Which oil? [emoji12]

Discussion in 'Mech Tech' started by SkutterBob, Mar 22, 2020.

  1. Ok, this isn't an ask about which oil I should use, more of what I have discovered over 6 years of Bay window ownership. It may help someone with their choice of oil and real world difference between different grades and how they ran.

    My bus engine is a type 1 1641 with twin ICT34 carbs and a custom stainless exhaust. So a little tuned but not seriously. One thing that does happen is that the tappet noise is amplified by the exhaust silencer and can be quite loud when they need adjusting. I also noticed that different grades of oil affect it as well so here are my findings.

    None of these affected my normal running engine temperature and tappets were adjusted properly at time of observation.

    Oil grade: 15w 40
    This oil is thin on cold cranking so starting is easier. Engine power is slightly increased as there is less drag but it made sound like a bag of nails. I could hear quite obvious tappet noise and it did not sound good. Once up to temperature all was fine.

    Oil grade: 20w 50
    Much thicker oil and recommended by VW Cool Air. Noticeable slow down cranking speed especially on cold days. Slight loss of engine power as more drag when warm but overall quieter engine. Very little tappet noise.

    Oil grade SAE30
    This was picked up accidentally by Mrs Skutterbob and is recommended by VeeWee (part of GSF) in Norwich. This is a single grade oil so there is no difference between cold and hot viscosity. I needed to do an oil change so used it and was pleasantly surprised. Cold cranking is a bit slow but once the engine warms up it runs quite nicely and had more power than the 20w 50 because it is thinner. Tappet noise was the quietest of all when cold. This oil seemed to be the best of both worlds for my VW, protection for cold starting, but not too thick whilst running to show a loss of power.

    Here is a good guide on what the oil grades mean

    Last edited: Mar 22, 2020
  2. I think that's a pretty good explanation of oil grades, well at least the second number is. I find though that the first W figure is given using imperial units whereas the second is in metric. If it was in metric like the second number, 20W would be more like 500. Why is this? Anybody?
  3. I found my engine ran cooler with 15/40 than 20/50 I think it was because the oil pressure on 20/50 was close to the bypass valve operation pressure.
  4. I didn't really see a difference but I can see why it might. Used to run a mini on 20/50 and it was like driving in treacle, so not a big fan of it.
  5. OK this is slightly wrong. The W number is in Poise and the other number is in centiStokes. Both are metric units. One measures dynamic viscosity and the other kinetic viscosity but I'm none the wiser why they're different.
  6. I used to use 30s. Most of it ended up on the drive!
    Gingerbus and SkutterBob like this.
  7. Apparently the chemical missing in modern oil is zinc, zddp.
    This helps cams, followers.
    Keith seume reconned a race car on synthetic would need half as many rebuilds.
    Find an oil with both. It won't be cheap, but neither are air-cooled engines today.
    SAE30 works best at one temperature. 10/60 all.
    SkutterBob likes this.
  8. Porsche know a fair bit about air-cooled engines. They have had two oils engineered for classic Porsches (Inc type 4 vw).
    Don't ask if it's cheap but it has a nice tin for shelves. Anyway if you can find something similar specs at less money you're a winner. Remember a second hand Porsche engine costs £10k, so Im sure they want some quality.
    Some Porsche people used Mobil syn Motorsports 15/50. Superseded by 10/60. Fully syn of course.
    Some American oil companies do stuff for older v8s that says race only. Probably because It has zinc in it for older engines and if you put it in newer cars the catalyst fails.
    Mark Darby and Surfari like this.