sand paper or replace it.
Warm up the motor then remove the cap from the oil control valve. let the oil drain out. put the cap back on and starrt the motor. let it run for a little while and then shut it off. Open the cap. there shoiuld be no oil or just a little oil there. If you have a lot the piston is leaking.
If you suspect the valve is not holding pressure, get a used piston and weld it to a piece of round stock. Use some lapping compound and lap the valve seat just as you would do your cylinder valves.
Usually if you have that big of a leak, it is leaking past the oil pump into the case or a lifter or 2 ground away their journals.

Check the in and out oil pump cover for wear first.
Then check the oil valves.
Next is motor disassembly.


Is that the front or rear valve? . . . I can never remember.
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Jimmy111
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PostPosted: Sun Feb 03, 2008 5:48 pm    Post subject: Reply with quote

The valve nearest the flywheel. The other valve is just a oil cooler bypass. But the piston should fit well in there too and not leak.
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PostPosted: Sun Feb 03, 2008 6:19 pm    Post subject: Reply with quote

Rowroy wrote:
miniman82 wrote:
Sounds like starvation, but 20 PSI should not be low enough to cause the light to flicker...have you reaplced the idiot light sender? They are normally notorious for turning the light on at very low pressures.


The light doesn't come on @ 20 psi. It only came on on three separate occasions, prompting me to install the pressure gauge.



I see, and when the light came on, what was your RPM doing? Does your RPM drop off around turns (float bowl sloshing), or do you notice that the light comes on any other times? Do you have a center mount carb, or duals?

My Corvair almost dies sometimes going around a corner, and the pressure light definitely comes on at those times.
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Rowroy
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PostPosted: Sun Feb 03, 2008 8:16 pm    Post subject: Reply with quote

miniman82 wrote:
Rowroy wrote:
miniman82 wrote:
Sounds like starvation, but 20 PSI should not be low enough to cause the light to flicker...have you reaplced the idiot light sender? They are normally notorious for turning the light on at very low pressures.


The light doesn't come on @ 20 psi. It only came on on three separate occasions, prompting me to install the pressure gauge.



I see, and when the light came on, what was your RPM doing? Does your RPM drop off around turns (float bowl sloshing), or do you notice that the light comes on any other times? Do you have a center mount carb, or duals?

My Corvair almost dies sometimes going around a corner, and the pressure light definitely comes on at those times.


My engine speed was steady @ about 2800 RPM's all three times. Also, I noticed that all three times the light came on I was going through a sweeping right-hand turn.

I have dual carbs.

_______________________________________________________

I'm going to start by taking Jimmy111's advice and inspect the pump cover and pressure control valve.

Is it possible that a fatigued pressure control spring could cause this problem?
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Rowroy
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PostPosted: Sun Feb 03, 2008 8:36 pm    Post subject: Reply with quote

Okay, I just went back and read Tom Wilson's write up on the pressure control and pressure relief valves and it got me thinking . . . .

According to him, the oil pressure control valve is supposed to open @ 42 psi. That leads to another set of questions:

1. Should a 30 mm pump be able to pump more than the pressure control valve is capable of flowing? If not, then I would think that the oil pressure would never get above 42 psi.

2. Are the "in and out" pump covers restrictive enough to limit enough oil flow that it could never generate more than 42 psi even with a 30 mm pump?
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Jimmy111
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PostPosted: Sun Feb 03, 2008 8:45 pm    Post subject: Reply with quote

The 30mm pump does pump more than the valve can regulate properly. But that just resulte in excessive pressures. Happens all the time. The 42 PSI is if everything is stock. People change springs, pistons, machine the piston seats and other Bright ideas and it all effects the pressure that the valve will open and close at. The 30mm pump pumps a LOT of oil. It is backed by a 40-200hp motor so pressure is not a problem. If the pressure isnt vented somewhere something will break. Usually the hoses or filter or oilcooler but cases crack too.

The whole Idea of the pressure control valve is to lenghten the service life of the motor by being able to supply more oil as the motor wears out. as the motor wears more oil will flow around the bearings and less oil will flow thru the controll valve untill no more oil flows thur the control valve and the oil pressure starts to drop.
The control valve is not a pressure regulator but more of a waste gate.
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bugninva
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PostPosted: Sun Feb 03, 2008 9:22 pm    Post subject: Reply with quote

Rowroy wrote:
[

My engine speed was steady @ about 2800 RPM's all three times. Also, I noticed that all three times the light came on I was going through a sweeping right-hand turn.



I'm with mini, it sounds like oil starvation....a 30mm pump, no add on sump, and a right sweeper are a very good recipe for pumping the sump dry...
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PostPosted: Sun Feb 03, 2008 9:29 pm    Post subject: Reply with quote

bugninva wrote:
Rowroy wrote:
[

My engine speed was steady @ about 2800 RPM's all three times. Also, I noticed that all three times the light came on I was going through a sweeping right-hand turn.



I'm with mini, it sounds like oil starvation....a 30mm pump, no add on sump, and a right sweeper are a very good recipe for pumping the sump dry...


It's probably all in his left side valve cover by the time the light flickers.
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bugninva
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PostPosted: Sun Feb 03, 2008 9:31 pm    Post subject: Reply with quote

miniman82 wrote:
bugninva wrote:
Rowroy wrote:
[

My engine speed was steady @ about 2800 RPM's all three times. Also, I noticed that all three times the light came on I was going through a sweeping right-hand turn.



I'm with mini, it sounds like oil starvation....a 30mm pump, no add on sump, and a right sweeper are a very good recipe for pumping the sump dry...


It's probably all in his left side valve cover by the time the light flickers.

exactly!
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PostPosted: Sun Feb 03, 2008 10:04 pm    Post subject: Reply with quote

Yes but that does not explain the low oil pressure on the straights and at standstill
Where is the oil then?
Should be in the case. So the 38psi indicates another problem.
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PostPosted: Sun Feb 03, 2008 10:44 pm    Post subject: Reply with quote

i don't see a huge problem with his hot pressures...he's running 10w30 which will flow quite nicely when hot, and that means it can be being bled off at the control piston, or he may have some loose tollerances...the 42psi magic number on the stock spring is assuming the spring isn't softer than normal from years of use... if the oil starvation happened at higher rpm's there always a chance bearings were damaged and this could cause lower pressure...I still say the reason was starvation, not to say that that didn't cause other problems..
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PostPosted: Sun Feb 03, 2008 11:34 pm    Post subject: Reply with quote

Starvation through acceleration and cornering means you need to add a sump.

If you need to machine your pressure control and pressure relief valve bores you can rent the tool from aircooled.net - at least they used to.

Good pressure is 10lbs for each 1k rpms
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Rowroy
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PostPosted: Mon Feb 04, 2008 6:07 am    Post subject: Reply with quote

bugninva wrote:
i don't see a huge problem with his hot pressures...he's running 10w30 which will flow quite nicely when hot, and that means it can be being bled off at the control piston, or he may have some loose tollerances...the 42psi magic number on the stock spring is assuming the spring isn't softer than normal from years of use... if the oil starvation happened at higher rpm's there always a chance bearings were damaged and this could cause lower pressure...I still say the reason was starvation, not to say that that didn't cause other problems..


I was wondering about this myself. God only knows how many times the pressure dropped to below 20 psi while the engine was spinning at 4500 RPM's during hard acceleration.

I wish I would have installed a pressure gauge sooner. Mad

Quote:
Starvation through acceleration and cornering means you need to add a sump.


I thought of this as well, but am afraid that it would fix the problem by masking the real issue. However, if the sump truly is being "pumped dry", then it sounds like I have no other option.
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