[T3] Engine oil temp?

[William Jahn]

I'm using Valvoline SAE 40 racing oil. I could go down to 30 yet since I
don't know the bearing clearance I use the 40 and never had any issues with
it. As far as the gauges I replaced them mainly because they were so old
and now the readings are at least closer to real than before. I temp sensor
in in the sump. I mainly use the gauges as a base to see if anything
suddenly alters like a higher or lower pressure or temp just a guide.

 Still I want to at least see what the relief and control valves look like
just to rule them out as a possible issue . I imagine over many years the
springs through heat have weakened somewhat yet don't plan to change them ,
it's only to know if either valve might be sticking and I have two NOS
valves if needed. I did replace the pressure relief when I rebuilt this
engine mainly because it had a few light scuff marks. The bores looked fine
in the case. Based on 23 years since I had them out.

 Many go by pulling and seeing if they can hold the dipstick to tell if an
engine is running too hot. The temp sensor in the sump would basically read
what the stick does yet this seems more true on type 1 engines as far as I
can tell . If I place the sensor in the relief valve it may read closer at
least I think so and only because it's out of the oil flow and the oil has
to travel from the sump through the pump  then passages to the bearings
reading the oil temp closest to the cooler  and it's out of the air flow.
Reading the temp after the cooler would be better yet that's not possible
yet the sump is after the cooler. I thought of using both sensors with a
switch before the gauge yet that to me seems like overkill. For now If I
want it's easy enough just to connect the same 1/4" female spade to one
then the other since it will reach either location just to see if one might
be the better location. I would choose the sensor that reads higher. This
is by no means  a scientific approach . What it is is based on a few sites
that tried both locations yet on a type 1 and stated the relief valve
location read the same as a calibrated thermometer in the dipstick tube
where in the sump was a much cooler reading. It does not make much sense to
me yet it did for them. If I recall this was based on the air flow as well
as the fact that heat rises. I can't say what effect  exhaust heat enters
the equation. Since a stock muffler has heat shields and I don't have the
stock unit my header is no where near either location.

On Sat, Jul 18, 2020 at 9:40 AM Jim Adney <jadney at vwtype3.org> wrote:

> On 18 Jul 2020 at 7:44, William Jahn wrote:
>
> > I replaced the oil pressure  and temp gauges and so far the oil pressure
> > sender. It's mounted on a square profile steel elbow to the cooler with a
> > banjo fitting , don't recall if that came on my engine.
>
> That banjo adaptor came from earlier dual carb engines. It was necessary
> to
> clear the dual carb air cleaner. That location is fine for oil pressure,
> but it's
> no good for temp, because there won't be any flow past the sensor in that
> space.
>
> Your other post indicates that you're measuring oil temp either at the
> sump
> or at one of the relief valves. Either location will be fine.
>
> >  Here's the deal . The oil pressure readings are a little higher than the
> > 10 pSI per 1,000 rpm rule. I don't know who made the rule but I do know
> VDO
> > gauges are not 100% accurate at least to say they may not be.
> >
> >  7 mile drive 81 * idle PSI 25 . Oil temp read 180* . Shut it down for an
> > hour temp dropped to 140 oil pressure back up to 35 pSI 1,000 RPM the
> > highest it gets @180 * 40 PSI. Drove home 7 miles ambient 85*. read about
> > the same. Shut it down for 10 minutes oil temp was 190* .
> >
> >  The temp will rise yet it almost seems as if the cooler always has oil
> > flow.
>
> The cooler will always have oil in it, regardless of whether there is
> significant
> flow or not. There may be an air bubble at the top, where the pressure
> switch/gauge is, but that won't affect the pressure reading. It would
> affect a
> temp reading if your temp sensor was there.
>
> If you're running heavier oil than VW specified, the pressure relief
> passages
> can be overwhelmed. This may be why you see pressures above 28 psi,
> which is where the relief valves are supposed to regulate. It may seem
> counterintuitive, but high oil pressures are not necessarily good. What
> you
> need are sufficient oil volume delivery to the bearings.
>
> Journal bearing lubrication is not an obvious thing. The rotation of the
> shaft
> forces oil into areas where the shaft has moved closer to the bearing,
> creating high pressure areas where high pressure is needed. It's important
> for oil to be introduced only into low pressure areas, which is why the
> oil
> entry points in a bearing may seem odd. They are carefully planned.
>
> The oil pressure in the high pressure areas of the bearing will be MUCH
> higher than what's available at the entry point. This is called
> hydrodynamic
> lubrication. To understand this, draw yourself a sketch of an off-center
> shaft
> rotating in a bearing. Note how the rotation will push oil into the wedge
> area
> where the shaft is starting to get close to the bearing. The closer the
> shaft
> gets to the bearing, the higher the oil pressure will be at that point,
> and it has
> little to do with the oil pressure at the entry point.
>
> So, it all gets back to the fact that what you need from your oil pump and
> relief valve is high oil delivery volume, not necessarily high oil
> pressure. In
> their late engines, VW increased flow by enlarging the oil pump gears and
> reduced the need for high pressure at the pump by increasing the size of
> the
> oil passages, thus reducing pressure drop in the oil passages. The larger
> oil
> passages were especially useful in cold weather, when the oil was much
> thicker.
>
> I don't see any problem with the temps and pressures you posted, but be
> aware that all commercially available gauges tend to be pretty inaccurate.
>
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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