Cylinder wall scoring / Low oil pressure

[Benjamis]

Maybe scoring isn't the right word, but would you guys do anything about this?

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• Benjamis
• Jul 25, 2023

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• Benjamis
• Jul 25, 2023

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• Benjamis
• Jul 25, 2023

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• Benjamis
• Jul 25, 2023

I have a low oil pressure issue still after replacing the intermediate shaft bushings. Camshaft journal clearances are all below 0.002", as checked with an indicator not plastigage. Lifters and cam are brand new and the bores are all in the 1.378-1.379" range. I measured new lifters to be 1.376". Oil pump is in spec according to Bentley. No more oil leaks.

The oil light flashes a couple times on cold start, and I get the buzzer on hot days with hot engine between 2000-2500 rpm. I tested the sensors and they are good. The oil pressure gauge reads as low as 13psi at the head and 22psi at the oil cooler at 2k rpm, and about 8.5 at idle.

I'm looking to replace the rod and main bearings and rings. These marks on the cylinder wall aren't close to catching a fingernail but would you freshen them up somehow or not worry about it? I think the oil came from when I pulled off the head, but not totally sure.

 

[oilhammer]

Pull the pistons out, I bet they are not very nice.

I think that engine may need to be pulled out completely and properly overhauled or replaced.

 

[Benjamis]

Compression before removing the head was 385-405psi across the board. The car runs great, just have low oil pressure. Just put in a new clutch 10k ago. Not stoked about removing the block, I'm working on gravel not concrete, but do have access to a machine shop, and I guess as they say, do it once, do it right... Will pull the pistons shortly..

I don't guess anyone would condone doing some kind of deglazing with the block in the car, re-ring and go? Don't need a race care here. I'm a noob at engine rebuilding, be mean to me.

 

[Vince Waldon]

Lots of folks have had great success with an in-frame re-hone. It's a hone, not a bore, so it can't do much if the scoring is really bad or the cylinders are tapered... but for mild scratching it can be an OK way to extend the life of the engine.

All depends on how it measures up (and what the pistons look like) once you finish pulling it all apart.

 

[burpod]

i've done an in-block hone and engine overhaul in the gravel driveway (everything except the crank bearings which i wasn't worried about), with great success. it's not too bad engine ran fabulously for about 4-5k until my modified i-shaft snapped - but totally separate issue from the block overhaul.... you could check a crank bearing for a visual sanity check and save yourself from removing the whole thing + trans.

 

[thechoochlyman]

I just had something a bit similar happen to me last year. Been 15k miles and all good. lol

 

[burpod]

it would be a good opportunity to get some better pistons as those are likely the weak crappy ones. shouldn't be too hard to find a good used matching set of alh rod/pistons for a fair price.

 

[volksguy]

Plastic Gauge the Bearings clearance
Mains can be replaced with the crank installed
If to loose on the clearance 1 piece of newspaper on the bottom of a bearing shell is worth
1/2 of a Thousandths (old factory/machine's trick)
Possibly shim the oil pump spring to.

 

[Benjamis]

it would be a good opportunity to get some better pistons as those are likely the weak crappy ones. shouldn't be too hard to find a good used matching set of alh rod/pistons for a fair price.

Did all 1z's get the weak pistons or did they switch over at a certain point? My engine number is 921 977, which is after the switch to 7mm valves.

 

[Benjamis]

Well, truth be told, these pictures were from a couple months ago when I pulled the head due to suspect worn valve guides. The exhaust guides were close to out of spec so I replaced all the guides, then noticed many of my valves were out of round, so replaced those, then they say you have to replace the lifters if you replace the valves (AutohausAZ claims there is a TSB stating this and I heard elsewhere too but couldn't actually find the TSB), so I replaced those, and said the heck with it, I'll replace the cam while I'm at it. I replaced the intermediate shaft bushings as well due to 15 thou shaft play.

I was never one to replace things that aren't out of spec. But anyway, since I couldn't catch anything in the cylinder walls with a fingernail and wasn't sure what I was looking at due to inexperience, I put the head back on a month ago and drove it and it runs great but still low oil pressure. I was prepared today to pull the head again. I dropped the oil pan first and plastigaged the bearings. The rod bearings are all in spec, between the 0.051-0.076mm graduations on the plastigage scale. Wear limit is 0.08mm. I figure since I loosened the stretch bolts, I might as well replace the bearings, 2 have radial grooves scratched in where the oil hole is and all have minor pitting.

