Temperature Gauge Sender Faulty?

[Mybikesacx500]

My temp gauge went from its normal 1/3rd position to near the top, then right past the top, then down to normal, then righ tup again, so I disconnected the wire from the sender, measured its resistance at 10 ohms, and ordered a OEM replacement from my local corner car spares shop.

Popped it in, all was well for 10 minutes of driving, then right up off the scale again.

Pulling the wire off the sender drops the gauge to zero.

So, 2 faulty senders, or a dodgy gauge?

Tried to find the sender resistance values, but my pdf manual just tells you how to check the gauge (earth it via a bulb, should move the needle up)

But no sender values, anyone know what the thing should read in a cold, hot engine?

I will double- check with another meter, but both senders read about 10ohm in a hot engine when I checked them with my iffy lives-in- the boot meter

cheers all

[steve2006]

Hi,

10 ohms sounds a little low at normal operating temperatures,you could always measure the output voltage when cold and monitor it as the engine reaches normal operating temperature to see if it alters correctly.

I have posted a link to typical expected measurements at various engine coolant temperatures but this is not model specific just a guide.

http://www.freeautomechanic.com/ect3.gif

You could try putting the sensor into some freshly boiled water then check the resistance as a comparison.

There could of cause be another reason for the high reading in that your engine is actually overheatin,g given the rising and falling of the gauge this could indicate an air lock in the cooling system giving flow problems

[Mybikesacx500]

Thanks for the quick reply, I to was initially concerned that the engine might actually be overheating, but with the new sender in this morning, with a stone cold engine, it gave me a right to the top needle deflection on the temp gauge, so either the new sender has gone faulty, or my gauge is bad.

The graph you linked to is, I think, for the ECT sensor, a 2-wire sender used by the engine management system as opposed to the humble little 1-wire sender for the temp gauge, which is my problem

10ohm does seem very low, but I need to check it with a better meter.

There is water present when I remove the sender, so not a lack of water, I think

Hi,

10 ohms sounds a little low at normal operating temperatures,you could always measure the output voltage when cold and monitor it as the engine reaches normal operating temperature to see if it alters correctly.

I have posted a link to typical expected measurements at various engine coolant temperatures but this is not model specific just a guide.

http://www.freeautom...ic.com/ect3.gif

You could try putting the sensor into some freshly boiled water then check the resistance as a comparison.

There could of cause be another reason for the high reading in that your engine is actually overheatin,g given the rising and falling of the gauge this could indicate an air lock in the cooling system giving flow problems

[SteveLS400]

I'm still having problems with my temp gauge.

After warming all 4 sender units in a pan the readings were all in the range 10 - 11ohms. My gauge works fine when shorted but nothing when connected. Its never overheated either before or since the trouble started. I have no idea why either of us have an issue.

[Mybikesacx500]

Thats good info, saves me repeating what you have done!

Sounds like it could be a gauge problem for both of us, mine goes full scale when connected, and yours doesn't move, interesting...

What we both need is more knowledge on how the gauge works

I will have a look round the American forum

I'm still having problems with my temp gauge.

After warming all 4 sender units in a pan the readings were all in the range 10 - 11ohms. My gauge works fine when shorted but nothing when connected. Its never overheated either before or since the trouble started. I have no idea why either of us have an issue.

[ROYT]

Thats good info, saves me repeating what you have done!

Sounds like it could be a gauge problem for both of us, mine goes full scale when connected, and yours doesn't move, interesting...

What we both need is more knowledge on how the gauge works

I will have a look round the American forum

I'm still having problems with my temp gauge.

After warming all 4 sender units in a pan the readings were all in the range 10 - 11ohms. My gauge works fine when shorted but nothing when connected. Its never overheated either before or since the trouble started. I have no idea why either of us have an issue.

Gauge sender info from w/shop manual:

Water temp. 50 deg.c [122f] resistance approx 249 ohms

" " 115deg c [239f] " " 28 ohms

[Mybikesacx500]

More great info, I will get some readings from the original sender

Gauge sender info from w/shop manual:

Water temp. 50 deg.c [122f] resistance approx 249 ohms

" " 115deg c [239f] " " 28 ohms

[Mybikesacx500]

Just measured my replacement sender in the car, 5 mins after a long run, used my old Fluke as opposed to the car- boot meter I kept in the car,

103ohms, so that seems about right, re-connected the wire, and the gauge shot through the roof- faulty gauge, then.

