temperature gauge

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William Trowbridge
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temperature gauge

#1 Post by William Trowbridge »

The needle on my 1964 SC coupe oil temperature gauge stays all the way to the right. Can someone tell me what is wrong and how I can get the gauge back in working order. Thanks, William

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Barry Brisco
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Re: temperature gauge

#2 Post by Barry Brisco »

William Trowbridge wrote:The needle on my 1964 SC coupe oil temperature gauge stays all the way to the right. Can someone tell me what is wrong and how I can get the gauge back in working order. Thanks, William
Hi William,

Everything I know about 356 electrical systems (which is not meant to imply I am an expert, I am NOT) I learned from Joe Leoni's books, see http://356electrics.com/books.htm. I think every 356 owner should own one.

If the circuit to the oil temp sending unit is open the gauge will read max (all the way to the right). Sounds like you have a poor connection or a broken wire between the gauge and the sender. Is this a new problem you are having with a gauge/sender combination that has worked correctly in the past?

Here is something Joe posted a few years ago:
Joe Leoni wrote:A couple quick tests.
Lif the green/black wire from the sender.
Igntion on, the gauge should go full scale.
Now ground the green/black wire, the gauge will register zero.

Lastly are you sure the green/black wire is connected to the temp sender?

The oil pressure is the green wire
.

And from another post he made last year:
There is the original and a modified sender/gauge.
To test the sender lift the grn/blk at the sender.
If original gauge, it will go full scale with the ignition on.
Now ground the grn/blk at the sender and the gauge will read zero.

The results are the opposite if your instrument has been modified.
Has it been to VDO?

Now to test the sender, wire off, ohmmeter to ground.
About 20 ohms at 20C for an original sender.
And easily over 200 ohms for the modified sender.

As always the grn/blk lands on the "G" for gauge.
Barry Brisco
1959 356A Coupe 105553, Ivory / Brown
2009 987 Cayman, Carrera White / Beige (daily driver)

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Herrick Griffin
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#3 Post by Herrick Griffin »

^ I take it the same posts would apply to someone with an temp gauge that is stuck all the way to the LEFT? That's the problem I've been having.
Herrick Griffin
1963 S Coupe

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Steve Domenicone
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#4 Post by Steve Domenicone »

If you want to rule out poor wiring and/or poor engine cooling or heating, you can take the gauge out and the temp sender and, with a 6V (or 12 if appropriate), some wiring and some hot water to dunk the sender in you can simulate the temp sender and gauge operation in a more controlled environment. Using the factory wiring diagram it was fairly easy to re-wire outside the car.

ENS Stephen Domenicone, USN

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Dave Wildrick
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#5 Post by Dave Wildrick »

Herrick Griffin wrote:^ I take it the same posts would apply to someone with an temp gauge that is stuck all the way to the LEFT? That's the problem I've been having.
It means your sensor is shorted to ground somehow.
Dave Wildrick
Houston, TX
#10230
64C coupe
65C coupe

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Dave Wildrick
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#6 Post by Dave Wildrick »

Steve Domenicone wrote:If you want to rule out poor wiring and/or poor engine cooling or heating, you can take the gauge out and the temp sender and, with a 6V (or 12 if appropriate), some wiring and some hot water to dunk the sender in you can simulate the temp sender and gauge operation in a more controlled environment. Using the factory wiring diagram it was fairly easy to re-wire outside the car.

ENS Stephen Domenicone, USN
According to Joe Leoni, at room temp. (74degrees F.), the sensor should read about 28 ohms when tested with a volt/ohm meter. (or 7 ohms at 20deg. C.)
Dave Wildrick
Houston, TX
#10230
64C coupe
65C coupe

Thomas Stukel
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Re: temperature gauge

#7 Post by Thomas Stukel »

Dave Wildrick's post says..."According to Joe Leoni, at room temp. (74 degrees F.), the sensor should read about 28...(or 7 ohms at 20 deg. Centigrade). This can't be correct; 74 degrees Fahrenheit is about equivalent to 20 degrees Centigrade. So, how could ohms be 28 at 74 Fahrenheit and then 7 ohms at 20 Centigrade (which is also 75 Fahrenheit). what am I missing?
Tom
'63 356B Coupe
'85 911 Coupe
Raleigh, NC

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Dave Wildrick
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Re: temperature gauge

#8 Post by Dave Wildrick »

Hi Thomas,
20 deg. C is 68 deg. F (not 74F or 75F); so the lower temperature generates less resistance; thus, 7 ohms instead of 28 ohms.

Here's my original correspondence with Joe Leoni in July of 2000:

[From: dwildric@mail.mdanderson.org <dwildric@mail.mdanderson.org>
To: 356talk@356registry.org <356talk@356registry.org>
Date: Sunday, July 09, 2000 12:44 PM
Subject: testing temp. sender


David wrote:

>Dear 356ers,
>My current temperature sender is probably shot. When the wire is connected
to
>the sender, the temp. gauge is pegged all the way to the left (full cold).
When
>I disconnect the wire, the gauge reads full hot--all the way to the right.
When
>I ground the sender wire, the gauge pegs all the way to the left.
>
>I have a second temp. sender, which has been in my toolbox for years, that
I
>would like to test. Is there a way to test it without installing it in the
car?
>I would prefer not to have to remove and install these things multiple
times
>because there is not much room to work in there and they are delicate (as
well
>as expensive). Thanks much!
>
>Dave Wildrick
>64 C coupe
>
>Hi David,
Your analysis is the process of checking the indicating instrument.
So the meter is okay.
Open sensor full scale, shorted sensor nada.
The sensor in the tool box, will read about 28 ohms at 74 F.
This is the temp in my garage this morning.
I think in our books we say 7 ohms at 20C.

However if you have had the Oil Temp conversion with the reverse
sensor all bets are off. Brad (NLA) is the expert in this area.

Sorry for responding so late, I have been in Durango.

Hope this helps.

Joe
356 Electrics
Downtown, Colorado]
Dave Wildrick
Houston, TX
#10230
64C coupe
65C coupe

Brad Ripley
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Re: temperature gauge

#9 Post by Brad Ripley »

A "late" sender will not work with your original gauge. There are no reproductions of the old sender. If you bought a new sender, you will have to have your gauge converted.

See http://www.stoddard.com/61610780501-nla.html

Ray Lolley
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Joined: Thu Jun 08, 2017 8:48 am

Re: temperature gauge

#10 Post by Ray Lolley »

Is this situation still the same?

is there any NOS anywhere?

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