What causes this excessive wear?

[RunninWild]

replaced the mc and booster and my brakes are soft on the first push then good on the 2nd. Almost sure its not air in the lines as I've bled over 1/2 a liter of fluid and I'm not getting any bubbles. Anyways back to the topic at hand.

I just went on my first real test drive since fixing the engine. I drove roughly 50km, the entire time my exhaust temp never went above 1100f, my coolant never went above 200f. At high rpm my oil pressure peaks around 45psi, cruising is around 30psi and at idle I saw it as low as 6psi but was at 10psi for about a minute when I parked it. I dont think my gauge is super accurate as its very sensitive to electrical load on my vehicle. If i turn on the head lights or heater or even my stereo up high my oil pressure reading drops, and coolant/egt increase. Assuming 10psi is accurate at hot idle measured from the head with 15-40w oil is this sufficient, or did the wear in my crank just destroy my new main bearings?

[ORCoaster]

Given the information about the lack of faith in the gauge I would say get a mechanical one on there instead and then provide those readings.  I wouldn't trust it at idle or anytime really. 

Reserving judgement until better/trusted information is provided.

[RunninWild]

Yeah I'll try and track one down. Is 10psi at hot idle sufficient though?

[air-cooled or diesel]

your electronic senders & gauges would seem to have a wiring issue, possibly getting power and mixing up power and signals from other gauges, or a bad spot to have gotten power from(if you ran a new, separate wire from fuse box), or possibly bad grounding, check senders have grounding, and gauge as well. i in most cases rely on an analog gauge(temporary), just dont go out and get a cheapie, hate them, metric. get reading then. 

[RunninWild]

I have a pretty fancy electronic multi gauge (madman ems1). Its wired into my cluster I think. The wiring in the truck is 30 years old and has too much resistance which is throwing the readings off. I'll install a relay and power the gauge dirctly from the battery. I do eventually plan on upgrading most of the wiring in the truck but for now it's what I have to work with. All the wiring to and from the sensors and the sensors themselves are new, it's just the power source for the gauge that is iffy.

The good news is an increase in resistance causes the reading to drop rather then raise. Which should mean the actual pressure should be higher then what the gauge displays. Like I said with it parked after a long drive and my headlights and practically all my electronics off it was idling at 10psi.

At what oil pressure when measured from the head is considered too low and the engine shouldn't be run? I know I'll need to pull the engine and rebuild the block in the future, I'm just trying to figure out what is considered safe to drive at and when I need to park it and start working on it again? I've read 10psi for every thousand rpm is good which is right about what my gauge is reading most of the time...

[RunninWild]

Bit of a new development. I drove another 120km on it yesterday. Oil pressure was pretty steady around 35-40psi while cruising on the highway. All of a sudden my gauge started going crazy jumping between 60-100psi multiple times a second. It did this for a few kms until I pulled over and let it idle a bit and the pressure dropped to 10psi. A few min later back on the highway it started doing it again. I got to my destination and parked for a few minutes and started it back up and oil pressure was normal again. On the return trip the gauge started going crazy on the highway again until it got to the point it was maxxed out at overrange (110psi) for the rest of the trip. When I was pulling into the gas station I noticed my gauge flashing check sender for a split second randomly for a few seconds.

Is it possible for the oil pressure to fluctuate super fast like that or is the sender most likely defective? Is it possible for it to even be pushing 110psi+ at operating temp pushing around 3500rpm?

[ORCoaster]

RunninWild,  Since you asked like 3-4 times and still didn't get an answer I ran downstairs to get the Bentley.

Table III  Tolerances, Wear Limits and Settings

F. Lubrication System
1 Oil Pressure
 A. Warning Light goes out (through 1981)  2.1-6.4 psi
     Warning Light goes out  (1982 Jetta)       26  +/- 3.0 psi
     Warning Light goes out (1982 and 1983 Rabbit and Pickup Truck and 1983 Jetta)  pressure below 2000 RPM     2.1-6-4 psi
 B. Normal Oil Pressure @2000 RPM with oil at 80 degrees C. (176 F)          28 psi

So it appears that 10 psi would be good at idle after a long run such as you describe. 

Now the problem I see is that you can't begin to trust that data point.  Not with the description you just gave of the 60- 100 psi bounce and then pegged at 110.  You may have one "pretty fancy multi-gauge" piece of crapola.  Or a very nasty connection at power or sender or ground or all three.

Is it possible for it to even be pushing 110 psi at operating temps at 3500 RPM you ask?

Well I hit that all the time at less RPM but it is in the morning within the first 3 miles of going to work.  I am waiting to pop an oil filter some day.  I think it is a result of a rebuild of an oil pump and I just put too much spring pressure against the relief in the pump.  Once I get the oil hot.  I run around 45 psi at 2000 RPM.  At idle it drops to 30 or 25 depending on how hot the oil gets.