Anyone seen a cct. diagram that gives any details on the gauge?

The old meter happily says the resistance is 10 ohm- wrong, that's what LED me to get a replacement sender, oh, well....

[SteveLS400]

Just measured my replacement sender in the car, 5 mins after a long run, used my old Fluke as opposed to the car- boot meter I kept in the car,

103ohms, so that seems about right, re-connected the wire, and the gauge shot through the roof- faulty gauge, then.

Anyone seen a cct. diagram that gives any details on the gauge?

The old meter happily says the resistance is 10 ohm- wrong, that's what led me to get a replacement sender, oh, well....

And its over a year since my pan boiling so 10/100 is easily lost in the mists of time.

Now, have you shorted the sender? Soon as I do mine to the Battery,the gauge goes straight up to the "roof" as you put it. Maybe your wiring from the sender to the gauge is chaffed/shorting. If it makes you feel better I bought 2 brand new senders and Benfur supplied the other. The result remains with the gauge anchored to the "floor."

[steve2006]

Just measured my replacement sender in the car, 5 mins after a long run, used my old Fluke as opposed to the car- boot meter I kept in the car,

103ohms, so that seems about right, re-connected the wire, and the gauge shot through the roof- faulty gauge, then.

Anyone seen a cct. diagram that gives any details on the gauge?

The old meter happily says the resistance is 10 ohm- wrong, that's what led me to get a replacement sender, oh, well....

You can't beat a Fluke DVM

I have a working 90-92 complete dash if you want to borrow it for testing purposes.

[Mybikesacx500]

Yep, it's an ex-forces from eBay ancient thing, but its a Fluke

That's a generous offer, I think I will have a look at mine first, see if anything obvious has gone- hoping for a burnt out resistor, or dry joint.

My gauge sits at the bottom, until I conect to the sender, which has a resonably correct resistance, and then the needle flicks right up

You can't beat a Fluke DVM

I have a working 90-92 complete dash if you want to borrow it for testing purposes.

[SteveLS400]

Yep, it's an ex-forces from Ebay ancient thing, but its a Fluke

That's a generous offer, I think I will have a look at mine first, see if anything obvious has gone- hoping for a burnt out resistor, or dry joint.

My gauge sits at the bottom, until I conect to the sender, which has a resonably correct resistance, and then the needle flicks right up

You can't beat a Fluke DVM

I have a working 90-92 complete dash if you want to borrow it for testing purposes.

please keep us posted

[Mybikesacx500]

I had the dash out yesterday and back in today, managed to break all 3 of the clips along the bottom of the dash surround ( tip to anyone doing this for the first time, take out the top 3 screws, then pull out straight, dont pull the top edge out to far before levering the bottom edge straight out) the clips were very tight.

I was all ready to do the capacitor change thing, but it seems I have a different (earlier?) unit.

I removed and cleaned the inside of the dark plastic cover, it was very dirty on the inside, removed and cleaned the cover of the mechanical odometer. I checked all the bulbs, and looked very closely for any damaged components around the temp gauge connector. I also re-soldered everything in that general area.

Put it back in, everything worked, and was very clean and sparkly. The temp gauge also seemed to be working, didn't imediately shoot up. Went for a run, after 15 minutes, sure enough, the temp needle went from its usual 1/3rd and wavered up and down,then went fully up. Unpluged the sender cable and the needle droped down to the stop.

Very frustrating, I can just picture some 20p component warming up a bit and failing,and it would be easy enough to change as it's a standard old style cct board with components soldered into holes, but without a cct. diagram for a Denso 457952-0495 board, I don't know what to look for.

I also have a main beam indicator lamp that went very dim and then didn't come on at all, doesn't seem to be the bulb

So whould anyone have a diagram, or a cct board to sell. or a complete dash?

[SteveLS400]

PM Benfur