VDO head temp in a bus

Now that I've done some research here on ow the VDO cylinder head temp
gauge works I wonder if I did a bad thing.
I have a 1971 Bay window bus with a sunroof and that means it has a
belly pan which makes it almost impossible to run wires along the
frame, so I have run all of them inside the interior down the left side
and of course that left me about three feet short on the supplied lead
length for the gauge.
Thinking I was doing an ok thing I just spliced the needed length and
checked polarity and hooked it up to the gauge.
Then I found it too difficult to reach into the #3 plug hole so I
attatced the sensor to the intake bolt, well that spot is of little use
I now know but the gauge needle never moved at all.
Thanks for your input.

"Volksrod" > wrote in message
oups.com...
>
> Now that I've done some research here on ow the VDO cylinder head temp
> gauge works I wonder if I did a bad thing.
> I have a 1971 Bay window bus with a sunroof and that means it has a
> belly pan which makes it almost impossible to run wires along the
> frame, so I have run all of them inside the interior down the left side
> and of course that left me about three feet short on the supplied lead
> length for the gauge.
> Thinking I was doing an ok thing I just spliced the needed length and
> checked polarity and hooked it up to the gauge.
> Then I found it too difficult to reach into the #3 plug hole so I
> attatced the sensor to the intake bolt, well that spot is of little use
> I now know but the gauge needle never moved at all.
> Thanks for your input.
>
>

........The wire from the gauge to the connection with the sensor lead can be
lengthened I would think. The voltage is low enough so that it shouldn't
matter. The intake bolt location for the sensor is no good though. Under the
#3 spark plug is where you need to put it. Just bend it so the ring shaped
part is at an angle with the shank portion so that it'll fit down under the
plug.

.......I don't have much faith in mine. For a long time, I thought that my
head temps were way too high until I checked with an IR temp gauge and
discovered that the VDO was reading between 75 and 100 degrees F. too high
in the 350+ range. Oddly enough, the IR gauge and the VDO agreed at 250 deg.
You'd think that VDO would have calibrated them at about 400 instead of 250.

Yeah...they're an odd device to say the least...Actually because it's a
'thermal coupling' device..the temps vary with the ambient
temp..opposite of what you'd think...most are 'zeroed' for proper temp
at 68F....anything lower..and it appears to be running hotter...higher
ambient temp makes it appear cooler!!..Very strange...wish they could
develop a more precise, economical gauge. Pat
Tim Rogers wrote:
> "Volksrod" > wrote in message
> oups.com...
> >
> > Now that I've done some research here on ow the VDO cylinder head temp
> > gauge works I wonder if I did a bad thing.
> > I have a 1971 Bay window bus with a sunroof and that means it has a
> > belly pan which makes it almost impossible to run wires along the
> > frame, so I have run all of them inside the interior down the left side
> > and of course that left me about three feet short on the supplied lead
> > length for the gauge.
> > Thinking I was doing an ok thing I just spliced the needed length and
> > checked polarity and hooked it up to the gauge.
> > Then I found it too difficult to reach into the #3 plug hole so I
> > attatced the sensor to the intake bolt, well that spot is of little use
> > I now know but the gauge needle never moved at all.
> > Thanks for your input.
> >
> >
>
> .......The wire from the gauge to the connection with the sensor lead can be
> lengthened I would think. The voltage is low enough so that it shouldn't
> matter. The intake bolt location for the sensor is no good though. Under the
> #3 spark plug is where you need to put it. Just bend it so the ring shaped
> part is at an angle with the shank portion so that it'll fit down under the
> plug.
>
> ......I don't have much faith in mine. For a long time, I thought that my
> head temps were way too high until I checked with an IR temp gauge and
> discovered that the VDO was reading between 75 and 100 degrees F. too high
> in the 350+ range. Oddly enough, the IR gauge and the VDO agreed at 250 deg.
> You'd think that VDO would have calibrated them at about 400 instead of 250.

"pat" > wrote in
oups.com:

> Yeah...they're an odd device to say the least...Actually because it's
> a 'thermal coupling' device..the temps vary with the ambient
> temp..opposite of what you'd think...most are 'zeroed' for proper temp
> at 68F....anything lower..and it appears to be running hotter...higher
> ambient temp makes it appear cooler!!..Very strange...wish they could
> develop a more precise, economical gauge. Pat
> Tim Rogers wrote:
>> "Volksrod" > wrote in message
>> oups.com...
>> >
>> > Now that I've done some research here on ow the VDO cylinder head
>> > temp gauge works I wonder if I did a bad thing.
>> > I have a 1971 Bay window bus with a sunroof and that means it has a
>> > belly pan which makes it almost impossible to run wires along the
>> > frame, so I have run all of them inside the interior down the left
>> > side and of course that left me about three feet short on the
>> > supplied lead length for the gauge.
>> > Thinking I was doing an ok thing I just spliced the needed length
>> > and checked polarity and hooked it up to the gauge.
>> > Then I found it too difficult to reach into the #3 plug hole so I
>> > attatced the sensor to the intake bolt, well that spot is of little
>> > use I now know but the gauge needle never moved at all.
>> > Thanks for your input.
>> >
>> >
>>
>> .......The wire from the gauge to the connection with the sensor lead
>> can be lengthened I would think. The voltage is low enough so that it
>> shouldn't matter. The intake bolt location for the sensor is no good
>> though. Under the #3 spark plug is where you need to put it. Just
>> bend it so the ring shaped part is at an angle with the shank portion
>> so that it'll fit down under the plug.
>>
>> ......I don't have much faith in mine. For a long time, I thought
>> that my head temps were way too high until I checked with an IR temp
>> gauge and discovered that the VDO was reading between 75 and 100
>> degrees F. too high in the 350+ range. Oddly enough, the IR gauge and
>> the VDO agreed at 250 deg. You'd think that VDO would have calibrated
>> them at about 400 instead of 250.
>
>

