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 Posted: 10-22-2006 01:30 pm
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John Kimbrough
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For several months now, my temperature guage has been reading very low (it seems) and now it is not reading at all.  My gas guage seems to be working fine, so I don't believe it is the regulator.  Suspect is the temperature transmitter.  Since there is but a single connection on the transmitter, I assume it must be grounded through the engine.  If so, if the connection between the transmitter body and engine is not good (like the thread sealant is insulating it) then the guage would not work. 

Has anyone measured the resistance across the transmitter to see how it changes during engine heat-up?  Mark, I seem to remember you doing this in another life.  I would be interested in checking out the whole circuit using a variable resistor in place of the transmitter if I knew the range of the transmitter resistance.  That way I could isolate the problem. 

Also, does anyone know of a transmitter that has both a guage and a ground connection so I can take an iffy ground out of the mix? 

Any thoughts???  John.

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 Posted: 10-23-2006 04:10 am
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Mark Rosenbaum
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Dealing with a cold today so pardon me if I'm brief.  Disconnected, the temp gauge should read about 60 ohms across its terminals.  Sender behavior is nominally as follows:

Temp Temp Sender
°C.....°F.......Ohms
 25......77.....820
 50....
 122....306
 70.... 158....170
 80.....176....142
 90.....194....106
100....212......
79

There may be further useful info in the very early posts in this section.

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 Posted: 10-23-2006 08:06 pm
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John Kimbrough
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Thanks, Mark, this is just what I needed.  I have also read all the other posts in Cooling and Instrumentation on this subject.  Just couldn't find the resistance table.  John.

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 Posted: 10-24-2006 01:33 am
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Ron Earp
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If you want a new gauge you can get a mechanical gauge that will fit in the hole perfectly, or electrical, your choice. I used a lot of Autometer gauges, 2 1/16 size, fit perfectly. On the electrical gauges most do ground through the body, but a lot of the sensors also have a tab you can put a push fit female terminal onto to ground via a wire if you like.

Ron

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 Posted: 10-28-2006 10:06 pm
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John Kimbrough
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Well, to wrap things up, I removed the water temperature sending unit wire and when I grounded it, the water gauge needle moved over to the hot side indicating that the gauge was working.  Then I checked the resistance from the tab on the sending unit to the manifold and it was essentially an open circuit.  I thought it might be the ground between the sending unit and the manifold so I removed the sending unit, checked the resistance and it was essentially an open circuit.  Even when I immersed the sending unit in boiling water the sending unit remained an open circuit. 

Ordered a new sending unit today.  Thanks Mark and Ron for the help and advice.  John.

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 Posted: 10-30-2006 05:47 pm
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Joel
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While you have it out - toss it in the can and buy a mechanical unit that gives you a real temp reading instead of 'it's approximately 1 needle width north of center'.  I really like being able to read the actual temp. 

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 Posted: 10-31-2006 01:26 pm
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Ron Earp
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I'm a big fan of mechnical units and bought a full set of SW mechanical gauges to fit in the Lola. I like the simplicity of them and the fact there is no wiring to worry about besides the lighting. But it is a common misconception that analog electrical gauges don't read accurately or consistently.

There are some articles on comparisons in some of the race magazines between the two types, but electrical gauges more than hold their own against mechanical gauges. We've done comparisons ourselves with Autometer electrical gauges vs. SW mechnical gauges and found the Autometer gauges were a bit more accurate in absolute value and showed a faster response time when going from temperature differentials.

However, the mechanical gauges are simple, typically robust, and still are most common in harsh use. I know I like them for ease of use, but the electrical gauge (a good one) gets an undeserved bum rap.

Now, I don't know if the electrical gauges in the JH are worth a damn or not, so don't let this influence your choice there. Does it even have a temperature scale on the face?

Last edited on 10-31-2006 01:27 pm by Ron Earp

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