Temperature gauge now reads low

[olr159w]

Those of you following my maze of different threads will be aware that I’m trying to get my Sprint back on the road. It’s progressing OK with the brakes repaired and the engine/gearbox mounts replaced. Remaining work relates to one front shock and the fuel line clips really and parts are in the post for that.

I started the engine again the other day having re-torqued the head and done a few other bits and pieces. That was all good except that the temperature gauge took a long time to register anything. I live in a hot environment so the normal situation is that the engine warms up fairly quickly and then the gauge sits a little over halfway unless it’s stuck in traffic when it could potentially get up to 3/4.

Nothing else has been changed or touched electrically other than fitting a new flasher unit. The cooling system is topped up and as far as I know both the thermostat and oil cooler are working as before.

The issue is that the temp gauge took a while to move and when it finally did its operating position didn’t reflect much movement – something like 1/4 or thereabouts. The car was still on stands so this was a static exercise.

There’s nothing I know of that could make the car perpetually run cooler – in normal operation the thermostats would open and utilise the radiator and oil cooler but this is to stop the engine getting too hot rather than magically actually keeping it cooler. I suspect either the gauge, sender or voltage stabiliser. Since the gauge did move I am less inclined to think it’s that which leaves us with the sender or voltage stabiliser. The other gauges were OK I think – I didn’t really check but I don’t remember anything out of the ordinary. Which maybe just leaves us with the sender unit.

Any thoughts on that logic or other advice? Any tests I can do to determine the cause. Being a Sprint, of all the gauges you’d want to have working correctly it’s the temp gauge that heads the list of course

Thanks

[GTS290N]

The voltage stabiliser provides 10V to the fuel gauge and the temperature gauge, and that's all. You can try to measure the output of the regulator but as it's a mechanical device sometimes this isn't possible. Use a 7810 voltage regulator in a TO-220 package, costs pennies and gives an accurate 10 volts out. If you need a new temperature sender get it from Robsport, they were using a type more akin to the original, Rimmers were using a land rover replacement.
http://www.ebay.com/itm/10pcs-New-L7810 ... 1045058247

[Toledo Man]

An easy way to test the temp gauge is to remove the connector from the sender and connect it to an earth. It the gauge goes all the way into the red it is working. I second the Robsport recommendation for the sender.

[SprintMWU773V]

I would imagine 99% of issues like this are down to the voltage stabiliser. If you read less than 10.2v then you'll under read, more than and you'll over read. The original design is quite antiquated whereas a modern 'solid state' type one will give more accurate readings, albeit when they go wrong they just don't work at all.

[Carledo]

This may be as simple as a dirty connection between the wire and the sender increasing resistance and giving a false reading, my Vauxhalls are b****rs for this!

Steve

[olr159w]

Thanks all.

I just did some checks. The current stabiliser is the same product shown on the Rimmers page. I don't know if that means its solid state or something else. Not too sure how a voltage stabiliser could be mechanical though?

When I put the voltmeter on the stabiliser output it seems to vary constantly between about 2V and around 8V. Hard to tell with a voltmeter but it seems to be oscillating up and down within that range so assume its stuffed.

Where is the best place to get a solid state version?

I also earthed the sender cable to check the gauge. It did move straightaway although it never reached more than 7/8 of the way up. The battery may be a little under charged by now and perhaps at 11.5V or so.

I'm assuming the gauge might have been expected to reach the top marking and keep going until it hit its physical limit? Are the gauges adjustable for end stop?

thanks

[dursley92]

Might be worth getting one of those IR Thermometers to check the actual temperature of the engine/thermostat cover to put your mind at rest, they are quite cheap these days, £10-15.

[markas]

The other gauges were OK I think – I didn’t really check but I don’t remember anything out of the ordinary.

Fuel gauge readings are also affected by the voltage regulator - might be worth checking out although if the car's still laid up it could be difficult.

[GTS290N]

.....

Where is the best place to get a solid state version?.....

