Normal Oil Pressure??

[ftm1776]

1991 Jetta, MK2, non-turbo, 5 speed, 290,000 miles, original owner

I just installed a VDO oil pressure gauge, 0-80 psi range. I'd like to know if my readings are within the norm or not.
No work has ever been done to the block components, save for a cooling system rebuild, injection pump and injectors rebuild.
Head rebuilt after belt broke 10 years ago.
I have no idea what the pressures were when the car was new.

I'm running Delo 400 15W-40 oil; outside temp 60 degrees F.

Start up after warming engine with block heater, 75 psi

After reaching normal operating temp with temp gauge in the middle:
55 mph, 48 psi (in 5th gear)
35 mph, 20 psi (in 5th gear)
Idle, 10 psi

Oil consumption looks good to me. Maybe down 2-3 mm on the dipstick after 500 miles'

Comments, please.

[RustyCaddy]

Those pressure numbers are pretty close, a little lower mostly,  to what we get on a rebuilt CR motor with about 70,000 miles except the 35 mph is about 10-15 psi lower.

What your getting looks to okay.

[theman53]

Those are perfect numbers except you don't run 5th gear at 35mph. Not matter what trans you have that is lugging territory.

[ftm1776]

Those are perfect numbers except you don't run 5th gear at 35mph. Not matter what trans you have that is lugging territory.

Give me a little more on the "lugging" issue. 35 mph on flat ground, steady speed doen't feel like lugging, but I must plead ignorance on just what lugging does to hurt the engine. Educate, please.

[theman53]

Running the engine at or below 1,000 rpm in any gear is really hard on the bottom end. If you are coasting down hill it isn't bad, anytime you are maintaining speed or more than that, it is about the hardest thing on the rods and bottom end bearings. There is very little oil pressure to protect, as you see, at those rpm's. With an avx you would be around 1350rpm with an avn you would be at 1200rpm. I really don't see any mileage or any real benefit to shifting under 1500. I think all you are doing is stressing the bottom end, but it is your car you drive it as you see fit.

[ftm1776]

OK. Oil pressure !!! not enough to provide lubrication protection at lower rpm/load conditions.

Pretty obvious and "graphic" when there is a pressure gauge installed. I have never really thought much about oil pressure......23 years !!!

Thanks

[ORCoaster]

ftm1776,  Lugging an engine is going to cost you an engine rebuild.  I know I did that to my F150 thinking all the while, Man this is great for saving gas.  What a crock!  I had a 2.75 rear end and the overdrive transmission.  It really didn't turn much RPM at 45 at all.  So if I was in highway traffic and crusing along and the traffic would drop to 40 or 45 I would just keep it in OD. 

When things finally started to go wrong with the engine I took it to the mechanic, don't ask me why, and the first thing he did was drop the oil pan and one of the rod caps.  You guessed it.  Blue steel and worn all through and through.  He asked me my driving habits and I told him how I would just keep it in gear and let it eventually get back up to speed.   His advice:  STOP DOING THAT!   He said he would fix the mechanical part but it was up to me to keep it running after that. 

With the straight six 300 CID engine and the trans/rear end combo I had it did get good mileage at 65 mph but even the slightest hill, and there are many here on the coast I would have to drop it to 4th in order to keep speed steady and not have my foot to the floor.  In a gasser that is even worst than our diesels as it really scours the cylinders of most of the lubrication that I did have going.

So, why not run some RPMs?  These engines are really built for it and you are not giving up mileage, you are saving the engine.  DAS

[ftm1776]

OK, say pressures are on the low to marginal end of things. How should I approach investigating whether I need a rebuild at this time or plan for one in the near future.

Is there any need for further diagnosis?

What can be done by just dropping the oil pan??? I know the intermediate shaft bearings cannot be replaced this way.

Is it worth a piecemeal fix?

Is there anything that can be done between now and a complete rebuild??

I think you get my drift.....

Comments, please.

[ORCoaster]

If you drop the oil pan you can, A: remove the pump for cleaning, B: get any nasty junk and gunk off the screen so it gets a lot of oil rather than a little, C: check to see if the regulator pin is jammed up in some way with gunk and junk.  D: Check for loose pistons or worn crankshaft.  E: look up the cylinders to check for a gouge or wear line. F:  Clean the oil pan of stuff that doesn't drain out with the oil. 

Sounds like a doable to me.  Little time and big diagnostic payback.   

