1.8T Oil Pressure Warning - Deceleration

[JKCutler3]

1.8t w/ 115,500 miles.

Ok, so let me start off by saying I'm an idiot. I changed my oil about 600 miles ago, used a Mann filter, however I grabbed 5w-30 synthetic, not 5w-40 like I meant to.

Today I drive about 100 miles highway and city and notice my check engine light come on. Ok, no big deal I'll check it when I get home (but i forgot my buddy is using my vag-com, perfect). About 10 miles later my Oil Pressure light comes on while coming to a stop at a light. I pull over, let the car sit, then limp her home stopping whenever the light comes on for a few minutes. I tried to keep the RMPs under 3k but still while slowing down the light would come on. A block away from my house no warning light on, I punch it to 5k, let off and sure enough around 2,200 the light comes on while decelerating, then goes away.

I've read a couple threads on the oil system and diagnosing the problem, which seems like it can be a lengthy and tedious effort that could yield no results. My previous oil change, I didn't find any metal in the oil so I'l hoping the bearings are still good.

I'm planing on changing my oil again to 5w-40 to see if that helps, however seems like there might be an underlying issue here.

Without knowing the code do you have any thoughts on issues, or next steps?

Personally, I'm thinking about putting her in the shop, but if I can avoid that I'd like to.

Thanks!

[MetalMan]

If it's the check engine light, then that's the first and most important thing to check. There's no sense in us flying blind.

Just want to double check, it's not the oil pressure light? Does the B6 have a separate oil pressure light?

[JKCutler3]

I have a check engine light, and also intermittent Oil Pressure Warning that comes up on the dash where mpg is displayed. Check engine is constant, oil pressure is intermittent. Ill have the codes tomorrow :/

[old guy]

Remove your oil filler cap at idle and see if it has excessive vacuum making it hard to remove. If it does, replace your PCV valve. A defective PCV valve can pull a lot of vacuum on the block under decell conditions. This coupled with the low oil pump output at low RPM's can cause the low oil pressure light to come on as you slow to a stop. If the light is coming on under low acceleration load that would be a totally different story.

[Chemmie]

You're not giving yourself much credit here. The owner's manual recommends both 30wt and 40wt oil. Viscosity isn't the cause of your problem.


Sent from my iPhone using Audizine

[MacFady]

Yes just forget about the oil, that has nothing to do with your problem.

[naysay15]

Put some seafoam in the oil and run it for a few miles then change it to some 0w40.

[Chemmie]

I have personally rebuilt an engine that still had seafoam in the crankcase. It thinned the oil to the extent the lifters made contact with their bores and a piston slapped around so hard it fractured a skirt. The only variable in this high-milage case was the addition of seafoam. It turns oil into a solvent- use it in your oil at your own peril.

As stated, your oil viscosity is not the problem.


Sent from my iPhone using Audizine

[blitz2190]

I have personally rebuilt an engine that still had seafoam in the crankcase. It thinned the oil to the extent the lifters moved in their bores and a piston slapped around so hard it fractured a skirt. The only variable in this high-milage case was the addition of seafoam. It turns oil into a solvent- use it in your oil at your own peril.

As stated, your oil viscosity is not the problem.


Sent from my iPhone using Audizine

well its only suppose to be used for like 20 miles if not less, anyone leaving it in there doesn't know what they doing. Its suppose to loosen sludge and build up so yeah it will be a solvent. To the OP do as old guy said and check for a bad pcv valve, but it also sounds like your oil pickup may be getting clogged, a boroscope would help here, you can get them pretty cheap now.

[Spike00513]

I have personally rebuilt an engine that still had seafoam in the crankcase. It thinned the oil to the extent the lifters made contact with their bores and a piston slapped around so hard it fractured a skirt. The only variable in this high-milage case was the addition of seafoam. It turns oil into a solvent- use it in your oil at your own peril.

As stated, your oil viscosity is not the problem.

Could this be why the owner's manual specifically states to use no oil additives? I don't know about Liqui-Moly Ventil Sauber or Jectron, but I think either Liqui-Moly or Motul was caught false-advertising some cleaner in a commercial, where all they did was smear a bunch of CV grease onto a good camshaft, and then wipe it off with a towel, to pretend it was a great success by the cleaner, for a visual impression sales tactic.
Not only that, but anyone with the most basic understanding of how an engine works, knows that cam lobe faces is one of the places such build-up would NOT occur, because it's got constant friction rubbing against lifters which is why it needs oil lubrication film in the first place.

