Dodgy temp gauge

[Terapixels]

My temp gauge keeps flickering. Having lost my green one to coolant loss I am very nervous now. Video enclosed. What do people think?

[Simon Jones]

It seems to move with engine speed which would indicate a problem with the voltage regulator. I can't recall exactly where about it's fitted, but will probably be somewhere on the back of the instrument panel. I may have one in the shed so can pop out to have a quick look.

[Simon Jones]

Here's one I made earlier...

I think it's the 3 legged device which you can see towards the middle bottom:


Here it is from the front:


This instrument panel was from a Mazda 626 and there are a few differences so I don't think it could be used 'as is', but if you're handy with a screwdriver and a soldering iron then you could transfer the part over. You can have the remains of this for a few beer tokens plus postage if that's any use. Alternatively, I can desolder the component and stick it in the post for free

If anyone could confirm for definate whether this is the voltage regulator or not. It does seem to have one leg connected to a bulb so it could perhaps be something like a low petrol indicator? No point in wasting your time if this is not the right thing.

[jaylee]

What is the alternator pushing out...?

[tallbongo]

Looks like a TO92 package, which lots of devices come in. Can you read any of the lettering on it?

Mosfets are a device commonly in this package and more consistent with having one leg hooked up to a bulb. If it was a voltage regulator the legs would be 12Vin, V out and gnd.

[teenmal]

Hi,
It looks like a bad sender or connection on the sender,try cleaning the connections first.

Cheers.

PS do you have a Mason alarm fitted?

[maxheadroom]

when mine did a similar thing to this it was the water pump. I was on the M4 at the time and the needle would travel to over half way and then back down to zero at around the same speed as your needle.

[Northern Bongolow]

the gauge itself works by measureing the difference between 2 coils within the gauge itself, these coils terminate at the posts that support the gauge in the cluster, these posts are what the mounting screws screw into, if these screws are tightend/loosened the post can twist and snap the very thin wires to the coils. it maybe that someone has broken a wire inside the gauge or it has a bad connection inside.

the fact that it seems to be rev related may point to the voltage out of the alternator, stick a meter on it and measure the volts and the amps out when reving and resting.

or the harness that carries the live to the top of the sender is at fault. this harness comes over the top front of the rocker cover and is very short in length and can cause a bad connection to the top of the sender. the sender is under the drivers seat at the front of the head,it has a single wire running to it, remove and clean sometimes works.
with the engine running/warmed up put a meter to measure the voltage at the sender top terminal, if i remember correct it should be about 6 volts, check the voltage is consistant, if it is see below.
could be the earth strap to the engine, as the engine revs it tips slightly so it could be the strap thats got a bad connection to the body (bad earth).

maybe an idea to put a GA5R speedo head in out of a mazda 626, so the speedo reads in miles on the main outer and kph on the inner.

(hows that double din doing mate)

[Simon Jones]

You raise a good point Ady: that speedo still shows KMH at the bottom which by rights should be an MOT failure, even if a chip has been fitted to reduce the reading to show MPH.

[Terapixels]

Steady on Prof Ady I feel a trip to the Ady Lab coming. I will attempt to give the connection a clean . My double din is still working well and so are my exhaust and alloys. BTW I have put "Greeny" on EBay.

Simon, I didn't realise you had to have mph to pass the MOT. I hope I haven't got one of those dodgy MOTs mentioned elsewhere.

[Simon Jones]

I concede that I may be wrong about the MOT side of things. However, I'm sure it always used to be part of the SVA test when importing a vehicle to the UK

See Section 7 in this doc http://www.direct.gov.uk/prod_consum_dg ... 199220.pdf

"7 What is Type Approval?
We need to know that a vehicle is properly designed and built, and that it meets environmental standards. This is a legal requirement before a vehicle can be registered and taxed. We call the process of confirming this ‘Type Approval’.
You must produce one of the following to provide evidence of Type Approval.
- A Certificate of Conformity
- For UK registration, if you have an original European Certificate of Conformity it will need to state that the speedometer shows miles per hour (imperial units) and that the vehicle is suitable for driving on the left-hand side of the road. If this is not stated then you will require additional approval."

To get back to the original issue, I'll take a look at the component on the back of the speedo circuit board to find out if is is voltage regular for the instrument panel. Will report back Monday evening.

[rita]

You raise a good point Ady: that speedo still shows KMH at the bottom which by rights should be an MOT failure, even if a chip has been fitted to reduce the reading to show MPH.

Hi Simon the MOT inspection only involves the following,it doesn't mention kph/mph

Method of Inspection
Reason for Rejection
This inspection applies to all vehicles first used on or after 01 October 1937.
If the dial glass is cracked, it is not a Reason for Rejection, providing:

there is no possibility of misreading the speedometer or

there is no possibility fouling of the indicator needle or

the cracked glass does not create a safety hazard.
A Tachograph is an acceptable alternative to a speedometer providing it satisfies the requirements of this inspection.
1.
Check that a speedometer is fitted.
2.
Check the condition of the speedometer.
3.
Check that the speedometer can be illuminated.
1.
Speedometer not fitted.
2.
Speedometer incomplete, clearly inoperative or the dial glass broken or missing.
3.
The speedometer cannot be illumin

[Simon Jones]

Thanks for the info Rita

Removed the component from the Mazda 636 instrument panel & looks to be a D667C which makes it an NPN transistor rather than a voltage regulator, so it probably does control the low fuel light.