I checked the #2 and #4 main bearings. Clearance is less than the 0.051mm on my red plastigage. Wear limit is 0.17 and new is 0.03 to 0.08mm. So I don't think I will touch those.

I'm just not feeling hopeful that new rod bearings will fix my oil pressure issue. Can you lose oil pressure through the rings? Compression is well within spec. Not sure if I should bother pulling the head now and checking the pistons. Primary concern right now is oil pressure. Do I throw a new oil pump and/or turbo at it and hope the pressure goes up? Or are both my oil pressure sensors and my oil pressure gauge all wrong? Oil pump gear clearances are in spec according to Bentley. I tested the sensors according to a how-to somewhere on here and they checked out. What else could it be?

 

[Vince Waldon]

I'd not recommend throwing anything at it.

The rings are not part of the oil pressure gallery, so can't lose oil pressure due to worn rings.

There are no published specs for oil pressure at the head, but it is always much lower than at the cooler, and IMHO if you have pressure at all at the end of the head with a hot engine the head pressure is fine. 22 psi at 2000 RPM at the oil cooler is not really all that bad (10 psi per 1000 RPM is the usual rule of thumb)... assuming the engine was hot when tested. Hot as in "rad fans have cycled at least once)... per the Bentley.

You're right there... a rod bearing test or two will rule them in/out.

What oil viscosity are you running?

 

[Benjamis]

5w40 full synthetic. The oil pressure numbers are the lowest I have seen with fully hot engine on 90F+ summer days. But on those days, the oil pressure buzzer goes off over 2k rpm. Even on 80 degree days it goes off, that's not a good thing right? I was thinking the cylinder wall wear was from low oil pressure. I did overheat twice but caught it quickly, due to water pump failure and pulley belt failure. I thought I would try to fix this problem to avoid further cylinder damage, but also tempted at this point to run her til she blows.

 

[Vince Waldon]

If you're getting reasonable pressure via a gauge, oil nice and hot, but still the odd buzzer iust over 2000 RPM it might be worth shotgunning the pressure sensor... they are reasonably cheap and can drift out of calibration over time. Assuming the wiring to the sensor is ok etc etc.

I would NOT recommend shotgunning the sensor if you didn't already know your pressure is actually pretty OK.

 

[Benjamis]

Possibly shim the oil pump spring to.

To what extent, and what effect does it have? I don't remember seeing a spring in there, is it under the gears?

 

[Benjamis]

If you're getting reasonable pressure via a gauge, oil nice and hot, but still the odd buzzer iust over 2000 RPM it might be worth shotgunning the pressure sensor... they are reasonably cheap and can drift out of calibration over time. Assuming the wiring to the sensor is ok etc etc.

I would NOT recommend shotgunning the sensor if you didn't already know your pressure is actually pretty OK.

Yea I'll look into getting new sensors. I've been monitoring the pressure for over a year now. It hasn't gotten worse, but it's definitely higher in colder temps. But since spec is 29psi at the oil cooler at 2k rpm I thought the sensor was doing its job, but also it does say that oil temperature should be minimum 176F, which is not a very hot engine is it? I don't have an oil temp gauge but is it close to coolant temp?

It takes about 2 seconds after a cold start for pressure to register on the gauge. The oil light blinks 2 times before going out. If I take off right away it kind of lugs the first few times I hit the throttle, but after that rides like a dream. Not sure what to make of it all.

 

[Vince Waldon]

Normal for it to take several seconds after start-up to establish oil pressure.

Oil temp lags quite a ways behind coolant temp (oil has a lower specific heat, for starters), which is one of the reasons the Bentley defines hot oil as "rad fan has cycled at least once".... takes a while for the oil temp to catch up to the coolant temp. Have had Vdubs with gauges for both.

No real way to know actual oil temp without an oil temp sensor in an area of high flow... can't just tee to the oil pressure sender, as a tee is a dead end.

