Oil temp gauge/sender question

[Karls]

Hi ramva! I'd like to know... does the length of the wire going from
the gauge to the sender affect the reading? I think mine is showing
lower temps than it should. The gauge is a stock porsche 914 and the
sender is a VDO M14 x 1.5 located where the oil drain plug is supposed
to go.

TIA,
Karls

[Hal]

I had the same trouble when I used a drain plug sender on my beetle. It
never did register more than 120 degrees. Apparently the airflow across
the base of the engine prevents the sensor from giving a correct
indication. I switched to the dipstick sender and obtained more
believeable results(180-190 on a cool day, 210 on up for highway/hot
days).

Chris

[Joey Tribiani]

"Hal" <halat...@gmail.com> wrote in message
news:1144732485....@u72g2000cwu.googlegroups.com...

Chris, those readiings are right inline with my temp readings *with* the
drainplug sender....i have in the past had both bad guages and senders that
did not register correctly...even new ones...

[Packrat46]

What is the hottest temp that you have seen and still run. The reason is
that mine has been running between 250 and 280. It seems to be way to high
but I have never used an oil temp gage before. I use castrol 20-50w oil and
have used it in everything that I own since about 1973. It is supposed to be
able to take the heat and not break down like some other oils.

"Hal" <halat...@gmail.com> wrote in message
news:1144732485....@u72g2000cwu.googlegroups.com...

[Joey Tribiani]

"Packrat46" <philli...@verizon.net> wrote in message
news:ntS_f.11325$WL4.9074@trnddc07...

> What is the hottest temp that you have seen and still run. The reason is
> that mine has been running between 250 and 280. It seems to be way to high
> but I have never used an oil temp gage before. I use castrol 20-50w oil
> and have used it in everything that I own since about 1973. It is supposed
> to be able to take the heat and not break down like some other oils.
>
>

if your guage is accurate you should *never* see 280F....i say this because
if you by chance see the 250 you weren't paying attention and shutting it
down around 240-250 MAX

[veed...@isp.com]

Karls wrote:
> ... does the length of the wire going from
> the gauge to the sender affect the reading?

--------------------------------------------------------------------------------------------

Dear Karls,

The basic answer is 'no,' assuming the length in question is limited to
the distance from the engine to the dashboard in a bug or bus.

Prior to installing any instrument it's a good idea to verify that it
works and that it is reasonably accurate. With oil temp senders the
usual method is to provide proper electrical connections, such as
attaching a ground lead to a spare sump plate into which the VDO type
sensor is installed, and to then suspend the sump plate in a pan of
oil. A thermometer of known accuracy measures the temperature of the
oil as it is heated and the readings are compared to those on the VDO
gauge.

For the purpose of the test the sensor is connected to the gauge by
fifteen feet of wire, wound into a coil for ease of handling. For your
own information you may wish to insert a longer length of wire to give
you some idea of the potential difference in the readings. You will
find that for wire gauge of #16 or larger, there is no change even with
100 feet of wire.

However, you should also be aware of the fact that Volkswagen issued a
number of Service Notes with regard to the VDO instrument cluster
installed as an after-market item by many VW dealers, warning them that
the instruments did NOT accurately reflect the state of the engine.

With regard to the sump-mounted oil temp sensor readings, with the
vehicle in motion the temperature was about 100 degrees Fahrenheit LESS
than the core temperature of the oil in the sump, and as much as 150
degrees less than oil in the valve galleries. That's because the VDO
after-market sensor is in contact only with the relatively cool,
stagnant layer of oil under the strainer and the sensor is exposed to
the air flowing under the vehicle when in motion.

When required to provide a fully instrumented engine, Volkswagen
installed the oil temperature sensor at the inlet to the oil pump, thus
bathing the sensor in an active flow of oil drawn from the center of
the sump.

In the same vein, sensing cylinder heat temperature (CHT) with a
ring-type thermocouple installed under a spark plug also results in a
wide variation of temperatures from one engine to the next due to
variations in torque, the condition of the spark plug air seal and so
forth. When ACCURATE cylinder head temperture is required, as with the
later fuel-injection systems, Volkswagen provided a threaded lug
adjacent to the #1 exhaust stack. A Service Bulletin explained how to
fabricate a copper gasket with a similar lug, allowing early-model
heads to be used on the later-model, FI engines.

---------------------------------------------------------------------

When fitted with instruments, the oil temperature gauge on VW
industrial engines had no numerical markings. The gauge was divided
into three arcs: Green, yellow and red. As mentioned above, the
sensor was installed at the inlet to the oil pump.

By comparing the guage to a calibrated Stewart-Warner oil temp gauge I
found the green arc (ie, normal oil temp) went to about 220 degrees,
yellow to about 270 and red beyond that.

As a point of interest, the normal oil temperature of a 2180cc engine
installed in my 1965 bus is about 250*F. Given that the oil galleries
are running hotter than the temp measured at the pump, since compounded
motor oils (ie, 20W-50, etc.) begin to break down at about 300*F I
found it best to run straight-weight oil (ie, 30W for the cooler
months, 40W for hot weather).

(Regardless of your instrument readings, if you see varnish beginning
to build up in the valve gallery near your exhaust valves it's good
evidence that the temperature in that region [which is the hottest part
of your engine] is a above the break-down point of whatever oil you are
using.)

-Bob Hoover

[Packrat46]

Thanks Bob for the best info that I have ever seen on oil temp's and what to
watch out for. It was written so that I could understand what it was all
about.

<veed...@isp.com> wrote in message
news:1144859829....@t31g2000cwb.googlegroups.com...

[Karls]

Thanks a lot Bob, Your info has really cleared up my doubts.

I'll run some tests to see if everything is working well.

Thanks again, Karls

[Jim...@msn.com]

Hi!
Locating the sender at the sump drain plug hole will give lower temp
reading than what the oil temp is at the heads or at the cylinders.

I have a VDO cockpit oil temp gauge.
I use this special multiple adapter from CB Performance for my VDO oil
temp sender.

https://secure.cbperformance.com/catalog.asp?ProductID=837

The multiple adapter screws into the case where the dash oil pressure
warning light sender goes.

The oil temp sender and oil pressure switch sender screw into the
multiple adapter.

I get the same readings as when I used to use the VDO oil temp
dipstick.

I did not like having to always be extra careful with the oil temp
dipstick.

I measured the oil temp at the dipstick hole with an air conditioning
thermometer. It looks like a dial gauge with a metal stick on the
bottom.
When it read 180 degrees F, the VDO oil temp pointer was on the 1 at
the 180 degree F mark.
So I think my VDO oil temp gauge reads a little cooler than what the
oil temp really is.