So watching the pressure at idle is not a spec RPM.  Stop doing it.  2000 RPM is where you should be looking.  OK, now you need to fix some stuff.  Like I said, get MECHANICAL.  That is the way I go with all my add on gauges.   And I have plenty.  I do have some electronic temp readouts for the Veg Oil system.  Good to 185 F and until they get to 100 F they are to the tenth of a degree.  Very large blue or red numbers, 1 inch tall.

[RunninWild]

I think my readings are more related to my old wiring and I think my vdo oil sender is faulty. The truck is parked again for now. I will get the low pressure stock sensor installed and I'll see what I can do about finding some better gauges.

[air-cooled or diesel]

When I was pulling into the gas station I noticed my gauge flashing check sender for a split second randomly for a few seconds.

this is a concern, for one, if it is your dash idiot light flashing, you definitely have low oil pressure at that time, and possibly other time(s), this idiot has 2 senders, 1 for mains, 1 sender for head.
 
one thing im might point out, your fluctuations in your oil pressure readings(your current gauge) are most likely due to your faulty wiring &/or ground.
 

[RunninWild]

The engine isnt in a vw so I do not have the the oil pressure lights. My digital gauge was flashing check sender, which is something it typically does when a wire is disconnected or a sender is faulty. With the pressure being all over the map at a steady rpm, and the gauge errors I'm inclined to believe my sender is faulty.

Were your 1.6's you rebuilt turbo motors or n/a's? From what I've read turbos have less oil pressure, but I agree mine is probably a bit lower then optimal seeing as my crank had signs of wear and i didn't have it machined. I kind of cut corners on this as I wasnt able to pull the engine and have everything properly machined and put back together in a 100% clean and optimal setting. I'm planning on pulling the engine and completely rebuilding the bottom end, this was mainly meant to be a band-aid for the short term. Ideally I'll be able to get a year out of it and rebuild it next fall/winter.

I'm going to install a .5bar (7.25psi) oil pressure switch in the head and wire it up to a buzzer. Before my sender started going crazy I was having pretty decent pressure at higher rpm. I dont have a tach so I dont know exactly but cruise was around 30psi and high revs was around 45-50psi. Next weekend when I have some free time and with the new switch in the head I'll give the truck a good test drive 500ish km's. If it doesnt catastrophically fail and idle doesn't trip the buzzer I'm going to just consider it good until my idle pressure starts to drop and the buzzer sounds. I have a car I commute with so I wont be driving it all the time, it would just be nice to have a bit of peace of mind the thing isnt going to crap out at any moment.

Do cam bearings usually wear and effect oil pressure? Never even thought to have a look at them. Which bearing usually sees the most wear that would be worth having a look at?

[air-cooled or diesel]

as i was thinking and you have reaffirmed, your crankshaft. running those bearings like that, with low oil pressure, if not -0-oil pressure, for how long,, took metal (well some anyways) off crank. right now @10psi oil pressure isnt too close to dangerous,.

[RunninWild]

My trans is geared pretty small 5th gear at 100km/h is roughly 3275rpm, I usually cruise up to 120km/h at 3875rm and the fastest I've had it is 140km/h is about 4500 rpm.

Anyone familiar with the tdi oil pressure switches? partsplace lists it as .55-.85bar http://www.partsplaceinc.com/products/product-detail.aspx?keyword=VW+TDI+Oil+Pressure+Switch038-919-081&sku=17957 while it lists the 3 older style switches as a single rating. Does the range mean the sensor is only calibrated to somewhere between .55 and .85 bar? Maybe I'll just try something like this rated at 7psi https://www.summitracing.com/int/parts/crt-a68301/overview/

For that matter how much is the pressure difference between the filter flange and the head? Maybe the 1.4bar sensor hooked up as an idle pressure buzzer from the filter flange would be sufficient? Although 1.4 bar is probably fairly high for idle pressure even at the filter isnt it?

I'll also trying changing the oil and the filter again. I didnt change the filter when I did all the engine work so it might be a contributing factor, although it only has maybe 500km on it. Mann filter fyi

[air-cooled or diesel]

always change oil filter when changing out oil.

so whats the deal with your head, is it new? cam is it new? or the old one,lifters?

[RunninWild]

Head is original to the engine. I have a new head sitting under my bed though. Does wear in the heads usually contribute to low oil pressure on these engines? I did a bit of research last night and apparently these don't have cam bearings? Just the cam caps are line bored? How's that supposed to work without bearings?

I usually do change the filter with the oil. Only reason I didn't was because the filter was basically new...

[ORCoaster]

Cam works just fine without bearings.  Cam caps hold it nice and straight and materials are matched well enough that WITH PROPER OIL PRESSURE you don't get wear.  Ever see how much oil is pushed around up top with the engine running?  Makes a heck of a mess of the engine compartment in a hurry.