They're just a novelty item unless you run either a dually on a centrally
located head bolt on each head, or a quad, preferably using the sparkplug
sensors. When I bought my quad, it was about the same price as two VDO
singles, but came with 48" stainless steel wrapped leads. With the quad
gauge, you can, at a glance, see if any cylinder is out of range of the
others. Ambient temp doesn't matter because it affects all 4 equally and
the actual numbers mean little to nothing. Typical of my '79 bus, #1&#3
would start out higher and the temp rise would be quicker than #2&#4.
Once up to operating range and pulling hard, they would all fall exactly
in line with each other. Cooling down went the same way. I actually honed
#3 cylinder an extra thousandth and it ran very close to #1. Prior to
that, it ran 50 degrees hotter all the time.

Before the quad gauge, I ran two VDO senders: one on #1 & one on #3. I
had a single gauge and used a toggle switch. I usually monitored #3. With
a brand new motor, it was #2 that the injector backed out from and seized
up. If I had been running a dual gauge I might have seen the right side
running hotter. With the quad gauge I definitely would have seen it.

I highly recommend the quad CHT gauges. For FI engines, a CB mixture
gauge with the oxy sensor in the #3 header runner (between the exhaust
port and the heat exchanger) along with a quad CHT gauge will tell you
everything you nedd to know to actually save your engine as they will
indicate what is going wrong in time to avoid calamity, if you're paying
any kind of attention. I was always anti- oil temp gauge, but have since
figured out that the actual failure of my last T4 motor would have been
indicated by an oil temp gauge but was not caught by the CHT / Mix combo.
The failure was in the bottom end (where T4's are never supposed to
fail!) When the oil temp started to go out of normal range, I would have
consulted the CHT and Mix gauges and determined that I had either a main
bearing or rod bearing heating up. I probably could not have saved it at
that time, but would have at least had something rebuildable!

Put your single VDO gauge in a pan of water on the stove. Watch the
needle on the gauge rise as the water reaches boiling. Now point a hair
dryer at the connector end of the sensor wire (not the sensor end which
is in the water!) As you heat the connector end, the reading on the gauge
drops. When in actual use, if your running on hot blacktop and your
engine is running hotter than it should, it is very likely that your
single VDO CHT gauge will have a reading lower than normal.

With the 48" leads on the Westach Quad gauge (from Aircraft Spruce) I was
able to put the connector ends on top of my tranny. I also placed a
sensor for a thermometer there. The Westach gauge is calibrated for a 75
degree cabin temperature. That means that when the connectors were at 75
degrees, the gauge was calibrated to read correctly. If the temp on top
of the tranny was 100 degrees, the gauge would read 25 degrees lower than
actual temp. If the temp on top of the tranny was 50 degrees, the reading
would be 25 degrees higher than actual. The only times it was drastically
beyond the range of +/- 25 was when parked. In summer, the tranny case
absorbed heat from the engine and at times the top of the tranny was over
200 degrees when not moving. Likewise, in winter, I saw the thermometer
in the teens more than once, but once underway, it warmed up to the 50/60
range and likewise in summer, cooled to the 70/80 range.

The important thing to remember is that all four readings are affected
equally. You still look for one running out-of-range. Besides that, where
I drive, the ambient temp is almost never above 80 or below 50 for very
long at a time. It was interesting to see the actual temp trends, but of
absolutely no value in monitoring safe engine operation. Freeway
operation saw temps rise and fall more than 200 degrees in half a mile as
hills were climbed and crested.

As important as the proper gauges is the ability to make on-the-fly
adjustments. Adding a slide-type adjustable resistor to the FI CHT sensor
enabled me to enrichen the mixture as temps increased and when hard pulls
were encountered. It also enabled speeds of over 100mph - coupled with a
dashboard mounted momentary switch wired into the cold start injector, it
enabled reaching that speed rather quickly!

(Not as quickly or smoothly or effortlessly as the Subey though!)

