Lotus Elan

Where in the UK to get a temp gauge repaired?

PostPost by: john.p.clegg » Tue May 27, 2014 7:02 pm

"with a little luck a resistor in-line between the two will do the job,an infra-red temp sensor and a rheostat box would sort you out........"It's not as simple as that...you need an infra red sensor to check the actual temperature at the sender and a rheostat box in-line to adjust the reading,only then can you get down to Maplin etc and solder a resistor in line (mine's at the sender end )..

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PostPost by: Johnfm » Tue May 27, 2014 7:58 pm

I have an infrared temp gauge thing.

No rheostat - thought I I suppose I could get a cheap variable resistor from ebay or similar, wire it in and then adjust until gauge reads correctly.

Any estimate as to what range the resistance might be in?
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PostPost by: john.p.clegg » Tue May 27, 2014 8:24 pm

You're looking in the range 300 down to 20 Ohms,you could multi-meter the sender at operating temperature and then use a small potentiometer to get you a figure...

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PostPost by: Quart Meg Miles » Tue May 27, 2014 9:42 pm

Johnfm, sorry I highjacked your thread. :oops:

Do we assume that your 10V regulator is working correctly?
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PostPost by: rgh0 » Wed May 28, 2014 1:19 am

Check the voltage regulaltor is giving you 10 V first.

As an alternative to buying a variable resistor and adjusting the setting to determine what fixed resistance to add you can try the following

Measure the resistance of the sender when the guage reads around 80 to 90 degrees ( but the engine coolant is actually cooler. That is the resistance you will need when the engine is at its normal 80 to 90 degrees operating tempreature actually to bring the guage back to an accurate reading. Now heat the engine to its normal operating temperature at which the guage reads the higher approx 120 C number and measure the sender resistance. The difference between the two resistance readings is what you have to add to bring the guage back down to the accurate reading.

cheers
Rohan

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PostPost by: stugilmour » Wed May 28, 2014 5:18 am

Agree check the voltage stabilizer first. It is a small metal box usually attached to one of the tach mounting thumb screws. If you can't get a good 10v reading, it may be pouched, or one of the original bi-metallic type that can't be accurately measured with a digital voltmeter. For under $20 replacement rules out an issue. I got a replacement from Moss Motors, and found their write-up helpful. The stabilizer supplies the temperature and fuel gauges in the Plus 2.

http://www.mossmotors.com/graphics/prod ... 31-555.pdf

I followed advice here and did the same as John by adding resistance at the sender. Just bought a blister pack of about 100 resisters from Radio Shack for about $10. Trial & error of a few values brought the gauge in range pretty quickly. Recall that putting resistors in parallel with one another alters the total resistance, so you can dial in the value pretty accurately.

http://www.sengpielaudio.com/calculator-paralresist.htm

http://www.digikey.ca/ca/en/mkt/calcula ... stors.html

The small resistors I used needed a couple in parallel to keep from overheating. Covered the soldered resistors with heat shrink. Only going from memory, but I think the total required resistance value was about 20 to 40 ohms. Figure the added resistance just makes up for a bit of spring loss in the gauge movement.

As I have a Clivey Boy thermostat housing with a blanking cap, I was able to get an accurate coolant temperature using a glass candy thermometer (from the grocery baking section) immersed right next to the sender.

HTH

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PostPost by: Johnfm » Fri Jun 06, 2014 7:01 am

Stabiliser seems not to be putting out 10v - was more like 12v and a bit.

I will try replacing that first.
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PostPost by: billwill » Fri Jun 06, 2014 10:33 am

Johnfm wrote:Stabiliser seems not to be putting out 10v - was more like 12v and a bit.

I will try replacing that first.



If you have an original vibrating stabalizer you need a very sluggish meter to measure its output, because it consists of Battery-Voltage pulses which AVERAGE 10 volts.
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PostPost by: Johnfm » Fri Jun 06, 2014 10:58 am

It looks a bit newer than circa 1967.

Given my enigne isn't overheating, yet temp gauge shows 120+ degrees, I suspect the stabilser is toast.
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