Like that infamous Mk1 TT sludge picture, where the owner went 80k-mi without a single oil change. There was lots of sludge in the head, not the pistons where rings scrape the cylinder wall holding compression and combustion.

Maybe MMO/Marvel Mystery Oil is a gentler alternative? The only time I've ever used that was to try and prevent scoring when starting up an engine that was sitting still for a long time, by putting a teaspoon in each cylinder on top of the piston, to try and leak down past the rings and establish a lubricating film.
Maybe this was wrong, I don't know. Or overkill. Supposedly Group 4 PAO oil such as Motul 8100 X-cess 5w40, are polar and cling onto cylinder walls better for next startup or something.

Due to fear of hydrolock, I also rotated it by hand, and then cranked starter (without fuel) with open spark plug hole, to try and get out extra MMO and soak it up with towels.
Lots of white smoke.

well its only suppose to be used for like 20 miles if not less, anyone leaving it in there doesn't know what they doing. Its suppose to loosen sludge and build up so yeah it will be a solvent. To the OP do as old guy said and check for a bad pcv valve, but it also sounds like your oil pickup may be getting clogged, a boroscope would help here, you can get them pretty cheap now.

Well I ran it for up to 200 miles before an oil-change in another car but it's long-gone, so no idea how that worked out.
Which I think is what the bottle instructions say.
But the idea of loosening sludge to me is sketchy. Can't it break loose that stuff, to clog the pickup? Isn't the safer way a gradual clean with T6, 5k OCI, and maybe a pickup screen replacement or clean job?
I've heard of filling the crank with diesel for a few days (high cleaning power) before turning it over to get it flowing, then drain and some short interval low-weight oil changes, but I never tried it. Or the same thing with ATF. Or was it adding ATF? I forget.

Not sure what the best filter is, I've been using Mann 940/25.

[Chemmie]

well its only suppose to be used for like 20 miles if not less, anyone leaving it in there doesn't know what they doing.

The seafoam bottle itself states to leave it in for an entire oil change interval. In my case, it was added less than 60km to an otherwise decent running engine before it grenaded. Add it to a fuel system maybe but keep extraneous additives out of the engine oil.

Spike, your use of MMO was just fine in that case. You could have also used a relatively thin oil like 30wt to the same effect. Yes, some people use ATF due to the high detergent content (needs to keep all those hydraulic ports and galleries inside an auto trans sparkling clean).

[JKCutler3]

Remove your oil filler cap at idle and see if it has excessive vacuum making it hard to remove. If it does, replace your PCV valve. A defective PCV valve can pull a lot of vacuum on the block under decell conditions. This coupled with the low oil pump output at low RPM's can cause the low oil pressure light to come on as you slow to a stop. If the light is coming on under low acceleration load that would be a totally different story.

Nailed it! There is definitely excessive vacuum almost to the point where I thought the cap wasn't turned all the way. Still dont have my vag-com to check codes, but I'll start here. Thanks Old Guy!

[JKCutler3]

So its kind of hard to see through the intake manifold, but it looks like when you follow the bottom hose from the side of the intake manifold to the PCV, on the left side of the PCV there is a plastic piece that comes up from the direction of the oil filter. This piece is cracked and no longer connected to the block. Looks like there was a lot of oil build up and corrosion. Does anyone have any better pictures or part numbers for this?

Also it looks like the route of least resistance would be to remove the intake manifold.





I just pulled this off a video. Looks like its the 90 degree on the left leading up to the PCV.

[MacFady]

Sift through this thread and/or search for PCV in the search field for many other threads and pictures. There are some year to year differences in the B6 layout from what I remember from doing mine, there are also some other things to consider replacing at the same time while your there, and some that are prone to breaking while doing this repair. If you decide to remove the intake manifold to get better access (I'd recommend), don't forget a new gasket.

[JKCutler3]

So, as I was concerned about what ancillary parts may be needed I sent it to the shop for this repair. Here's the damage:

OEM PCV Valve - $37
OEM PCV Breather Hose - $48
OEM PCV Breather Hose (90 degree) - $75
(2.4) Hours Labor @ $115 - $276

w/Tax - $444

I'm a sucker for paying $275 for labor and a little extra for parts but its under warranty and I have piece of mind the job was done right...