The club used to do plug and play versions, maybe they still do?
I had a look at electronics stores in Perth and they all do 5v, 6v, 8v, 12v, 15v, 24v but no 10v - what have you guys got against the number 10?
Try these people:
http://au.rs-online.com/web/c/semicondu ... hTerm=7810

[MIG Wielder]

Thanks all.
I just did some checks. The current stabiliser is the same product shown on the Rimmers page. I don't know if that means its solid state or something else. Not too sure how a voltage stabiliser could be mechanical though?
When I put the voltmeter on the stabiliser output it seems to vary constantly between about 2V and around 8V. Hard to tell with a voltmeter but it seems to be oscillating up and down within that range so assume its stuffed.

thanks

It may sound strange but my guess is that your voltage stabiliser is working. Bear with me for an explanation.
The Dolomite water temp; gauge ( and the fuel gauge) are both thermo; reading instruments which means the gauge reading is proportional to the RMS ( Root mean square or heating value) of the stabilised output voltage.
The way this mechanical stabiliser works is to mark-space on and off the 13.5 V input voltage to produce a 10V +/- 0.5V RMS output voltage. So it does this by switching the output voltage from 0V to +13.5 V input voltage at a fast rate. If you measure the output with a True RMS voltmeter you will get 10V. If you measure with an average reading voltmeter you will get a reading depending on how the voltmeter responds to pulsed d.c. voltage. So when you see the voltage pulsing between 2V and 8V all it means is that your particular meter is a fast reading averaging meter calibrated to read D.C. An oscilloscope will tell you the true picture. If there is any interest I'll see if I can get a trace.
HTH,
Tony.

[olr159w]

Thanks.

A few things:
a) fuel gauge appears to work correctly ie it works and registers low which is consistent with known fuel level in the tank
b) looking on ebay there are people who provide stabilisers that are solid state within traditional housing. That's what I'd be looking for
c) IR gun might be a good idea - where can you get one for 15 quid though?
d) Might the gauge be dodgy if it only travels to 7/8 anyway
e) MIGW - take your point about switching nature of stabiliser. It would appear that's what its doing. However it never read 10V and was generally moving between 2 to 3V and around 8V. So that might be an issue?
f) did all these tests with engine not running

Any further comments welcome !

[Carledo]

Since your fuel guage appears normal, I doubt the voltage stabiliser is duff!

Whenever i've earthed a temp sender lead, the guage has gone quickly as far as it can to the right, this means WAY past "hot"

So I would suspect either the guage is lazy (or duff) or there is some fault in the wiring between the guage and sender.

As a final check before trying a different guage, access the back of the guage, remove the lead to the sender (green/blue trace IIRC) and use a jumper lead to earth the guage directly. This will eliminate everything downstream of the guage and you can proceed accordingly.

If the guage STILL only goes to 7/8 under these test conditions, unlikely as the scenario is, I reckon the guage will be at fault. I have several known good guages here and would be pleased to send you one for the cost of postage if you can't find one there.

One last and not very likely possibility, check and clean all the green wire connections at the fusebox, this is where the stabiliser draws its power and a high resistance here could affect things. But since the fuel guage is OK I doubt this too.

Steve

[olr159w]

Useful thoughts thanks. I'll try that direct earthing of the gauge at the weekend and respond with the results. I may do likewise for the fuel gauge just to see how that's faring as well.

[Carledo]

I may do likewise for the fuel gauge just to see how that's faring as well.

Good idea, it will give you a comparison! Remove the green/black trace wire from fuel guage to test that one.

Steve

[olr159w]

OK I carried out the test on both gauges.

They both went up to 3/4+ to 7/8 of their scale. This was the same extent seen via the loom wiring for the temp gauge and since both gauges seem to have approx. the same limit I still think it's worth replacing the voltage stabiliser

What do people think of this :

http://www.ebay.com.au/itm/New-Digital- ... SwZQRYYcam