[ftm1776]

ORCoaster, Thanks !!!

What is the "regulator pin"? I cant' find it in Bentley's oil pump section. Maybe the "pressure relief valve" as shown in Bentley??

I might be able to remove the pan and oil pump for cleaning and a wear check.
I'm not sure I would know what to look for when it comes to gouges or wear line except for the obvious, but I could look.
Loose pistons or worn crank, I have to plead ignorance on making those judgements.

I don't yet have a reliable shop to make those diagnoses for me. If I had a trustworthy shop, I would probably turn the whole job over to them. It would be nice if I could just pay for good work and have good work done.......lots of pressure on the shops today!!!

If I do remove the pump, would there be any value in replacing it with a larger gear version?? i.e., could that buy some time before more serious repairs have to be affected??

[ORCoaster]

Sorry my terms were messed up.  Yes as stated in the Bentley, Pressure Relief Valve.

If I remember correctly, and that is a big IF, there are only two bolts that hold the oil pump up to the engine.  When you put it back be sure that the top of the shaft inserts correctly in the bottom of the vane or diaphragm vacuum pump or you will not get the pump up all the way and won't have brakes either. 

I wouldn't be replacing the oil pump unless it was worn out or not pumping,  You can hook the shaft to a drill and spin it and sink the pickup tube in a tub of oil to see what the performance is like.  Start slow to see if and where the oil will come spraying out.  It may be right at you.  Check that Bentley for routing of oil first.  This might be more of a mess than you want to deal with.  I have a spare pump buried in the shed under tons of other spare parts and I will try to dig it out today and look at it on the bench to see what is what on it.  My Bentley is buried as well so I may need to clean shop before I do anything. 

Keep us posted.

[ftm1776]

Let me be more specific in terms of my goal here: If I am headed for a rebuilt/re-manufactured engine, I would like  to put that off until the clock hits 300,000miles.

I may have been running with marginal pressure for a long time already but didn't realize it until I just recently installed the head pressure gauge.

Can any other work be done with the oil sump removed, besides cleaning and renewing the pump, that might boost oil pressure?? I know that's kind of like asking a proctologist to pull teeth !!!

[theman53]

Dakotakid posted a thread in the general a bit back. I think he was spot on. Low oil pressure on these engines are usually intermediate shaft bearing related. I have seen oil pumps that the shaft was almost worn off where the gear contacts and they still worked fine. If you pull the pan bearings are the thing I would look at most.

[Dakotakid]

As the oil pan comes off, make sure you put it in direct sunlight and look for "glit" before you wash it out with gas or whatever. Even if you don't get glit, that certainly does not mean you are out of the woods. It is just a preliminary step in the road to determining what is what.

The main bearing cap (lower bearing) will show crank wear. The upper rod bearing will show rod bearing wear.

Actually, if the pan comes off, and all the belts and pulleys are off, you should be able to remove the int. bearing cap and pull out the int. shaft enough to see some of the bearing......maybe not. Having the pan off would allow you to push up on the int. shaft for replacement into it's back bearing. You would have to replace both int. shaft seals (front and spaghetti strap) upon reassembly.

To me, 10 lbs at idle with hydro lifters does not sound adequate to activate those lifters.....esp. with almost 300,000 miles wear.

Do not try to rely on the "wiggle test" to determine front int. shaft bearing destruction. The shaft will not wiggle until massive damage is done. You will lose oil pressure LONG before the shaft wiggles like a big girl on the beach.

[ftm1776]

I can get some information by inspecting the bottom end with the oil pan off. Only a limited amount as I have no experience in such a diagnosis. An experienced mechanic would be able to tell a lot more, however, I can look at it and learn what I can by doing that.

Question: whether or not the oil pump is in good condition, will a new pump with 36 mm gears give me a temporary boost in pressure??
Or will the pump simply come up to pressure and bypass the excess oil back to the sump. I understand that the bigger pump is for the extra needs of the turbo engine.
I accept that a rebuild is in order, but would like to add a little to the pressure until I get a decent builder lined up (this is the tough part, not the money).

If replacing the pump is not a totally crazy idea I could pick one up and just replace the old with the new. Then, when rebuild time comes, the new pump will be in place and kept in the rebuilt engine. I probably would want a new pump in the rebuilt engine anyway, regardless of the size.

I really appreciate everyone taking the time to chime in here. Some of the information goes over my head and skill level, but is still helpful as I climb the learning curve on this project.