--
-BaH
Dave Pearson
79 Bus w/ Subey 2.2
74 Bus Project

Here is an interesting write-up on VDO gauges. Scroll down to the cyl head temp section:
http://www.ratwell.com/technical/VDOGauges.html


"Tim Rogers" > wrote in message ...
> "Volksrod" > wrote in message
> oups.com...
> >
> > Now that I've done some research here on ow the VDO cylinder head temp
> > gauge works I wonder if I did a bad thing.
> > I have a 1971 Bay window bus with a sunroof and that means it has a
> > belly pan which makes it almost impossible to run wires along the
> > frame, so I have run all of them inside the interior down the left side
> > and of course that left me about three feet short on the supplied lead
> > length for the gauge.
> > Thinking I was doing an ok thing I just spliced the needed length and
> > checked polarity and hooked it up to the gauge.
> > Then I found it too difficult to reach into the #3 plug hole so I
> > attatced the sensor to the intake bolt, well that spot is of little use
> > I now know but the gauge needle never moved at all.
> > Thanks for your input.
> >
> >
>
> .......The wire from the gauge to the connection with the sensor lead can be
> lengthened I would think. The voltage is low enough so that it shouldn't
> matter. The intake bolt location for the sensor is no good though. Under the
> #3 spark plug is where you need to put it. Just bend it so the ring shaped
> part is at an angle with the shank portion so that it'll fit down under the
> plug.
>
> ......I don't have much faith in mine. For a long time, I thought that my
> head temps were way too high until I checked with an IR temp gauge and
> discovered that the VDO was reading between 75 and 100 degrees F. too high
> in the 350+ range. Oddly enough, the IR gauge and the VDO agreed at 250 deg.
> You'd think that VDO would have calibrated them at about 400 instead of 250.
>
>

"Karl" > wrote in message
m...
>
> Here is an interesting write-up on VDO gauges. Scroll down to the cyl head
temp section:
> http://www.ratwell.com/technical/VDOGauges.html
>
>

.......Thanks for that link Karl. I'm going to buy one of those Dakota
Digital head temp gauges.

"Tim Rogers" > wrote in message
...
> "Karl" > wrote in message
> m...
> >
> > Here is an interesting write-up on VDO gauges. Scroll down to the cyl
head
> temp section:
> > http://www.ratwell.com/technical/VDOGauges.html
> >
> >
>
> ......Thanks for that link Karl. I'm going to buy one of those Dakota
> Digital head temp gauges.
>
>

...........I just placed my order today. They have a special sensor lead for
acvws that is 18 feet long and has the correct 14mm ring for sitting under
the spark plug. Its number is SEN-11-8 but doesn't come up on their website
so I had to place my order over the telephone. My total expense is about
$160 which includes about $25 for 2nd day UPS from South Dakota to NY.

........It's going to be great to have an accurate cylinder head temp at last
to look at while driving.

Thanks to all for your input.
I will try hooking up the CHT gauge again today.
As advised I will use them for trend rather than actual.
Plus they do fill up an unsightly hole the PO left in the dash.

"Tim Rogers" > wrote in
:

> "Tim Rogers" > wrote in message
> ...
>> "Karl" > wrote in message
>> m...
>> >
>> > Here is an interesting write-up on VDO gauges. Scroll down to the
>> > cyl
> head
>> temp section:
>> > http://www.ratwell.com/technical/VDOGauges.html
>> >
>> >
>>
>> ......Thanks for that link Karl. I'm going to buy one of those Dakota
>> Digital head temp gauges.
>>
>>
>
> ..........I just placed my order today. They have a special sensor
> lead for acvws that is 18 feet long and has the correct 14mm ring for
> sitting under the spark plug. Its number is SEN-11-8 but doesn't come
> up on their website so I had to place my order over the telephone. My
> total expense is about $160 which includes about $25 for 2nd day UPS
> from South Dakota to NY.
>
> .......It's going to be great to have an accurate cylinder head temp
> at last to look at while driving.
>
>

Huh! I guess the simple basic lack of understanding runs much deeper than
I possibly could have imagined. I wish you the luck that I didn't have:
The luck that the cylinder you place your monitor on is the one out of 4
that fails! For that much $$ you could have had a system that actually
works. Ah, well. I guess it's time to go back into hibernation.

--
-BaH
Dave Pearson
79 Bus w/ Subey 2.2
74 Bus Project

"Busahaulic" > wrote in message
...
>
> Huh! I guess the simple basic lack of understanding runs much deeper than
> I possibly could have imagined. I wish you the luck that I didn't have:
> The luck that the cylinder you place your monitor on is the one out of 4
> that fails! For that much $$ you could have had a system that actually
> works. Ah, well. I guess it's time to go back into hibernation.
>
>

........Sorry Dave, but my brain could never process four Westach CHT
readings while talking on the cellphone and eating a Big Mac and playing
with the adjustment on that dash mounted potentiometer and lastly trying not
to wander across the centerline into oncoming traffic..<g>...... My Berg
1679 has about 20K miles on it now and still has no changes in exhaust valve
length during adjustment/checking so I'm not too worried about whether 1, 2
& 4 are acting up for now. This Dakota Digital CHT gauge really does look
like a good upgrade over the VDO unit and I'll report back on how it's
working maybe next week after I get it installed this weekend.