oil pressure fluctuations

[paolomarks]

I've got a vanagon with a newly rebuilt AAZ at 50deg,  K03 turbo properly plumbed and clocked, 19 row front mounted external oil cooler, saab 900 IC in the D pillar.  It has the original diesel tranny which I find perfect for these West Virginia mountain roads. When I venture out on the interstate I keep it at 55mph. 
   I have an electronic Oil Pressure Gauge with sender in the back of the head and an oil temp gauge reading from the filter housing.  55mph in 4th on my rig is about 3700rpm and at 200farenheit I have 60psi. Pressure goes up and down linearly with rpm.  Even on extended climbs my oil temp has never exceeded 210f and usually is 190ish. Water  measured at the head is around 180 normally , going up to 205 on the steepest of climbs.
    Changed the oil and filter 100 miles after the rebuild with rotella 15 -40( takes 7 quarts  with  external oil cooler and lines added.)  Ran it 3000 miles in 4 months with oil pressure as described above and then all of a sudden when cruising at a steady 55mph the oil pressure began to dip down to 40psi. It would stay there for a little while and then climb back up to 50 or 55.  (rpm steady all the while)  Oil temp was perhaps a few degrees higher than normal but never exceeding 215f. Oil level was fine. Oil pressure bounced around like this all the way home, never getting low enough that I felt I needed to shut the engine off, but concerning none the less.
   Once home I changed the oil and filter and Oil pressure returned to its previous levels and linearity.
    Did I have water in the oil?   Accumulated there because my oil temp rarely goes above 212f.       

Paolo.

[libbydiesel]

I have found on the vanagons that when the oil level in the pan is slightly low, oil pressure drops when boost pressure rises.  I believe that it is because the oil becomes aerated.  See if the two are related on your van.  If so, then try topping off the oil level and see if the fluctuations go away. 

[BoostedOne]

What kind of filter did you have?
May have just been a dud filter.  Back when I was young I worked for a year to build a motor for this Mustang I had.  The guy I used to hang around who was my Ford engine guru swore by Motorcraft filters and oil.  After I got the car going, I religously followed his advice.  Except once, about 10 months later.  In a pinch I bought a Fram. 
The car was 15 years old, and had factory electric gauges.  When I started the car after the oil change it didnt seem like the gauge went as high as it normally did.. Figured it was just old wiring, old gauge, stupid young kid optimism.  Kept thinking "I need to get some money for those Autometers"..
Well over the course of a week the pressure seemed to drop.  I had to take the car on a trip about 70 miles, and when I was down there I saw the gauge barely coming out of the L region(one of those L, Normal, H gauges)...  One the way home I said "Ah, let me buy a filter and just put it on and see what happens...

Got home, threw a new motorcraft filter on the car, gauge went back up close to H where it normally sat.  Figured all was great.. Drove through the neighborhood, got out onto the highway for a celebratory blast, and in a 2nd to 3rd gear power shift BANG!
Long story short, intake valve locked up in the guide, piston contacted the valve at 6000rpm, piston shattered, connecting rod immediately punched through the cylinder wall into the cooling jacket, which then all(or atleast a significant amount) of coolant was sucked through the open valve into the intake manifold to be distributed to the other cylinders which hydrolocked the engine at about 6000rpm.. The whole thing went from great to scrap in a split second...  When it was over the only things I sold off that engine was the external stuff..  Rods were junk, crank may have been good but not worth the risk.  Heads were pretty much junk because of all the damage to the chambers and seats from the chunks of piston getting smashed into them.

That was back in like 1993 or 1994... Since then you'd have to put a gun to my head to use a FRAM... 

[libbydiesel]

I only use OEM VW filters (Bosch, Mahle or Mann). 

[paolomarks]

  When I first saw the pressure slipping, I stopped immediately and checked the oil level.  It was slightly down so I topped it off.  It didn't help.  The fluctuations occurred as before and didn't seem to have any rhyme or reason to them.  As far as I could tell they were unrelated to boost, engine load,  oil temp, whether I was going up hill or down, etc.  For example it would  hot idle at 15psi  which has been about normal and as I accelerated through the gears and maintained 40mph in 4th , pressure would climb to  40psi but then all of a sudden drop to 20.  A minute later it might go up to 35(maintaining 40mph all the while)     
        I use Mann filters, and cut open the old one looking for clues, but didn't see anything unusual.     Paolo.
   

[theman53]

No clue on the brand of gauge you have but that could be suspect if it is a "cheaper" one. Also you said it was electric. I prefer manual gauges normally but like electrics on the oil pressure as no hot oil in the cab through a line that could spray you. That said electrics usually have issues when things are hot. I am not saying it is 100% electrical but checking the grounds and wiring in general may show you something that only pops up when you are really hot temp wise.

*EDIT* I would give it a shot that is if all that Libby says has been looked over.

[ORCoaster]

When I first started reading the OP problem I thought Bad filter.  Then I thought hmm 7 qts of oil I wonder how he gets all that out of the system or if he does.  Then there is the question is how does it all get back.  OK, I know oil pump does that.  But if it is like my setup only a partial flow goes to the aux. oil system so could air get built up in there and kick into the pan as foamy oil and cause the pump to be pulling in foam and not a liquid?  Since he did top off the oil I also did the think on the bane off all electrical stuff.

