[Vwdiesel] Risks of straight weight

[Shawn Wright]

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