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Discussion Starter · #1 ·
Hi all, I have been running Castrol 20w50 since we bought the car in 2016 and I am thinking of switching to Shell Rotella T4 15w40. I notice on cold starts the car runs a little rough and we seem to get smoke out of the tailpipe that we didn't have for the first few years. After it warms up for 2 minutes and the oil begins to circulate everything runs like a top. We originally ran the 20w50 to prevent the oil light from flashing but it still does it. We've put on approx. 2000 miles since we bought it and the car mostly sees trips to the farmers market or ice cream shop on sunny days.


I am wondering if the car doesn't like the 20w50 oil. We only run the car in 40F temps and above but I am tempted to try a slightly lighter oil to see how it performs.


Curious on peoples thoughts about making the move and anything else we should be looking into? Thanks.
 

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what filter you using?

Bad ones that cause a intermittent flashy light:
Bosch
Fram
Store Brand/Generic.

Ones that don't:
Wix
NapaGold (wix)
PurelatorGold
Mobile1
Mann
Mahl
Genuine VW.

Have you verified your oil pressure with a Mechanical Gauge?
 
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Discussion Starter · #3 ·
what filter you using?

Bad ones that cause a intermittent flashy light:
Bosch
Fram
Store Brand/Generic.

Ones that don't:
Wix
NapaGold (wix)
PurelatorGold
Mobile1
Mann
Mahl
Genuine VW.

Have you verified your oil pressure with a Mechanical Gauge?
Brian, we have only been using VW filters from the dealer. The gauge has read 5 bar since we got it in 2016. I am not certain if it is a gauge or sensor issue but it's definitely not running at 5 bar. If I recall I replaced the sensor on top of the oil filter housing a few years ago.

We have not verified with a mechanical gauge.
 

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The oil pressure sender is a Can shaped that has 2 electrical connections, and is located on the side of the HEAD (right) it is about 60 bucks don't go cheap, and the thing measures low pressure at idle, and Oil pressure to the pressure gauge. The ones on the Oil Filter flange are oil Temp (black) and Low pressure high RPM (white).

I run 20w50 year round in my cabriolets but then I live in the south. Up north I used to run 20w50 for the summer and 10 or 15w40 for the winter.
When I had a rabbit diesel in the north or south I ran 10w30CC/CD with a wix filter.

Bad grounds can cause the voltage from the senders to be reduced, so if you haven't changed the grounds from the Battery to the frame and frame to the engine/tranny you may want to do so.
 

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Discussion Starter · #5 ·
I've cleaned the sensor (although it looked clean) and put new connectors on the wire ends. I think the previous owner replaced it because it is shiny clean compared to the rest of the engine compartment. I will do the battery grounds next as I have not replaced them yet.

Although I must note the oil light only flashes at idle and not all the time, and only certain times but the gauge will always read 5 bar. Before we replaced the fuel pumps this spring it flashed all the time unless driving above 50mph.
 

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Sounds like a sender issue.... If the POS replaced it with a Generic or EBAY variety, that is what will happen seen it personally, so I sucked up and bought the 60 dollar one from mk1autohaus and problem went away...
 

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Discussion Starter · #7 ·
Would the sender be the cause of the smoke though?

I should also note, more smoke began happening after we replaced the fuel pumps even though the oil light flashes less since their replacement. We run premium fuel in the car as the previous owner installed an exhaust header He said it needs premium now due to the header, not sure why this is. I am curious if the premium fuel is maybe an issue if it's not burning correctly?
 

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Would the sender be the cause of the smoke though?

I should also note, more smoke began happening after we replaced the fuel pumps even though the oil light flashes less since their replacement. We run premium fuel in the car as the previous owner installed an exhaust header He said it needs premium now due to the header, not sure why this is. I am curious if the premium fuel is maybe an issue if it's not burning correctly?
I have personally installed a header on my 90 Cabby, and had no issues with running 87 Octane in it with smoking more than the normal evaporation of water out of the exhaust at start, Installed it because of the Poor re-design of the Exhaust Manifold that every Cabriolet (90's) I owned had the manifold that was Cracked/Cracking.....

I would be looking at the Valve train seals and or Ring wear if you are burning oil (blueish Smoke). While the higher octane will burn more evenly and completely for increased HP/Mileage I don't think it to be an issue on well maintained and properly timed rides.

I have been running 20W50 in my Cabriolets for over 15 years and had no issues. I have seen more issues with the blinky oil light at idle caused by Crappy filters rather than oil vis. I should also state that I replaced most of the oil pumps with that off a 2.0L VW as the gearing went from 30-32mm to 36 and provided me with more oil flow.... In doing the swap over I had to use the Pick-up Tube from my 1.8L pump as it is Shorter than the 2.0 and led to the Pan not being able to be installed, on earlier 1.8's you may need to use longer bolts for the pump to engine, but on my 90's it was a non issue as the 90 used longer bolts. But the Pickup tube change over was required.... If you go that route as well you should buy a new windage tray for the pump as I broke a finger or two off of mine removing it, but once learned I had a spare on hand for the next one but never needed it...
 

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15W40 is the correct oil for the engine. Our VOA Regional Tech Rep brought us a Tech Bulletin about using 20W50 - this was 1986 or 87.
According to VOA, the extra film thickness of 20W50 was found to increase clearances and reduce oil pressure over a relatively short time. 50,000 miles as I recall.
If the owner used 20W50, then you are probably stuck with the wrong oil. It confuses the low oil pressure warning system - VW was pretty adamant about their 15W40.
If you can use 15W40, Rotella is a great solution. It's a diesel formulation, so it has higher lead/phosphorus content, which is better for your vave train. I'd try Rotella, or Valvoline 15W40 Diesel and see if you still smoke.
 
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