Ground Gremlins, little bass-turds I would be checking and cleaning connections if I were you.  Maybe that will do it.  Finicky sender unit?  Also foam into it?  Now that your oil has settled down, you have a proper filter. I would think you are good to go.  Just give the wires and nuts holding them a once over.

2 cents please

[masterbeavis]

In a pinch I bought a Fram.  
The car was 15 years old, and had factory electric gauges.  When I started the car after the oil change it didnt seem like the gauge went as high as it normally did.. Figured it was just old wiring, old gauge, stupid young kid optimism.  Kept thinking "I need to get some money for those Autometers"..
Well over the course of a week the pressure seemed to drop.  I had to take the car on a trip about 70 miles, and when I was down there I saw the gauge barely coming out of the L region(one of those L, Normal, H gauges)...  One the way home I said "Ah, let me buy a filter and just put it on and see what happens...

A 15 year old car with at least 150K on the odometer, factory idiot gauges that really are more like on/off switches, and a kid who religiously beat the tar out of the stock 302....   I bet you did something wrong to the motor, and after alot of abuse the motor really wasn't built to handle, decided to die coincidentally when you installed a Fram filter. Regular right foot input 6,000 RPM blasts for a stock 302 is begging for eventual trouble.  I've seen 302s last 300k with tons of abuse and minimal maintenance, and I've seen them make it to 100K and blow up for no reason...  

Back on topic...  I had a "new" rebuild 460 that had oil pressure fluctuations.  I put on several new pumps, high volume and STD volume, changed the main/rod bearings, checked their tolerances etc...  When I finally blew the motor up (it had detonation issues) I discovered one of the cam bearings were trying to spin..  The bearing material had been picked up and redeposited halfway across the bearing...   Based on the apples to oranges experience of having a similar problem on an American Big Block Ford, I would render a guess that you have something trying to go wrong in the bearing department (motor or turbo) or possibly a lifter?

What kind of oil are you running and how many miles were on the current oil when the problem started.  Have you considered having your oil analized?  Have you confirmed the condition of the turbo?  Was the oil pump new or used?  If any moving part has an issue, that could be the problem with your oil pressure.  I would be inclinced to verify your oil pressure conclusions with a manual gauge to eliminate any electrical problems as previously mentioned.

[BoostedOne]

A 15 year old car with at least 150K on the odometer, factory idiot gauges that really are more like on/off switches, and a kid who religiously beat the tar out of the stock 302....   I bet you did something wrong to the motor, and after alot of abuse the motor really wasn't built to handle, decided to die coincidentally when you installed a Fram filter. Regular right foot input 6,000 RPM blasts for a stock 302 is begging for eventual trouble.  I've seen 302s last 300k with tons of abuse and minimal maintenance, and I've seen them make it to 100K and blow up for no reason...  

Actually the 79 Mustangs had actual gauges.. the idiot light gauges didn't come along until later....
Engine wasn't a stock 302... The was was originally a 4 cyl car someone gave my brother when they seized the engine.. Then he gave it to me.  And as mentioned, I spent a year working to afford the engine that was in it.. It was nothing spectacular, but it was a rebuilt 351W.  Bottom end was built by a local Ford only guy who knew his stuff..  Need tunnel port FE parts?  He had a bunch..  Aussie cleveland heads, he had that stuff too..  Decent amount of money was spent at the machine shop on the bottom end..Crank was fresh, pistons were new, etc. Top end had some cleaned up mild ported 289 heads, stock size valves, with a valve/guide job.  Can't remember what springs we put on it, this was 20 years ago.  Mild crane cam, Holley Street Dominator intake, just a basic setup. 
Setup had about 8-10K miles on it when it blew up.  Sadly it blew up a week before Fall semester at school started so I parted it out to buy a Scirocco from my freind so I had a car to get to school...

But this wasn't a clapped out 302 that lived its life being beat within inches of its life.. It was a high 13 second car, a walk in the park for a Windsor.

You can bet I did something and make all the assumptions you want..  You are also welcome to gamble all you want with Fram's stuff, its your money.  Interestingly enough Fram has a crap reputation on any web board I ever been on, but I have had that opinion for 3 years before I ever got on the internet...

[8v-of-fury]

I have run Fram for years now, and my guru has also done the same since the 80's.. GRANTED, they have come alongway since 1993

Have you actually looked at them recently? Great construction, and superb filter material. Knocking FRAM is so pre-1995. Get with the program old timer! I am kidding, calm down. lol

Honeywell makes Fram nowadays, and my brothers shop uses another Honeywell no name for ALL their oil changes. Literally 10-15 cars a day, all year long, for the last 15+ years have been getting the no-name filters. Never, have they had a call back from a blown up oil deprived engine. (simple math puts that at over 50,000 Fram filters distributed from one shop alone with no call-backs due to issues with the filter)

No offence, but your one time bad experience is not nearly as definitive.

[theman53]

I won't use fram either. I have seen them cut apart recently and they do not hold a candle to a Mann or Mobil one. I think the Mobil 1 has almost 3 times the pleated filter media that a fram does. Personal choice no right or wrong, but I won't filter coffee with a Fram filter.