Temperature Gauge changing based on Electrical Usage

Conda

Conda

Daily Driver
Hey guys,

I've been noticing over time that my head temp gauge on my 87 X1/9 seems to vary based on the other systems that are being used on the car. For example, headlights on makes about a 10 degree (Fahrenheit) increase in temp, turn signal will make the temp gauge shake with the signal timing, and turning the radiator fan on will also increase the reading on the gauge.

The end result is that sometimes my gauge starts worrying me until I shut everything off and it drops back down to ~195 or so, but I still feel like my actual temp may be inflated by constant electrical usage.

Does anyone know if there is a ground that needs to be added or some sort of change that can be made to stabilize gauge cluster readings more? I will pull the cluster later and post pictures and look for potentially loose connections.

Thanks all.
 
The gauge is powered by your +12V and ground wires, and the sense line is from the mounted sensor.
If your 12v source varies, you will get the effects you describe.
Fortify your voltage source by changing the battery ground wire to a new 4Ga Ground terminal and attach it using a SS star washer to ground at the chassis point.
Insure that the ground wire from the back of your transmission (to chassis in the engine compartment) is of good integrity. Replace it if not.
Also, double-up on the 8Ga brown wire that runs from the battery to the distribution point of your electrical system. The entire electrical system will benefit from this.
Lastly, be sure your Temp Sensor has clean threads when screwed into it's mount. You don't want corrosion around the threads.
Hope this helps!
 
I was thinking about this just the other day, whilst making my new cluster - most manufacturers added voltage stabilizers to the clusters going back to the 80's - - just a transistor (correct me if I'm using the wrong terminology, Bob) that provides a stable output voltage to the gauges regardless of system fluctuations caused by load changes. One could be added to the cluster, however it wouldn't really negate the other work Bob mentioned that is needed to make the system as sound as it can be otherwise.
 
You can also use a voltage regulator IC. Just make sure you select one with sufficient current, voltage, and power capability and make sure it is appropriately heat sinked. The app notes should have the info you need to hook it up. This should make the readings more repeatable but accuracy is a different matter.
 
I have used a capacitor to do this. especially in the 80's when we have "thumping" systems that the bass would pull more voltage during the thump. (also used in a cross over to smooth out the high frquencies)

odie
 
lookforjoe said:
was thinking under 2buck regulator IC, not a $30 item
Click to expand...
Ya, my reference was only to illustrate the component - not the price or supplier. As noted those are a common inexpensive item, but I thought having the description to go with it might help. I suppose the real benefit here would be if someone could detail how to install one into the X's cluster.
 
Dr.Jeff said:
Ya, my reference was only to illustrate the component - not the price or supplier. As noted those are a common inexpensive item, but I thought having the description to go with it might help. I suppose the real benefit here would be if someone could detail how to install one into the X's cluster.
Click to expand...

The problem is just that since the VR has to be attached before the gauges, it would need to be between the power supply and the cluster connector. That would be the tricky bit here.
 
Perhaps there is a convenient spot somewhere to break the power feed line to the cluster and stick a regulator in. However, if the voltage throughout the car is varying enough to cause problems, a better use of time might be to find the root cause. Personally, I'm not sure all the factory gauges are accurate at any one supply voltage. If you wanted to get fancy, you could put a regulator on each one and calibrate them individually.
 
Conda said:
Hey guys,

I've been noticing over time that my head temp gauge on my 87 X1/9 seems to vary based on the other systems that are being used on the car. For example, headlights on makes about a 10 degree (Fahrenheit) increase in temp, turn signal will make the temp gauge shake with the signal timing, and turning the radiator fan on will also increase the reading on the gauge.

The end result is that sometimes my gauge starts worrying me until I shut everything off and it drops back down to ~195 or so, but I still feel like my actual temp may be inflated by constant electrical usage.

Does anyone know if there is a ground that needs to be added or some sort of change that can be made to stabilize gauge cluster readings more? I will pull the cluster later and post pictures and look for potentially loose connections.

Thanks all.
Click to expand...
The cluster in the X1/9 uses dual coil gauges, and these are quite insensitive to supply voltage variations. If the ground connection for the gauge or the sender (or both) is questionable it will affect the accuracy of the gauge. I would first check the ground for the cluster (ground bloom under the dash, left of the steering column). Check that the connector makes a good connection to the ground bloom, and that the ground bloom makes good contact with the body. Engine to body grounds are important too, but you'd probably notice starting problems if there was a problem here.
 
Dr.Jeff said:
Ya, my reference was only to illustrate the component - not the price or supplier. As noted those are a common inexpensive item, but I thought having the description to go with it might help. I suppose the real benefit here would be if someone could detail how to install one into the X's cluster.
Click to expand...

Apparently this part (for VAG applications) is a TCA700Y which is not so common (hence the prices). Apparently you can use a L7810CV as a replacement (only about $1) but the pins are reversed.

In any case, I'm with Bjorn on this: it certainly sounds like a bad ground.
 
Step 1 with ANY DC electrical issue. Check for Good grounds! I have seen this many times on many automotive forums. and 90% of the time they are right.

Odie
 
dcioccarelli said:
Apparently this part (for VAG applications) is a TCA700Y which is not so common (hence the prices). Apparently you can use a L7810CV as a replacement (only about $1) but the pins are reversed.
Click to expand...
Thanks for that info Dom. I'll have to look closer - several years ago I bought a spare to have on hand for my VW projects and it was very cheap. So it may be the "reversed" layout version. ;)
 
Guys, those TO-220 devices don't buck/boost voltage without additional circuitry.
Even the best "voltage regulator ICs" needs 0.5v more voltage than they can regulate.
If you have less than a 12V supply in this case, you will need DC to DC conversion. The one I chose
would also supply the current needed for the entire cluster. You will need more than 2 amps ...
especially if you are using incandescent lamps.

Or, you can save all this hassle by making sure the supply voltage from the battery is adequate
(good wire) and that the grounds are proper. (good grounds). :-D
 
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So looking at the car yesterday, I have previously cleaned up the ground bloom under the drivers side dash. I will increase the size of the ground wire from the battery to the frame. I have previously had trouble starting due to a ground issue between the engine block and the frame, so maybe I should replace that strap instead of just cleaning it up.
 
When you upgrade the negative battery cable up front, you can use the old one cable to piggyback on the strap connection at the rear frame.
 
You can get
Conda said:
So looking at the car yesterday, I have previously cleaned up the ground bloom under the drivers side dash. I will increase the size of the ground wire from the battery to the frame. I have previously had trouble starting due to a ground issue between the engine block and the frame, so maybe I should replace that strap instead of just cleaning it up.
Click to expand...
decent ground straps off Amazon -

I bought this one - there are shorter lengths of the same product. This is a good quality version

https://www.amazon.com/gp/product/B0016HUSVC/
 
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