Temperaure Gauge woes!

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gone_left
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Temperaure Gauge woes!

Post by gone_left »

I've only owned my T25 for a short while and when I bought it the temp gauge did not work, so I replaced the sender on the thermostat housing. Now after starting the needle climbs quickly (within a couple of minutes of having the engine on, even if just idling) to sit a couple of degrees away from the high end of the scale and the red light of doom starts to flash.

I have checked the resistance across the pins of the sender is over 100ohms which should mean the needle sits much lower and the light shouldn't be flashing.

I also checked the voltage across the sender (which I think should be 10vs?) and I get 9.99 on my multimeter, but the voltage drops for a second or two every 20 seconds or so. Usually it drops to around 3v but can vary and then it will sit at 9.9 again only to drop again. This is only happens when the engine is running not if it just on the ignition.

I have replaced the voltage regulartor in that back of the dash but it has made no difference.

Is it time for me to get a new set of clocks or is there anything else I can try?

Thanks in advance
1986 1.9 DG Holdsworth Villa Mk3 Pop-Top

boatbuilder
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Re: Temperaure Gauge woes!

Post by boatbuilder »

Have you checked the sender on the top of the coolant header tank?
It can cause the red light to flash and the needle to go to max...
1984 1.9D (AEF Code) T25 tintop

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marlinowner
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Re: Temperaure Gauge woes!

Post by marlinowner »

Sounds like it could be the coolant level warning, assuming the expansion tank is full (the one in the engine compartment not the one behind the number plate flap), then pull out the "relay" marked 43 or 42 and see if that stops the flashing.. If not then could be an earth problem, the earth connection to the warning light circuit is the middle of the three on the back of the gauge and can cause this.
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gone_left
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Re: Temperaure Gauge woes!

Post by gone_left »

Sorry boatbuilder I should have mentioned in my original post that this all occurs with relay 43 disconnected so the low level sensor can be ruled out.

Thanks for the earth suggestion marlin. I have been doing a bit of reading since my original post and was thinking the nuts on the back of the gauge should possibly be my next port of call so I'll give it a try?

Thanks
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AngeloEvs
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Re: Temperaure Gauge woes!

Post by AngeloEvs »

I covered a lot of temp gauge issues and how the system functions in a thread " Overheating Query" which you can find by scrolling down in the mechanical section.

Which thermostat housing do you have - plastic or aluminium?

If the temperature gauge was not functioning before you replaced the sender and, having replaced it, it now swings hard right then something is amiss with the sender or the connections to it given that the engine is only being run for a couple of minutes.

Does the gauge swing hard right with just the ignition on and module 42/43 removed. If it does then you have a wiring short to earth as the most likely cause.

Did you measure the senders resistance with engine cold or when the gauge was fully deflected and the led flashing?
1987 DG Karisma LPG with remodelled interior

gone_left
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Re: Temperaure Gauge woes!

Post by gone_left »

Thanks Angelo, I read through the "Overheating Query" thread and it's been a massive help in getting me to where I am so far but I don't know where to go next.

The needle swings hard right even with module 43 removed and the light will still flash. I had a mess around with the dash in my lunch break today and checked the earth/connections on the blue ribbon with a multi meter and it was as I'd expect. I have realised though that with module 43 removed the light only normally starts to flash when the needle gets 3/4 of the way across the gauge, but if I turn my lights on the LED will start to flash immediately, which does make it sound like a short somewhere.

I have the plastic thermostat housing - does it make any difference?

The 100hm measurement across the resistor was taken when the red light was flashing and the needle was hard right.

Thanks for the help.
1986 1.9 DG Holdsworth Villa Mk3 Pop-Top

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marlinowner
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Re: Temperaure Gauge woes!

Post by marlinowner »

To me things going wrong when lights are switched on points to an earth problem, when the lights are off there is a route to ground through the bulbs which is lost when they are switched on. Try running a wire directly from the middle terminal of the gauge to ground. The gauge going full over sounds like a separate fault, what happens when the temp sender is disconnected?
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1981/1968 Marlin Kitcar TR6 Engine

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AngeloEvs
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Re: Temperaure Gauge woes!

Post by AngeloEvs »

Test wether the lights affect the temp LED and wether the guage goes full scale with-

1. just ignition on

2. the sender disconnected

I would measure the resistance across the gauge to earth at the gauge itself by removing the cover and accessing the three nuts, the middle one is earth. I would take readings first with ignition off, then with ignition on, then with engine running after a few minutes.
It seems as if your gauge is connected to something other than the sender but this has only started since you replaced the sender. There are two similar devices in the plastc housing, one is the sender the other is a thermal switch. Are these in their correct locations with the correct wiring to them?

I am in the Leicester area most weekends, sometimes close to Loughborough PM me your number.
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ronsrecord
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Re: Temperaure Gauge woes!

Post by ronsrecord »

Angelo - all the recent advice is so valuable! would be great if it could be put together for the wiki
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Re: Temperaure Gauge woes!

Post by chewbacca »

Are you sure it's the correct sensor you have in there?
I had the exact same problem. Purchased a new sensor to try from my local auto-factors because I was having problems.
Once I'd fixed the real issue, it appeared to be overheated very quickly according to the temp gauge, which it clearly wasn't. I put the original sender back in and everything was gravy.
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gone_left
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Re: Temperaure Gauge woes!

Post by gone_left »

ronsrecord wrote:Angelo - all the recent advice is so valuable! would be great if it could be put together for the wiki

I second that; Angelos advice in this and other threads is what got me this far.

I've had a bit of a mess around this weekend and added an extra connection from the middle nut on the back of the gauge to an known good earth point beneath the dash. I've also cleaned up the earths in the engine bay but neither seems to have had an effect. This is where my gauge sits.
Image

If I turn my lights on with the gauge this height the LED will immediately start flashing.

With just the ignition on the gauge goes nowhere same with the gauge disconnected. If I drive around with my lights off the gauge takes a longer to get this high but will eventually get there and the LED start to flash.

All this is with module 43 disconnected.

I have thought that perphaps I have caused the problem with by connecting the sensor incorrectly so I will have a look and see if I can swap the connectors for the 2 sensors on the thermostat housing but I have a feeling the plugs are different shapes. I will also try and get a multimeter onto the sensor to see what the resistance is when cold.

I got the sensor from justkampers but I will try and find the receipt and just make sure it is the correct one.

Thanks again for all the help everyone.
1986 1.9 DG Holdsworth Villa Mk3 Pop-Top

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Re: Temperaure Gauge woes!

Post by Ads1987 »

Hi,

Did you manage to fix this issue, I'm suffering with the same fault!

Thank you,

Adam.
1982 T25 1.9 DG model with 4 speed box

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