[Vwdiesel] Risks of straight weight

Val Christian val at mongobird.com
Tue Oct 11 11:47:11 EDT 2005


Remember that the VI of multivis oils will drop much faster than
with a straight weight.  Another strategy, if you are going to 
do very high temp runs, would be to use the 40W oil.  However, I 
would stay with the 30W during the initial breakin.  Again, I think
your high demands on the powerplant, and the  cooling and lubrication
subsystem, are such that you may be trading reliability for performance
to a ratio that many might find unacceptable.

FWIW, in aircraft, aircooled engines, we will see oil temps above
your experience.  

I don't have at hand he performance data on the oils you're discussing,
but the numbers seem reasonable.  Also, I'd have to check with our lube
people to see what the rating temps are.  Remember that viscosity is 
one parameter, lubricity is another.  I think you'll find that when 
viscosity improvers are a high percentage of the blend, that the lubricity 
is less than with a straight weight oil. 


> On 4 Oct 2005 at 6:44, Val Christian <val at mongobird.com> wrote:
> > There is some risk mitigation with cold WX starts using striaght weight
> > oil, because the residual oil in bearings has better lube properties than
> > a corresponding quantity of multivis oil.  Additionally, there will be more oil
> > regionally present, due to less "drain down."  Monitoring engine oil pressure,
> > and permitting temps to come up prior to applying load and also to increasing
> > engine RPMs, is another good risk mitigation strategy.
> <snip>
> Val,
> This is an interesting thread, and very relevant to me, since I took your advice and 
> ran 30W in my newly rebuilt 1.6TD Vanagon. I haven't caught up with all the mail yet, 
> but here is a quick report, along with a question:
> Trip was from Vancouver Island to Lake Chelan via Hwy 2 (Stevens Pass, ~4500') 
> then to Salmon Arm BC (mostly flat), then back over the Coqihalla Hwy to home 
> (several passes of >4000'). Total distance travelled was about 1700km, with average 
> fuel consumption of about 27.5 MPG US. Maximum oil temp seen was 265F at the 
> top of Stevens Pass, after sustained climbing in 4th gear with an EGT of 1200-
> 1400F. Coolant temp unknown, just over 3/4 gauge, so probably 230F+. Boost was 
> limited to ~11.5psi on this leg. Oil pressure was ~35psi @ 3000rpm when oil was 
> ~220F, but dropped to ~25psi @3000rpm when oil climbed over 240F (measured at 
> head). Hot idle oil pressure was from about 8psi to 15psi depending on temps. 
> During the trip, I increased boost by dialing in the BOV, so max boost was about 
> 15psi. I also advanced timing from 0.95 to 1.02mm. The latter seemed to reduce 
> EGT about 100F and improve power. I also reduced fuelling at the pump by perhaps 
> 1/4 turn in 3 steps until max EGT at WOT was ~1350F. Previously I could send the 
> EGT well past 1400F with little effort. Engine does not appear to smoke at all, even 
> under sustained WOT at any speed. Oil consumption was nil on the first 500km, after 
> which I broke the dipstick... (it was welded and brittle). All in all, a very good trip, if a 
> little nerve wracking at times. On the final leg, I drove most of the Coqihalla at 
> 110km, sometimes 120km/h, and lowest speed on the hills was 80km/h in 4th. Max 
> sustained engine speed was 4000rpm.
> Now to my question: it seems my hot oil pressure with 30W is lower than with 15w40. 
> I did some quick checking trying to figure this out, and found that the Viscosity at 
> 100C for 30W (Rotella, 10.9 cSt) is lower than for Rotella 15W40 (15.7 cSt), which is 
> to be expected I guess. But I was surprised that the 10w30 has a higher viscosity at 
> 100C of 11.9 cSt. Am I reading these numbers wrong? I would have expected the 
> 30W to be higher than the 10W30.
> Shawn Wright
> http://zuiko.sls.bc.ca/~swright
> '85 Jetta D 
> '88 Westy 1.6TD 5 speed
>  (see progress at http://members.shaw.ca/vwdiesels)
> '82 Diesel Westy
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