Steve,
I assume the car was not running during these tests? When running the
system voltage should be around 14.5V if your alternator is good. Not
running, probably around 12.5. I know there is a "voltage regulator" on the
dash gauge circuit but the change in system voltage could be the culprit.
Aluminum is actually not that poor of a conductor so I doubt that it the
problem although dirt or corrosion on the thread surfaces might contribute
to a less than perfect ground connection. On the otherhand a poor ground
would result in a lower than actual temp reading so that doesn't make sense
anyway.
I'm not sure if Marks site is back on line but here is some temp sender data
that is either from Marks site or data I collected myself...
TEMP (F) OHMS TEMP (C) OHMS
212.0 19.6 100.0 19.6
201.2 36.0 94.0 36.0
197.6 36.9 92.0 36.9
194.0 38.2 90.0 38.2
190.4 39.5 88.0 39.5
186.8 41.1 86.0 41.1
183.2 42.9 84.0 42.9
179.6 44.6 82.0 44.6
176.0 46.4 80.0 46.4
167.5 49.7 75.3 49.7
155.7 56.7 68.7 56.7
147.9 63.0 64.4 63.0
139.5 74.0 59.7 74.0
135.0 79.8 57.2 79.8
121.1 84.6 49.5 84.6
75.7 207.0 24.3 207.0
You can see that higher ohms equals lower temps but higher voltage would be
like lower ohms to the gauge so the temps would read higher.
Frank
> -----Original Message-----
> From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net]On
> Behalf Of SJC Worldwide
> Sent: Thursday, April 26, 2001 12:50 AM
> To: Tiger Mailing List
> Subject: ??????
>
>
> Man, am I confused (even more than normal!). I took the temp sender out
> of the intake manifold, ran a ground wire to it, boiled a pan of water,
> ran back downstairs to the car and the garage with it, and measured the
> temp with my multimeter....about 190 degrees on that....the dash guage
> read 220 or so, about the same 30 degree srread I was getting yesterday
> when I measured the outside of the manifold with the multimeter. I
> figured I'd solved the mystery, that the guage reads about 30 degrees
> hotter than the water actually is. I ran upstairs again, boiled the
> water, ran downstairs again, seemed to get a little better ground on the
> sender, and now the mystery thickens....Multimeter reading in the pan of
> water.....about 200....Guage, barely over 200, pretty darn close. I
> tried this several times and now, when I made sure the sender was well
> grounded while taking the reading, dash guage readings and the
> multimeter were pretty close.
>
> My intake manifold is an LAT "Tiger" script lo rise, and I believe it's
> made of aluminum. Is this right? I don't think aluminum is a very good
> conductor for a ground, is it? I screwed the sender back into the
> manifold, but this time I've run a ground wire (I looped a wire around
> the very top of the sender threads so when I tightened it down the
> sender tightened onto the wire) to a good ground screw. It will be very
> interesting in the morning how the guage reacts with the sender now
> definitely grounded.
>
> Would a poor ground to the sender cause it to read higher than if it was
> grounded properly? I found tonight that with no ground at all the sender
> didn't cause the guage to move at all, and when I accidentally grounded
> the main wire to the sender (that goes to the guage), the needle pegged
> out all the way to the right, As soon as I was able to gound the sender
> body, the gueage reacted more normally. Hope this all makes sense.
>
> Anyway, after all this aggravation, I'm probably going to send the guage
> off the Mo-Ma anyway next week to have it properly checked and
> calibrated. Unless, that is, in some stop and go traffic tommorow the
> needle stays around 200-210 and doesn't creep up to 230-240.
>
> Steve Sage
> Spending way too much time late at night letting that @%%#^**^%%!!!!
> guage drive me nuts.
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