"Rad fan has cycled at least once" is probably as close as one can get to the right oil temp for measuring.

29 psi spec vs 22 psi measured.. might come down the accuracy of your specific gauge? Hard to say. Calibrated lab instrument or Harbour Freight special?

 

[Benjamis]

Harbor freight of course, why spend dollars on a good gauge when I can spend dollars on unneeded parts and days of labor in vain? Also I have never actually witnessed my radiator fans running. I just put in a new fan switch, and I have jumped the fans through the control module and the fans work. Coolant temp on the cluster is always around 190 but I understand it is not accurate. I have been wondering too if she runs too hot, that would sure lower the pressure. But on VCDS I have never seen coolant temp over 88C or so with fully hot engine, so I thought nothing more of it.

 

[thechoochlyman]

Did all 1z's get the weak pistons or did they switch over at a certain point? My engine number is 921 977, which is after the switch to 7mm valves.

They all had weak pistons. I don't recall if I gave any betters photos in my thread I linked previously, but all the pistons in my engine had the small oil drain holes and there wasn't a sleeved rod bearing. The new piston I ordered DID have the larger holes with the rod bearing. My engine came with 7mm valves as well.

 

[oilhammer]

I think "weak" is a relative term here.... I've seen plenty of 1Z engines that outlast the rest of the car. Mine had well over 300k and was still running fine, and that was with RC2.

But the ALH was a big improvement, not just because of the pistons.

 

[thechoochlyman]

Sure, for the most part they won't give you any trouble. If I hadn't pulled a B4V home over 350 miles up the steepest hill I could find I probably wouldn't have had any trouble either.

 

[Benjamis]

If I hadn't pulled a B4V home over 350 miles up the steepest hill I could find I probably wouldn't have had any trouble either.

Did you install a hitch on your B4?

 

[Benjamis]

Great news. A couple months ago I replaced the rod bearings and decided to forego re-removing the head and touching the pistons. Oil pressure has increased a few psi now. I'm looking at a minimum of 25 psi now on a 90+F day with hot engine. Quite often in cooler temps it's holding steady at 30psi. At 2k rpm of course, according to my harbor freight gauge. What I've really noticed is much higher oil pressure than before at higher rpms above 2k. I went ahead and put in a new oil pressure sensor at the filter flange too and haven't heard a chirp since. Got a few thousand miles on the 'new' engine and she's running like a dream.

 

[thechoochlyman]

Did you install a hitch on your B4?

Sure did, it was one of the last built by @TDIDaveNH . Nice and heavy with a 2" receiver.

 

[wonneber]

5w40 full synthetic. The oil pressure numbers are the lowest I have seen with fully hot engine on 90F+ summer days. But on those days, the oil pressure buzzer goes off over 2k rpm. Even on 80 degree days it goes off, that's not a good thing right? I was thinking the cylinder wall wear was from low oil pressure. I did overheat twice but caught it quickly, due to water pump failure and pulley belt failure. I thought I would try to fix this problem to avoid further cylinder damage, but also tempted at this point to run her til she blows.

Was it Diesel oil, not just Synthetic oil?
Also the API rating should be correct.
I did use Castrol (iIrc) Turbo Diesel oil for several oil changes.
Did not have any problems.

 

[Benjamis]

I usually buy Mobil 1 or Castrol Edge, or Quaker State, whatever is cheapest, as long as it says VW 502 00 / 505 00 and meets A3/B4, thought that was good, don't know fully what it all means. Pretty sure they all say they are for gasoline or diesel engines.

 

[Benjamis]

Sure did, it was one of the last built by @TDIDaveNH . Nice and heavy with a 2" receiver.

That's awesome. I remember reading the thread about those and being bummed that he sold them all years ago. You ever think of making some to sell?

 

[thechoochlyman]

That's awesome. I remember reading the thread about those and being bummed that he sold them all years ago. You ever think of making some to sell?

I'm not really much of a fabricator, just a machinist. lol Plus there's probably very little demand for them nowadays. I think he mentioned something about still having a copy of the prints, maybe he'd be willing to share so you could take it to a fab shop?

 

[Benjamis]

Hmm, good idea. I guess it's time to try my hand at welding.