Temperature gauge not working - diagnosis

[JeremyC]

I'm teetering on the edge of buying a low mileage early F. The temperature gauge is not working and I understand this is most likely the sensor which is a one wire sensor and if I touch the wire to ground I should get a maximum temperature reading. If it's the sensor I'm happy to go ahead with the purchase, if it's gauge or wiring I might have to think a bit more.

My question is can I get to the sensor to do the grounding test via the engine cover in the boot or do I need to go in via the cabin or from underneath.

Many thanks.

Jeremy

[mgtfnut]

Under the bolt on engine cover - from the top.
I can't remember offhand, but there are two sensors, one for the gauge, and one for the ECU. Both mounted on the elbow bolted to the cylinder head on the exit path of coolant from the head.

[Notanumber]

A quick search of this forums and the others will clarify which of the 2 temperature sensors it is. Nothing will explode if you ground the wrong one though and then try the other

[Rob Bell]

Changing the gauge in the instrument cluster isn't too difficult either, if it comes down to that...

Actually, another potential problem could be the loose printed circuit on the back of the instrument pack. If the instrument pack has been removed previously, it is possible to damage one of the copper lines. Fortunately, we're looking at late 80s/early 90s technology, so this is easy to recognise and potentially even repair with a blob of solder. Or you can simply swap it for another circuit...

[JeremyC]

Thanks folks, car now purchased. It's an early one, chassis number under 2000, supplied Feb 1996. I'm the third owner and it's done 42k.

I will get the engine cover off at the weekend and have a look. I'm using it for an Autosolo at Goodwood a week Sunday so it would be nice to have a working temperature gauge.

The oil temperature gauge is also misbehaving as it is only coming off the stop a little way. I suspected a sensor on this too but maybe it is gauge crustiness, it has only been used 700 miles in the last 7 years!!

I'm afraid I might be starting quite a few threads in the next few days (after searches of course).

[EllsoJo]

Thanks folks, car now purchased. It's an early one, chassis number under 2000, supplied Feb 1996. I'm the third owner and it's done 42k.

I will get the engine cover off at the weekend and have a look. I'm using it for an Autosolo at Goodwood a week Sunday so it would be nice to have a working temperature gauge.

The oil temperature gauge is also misbehaving as it is only coming off the stop a little way. I suspected a sensor on this too but maybe it is gauge crustiness, it has only been used 700 miles in the last 7 years!!

I'm afraid I might be starting quite a few threads in the next few days (after searches of course).

A low coolant alarm is IMO an ESSENTIAL piece of kit ESPECIALLY if you have ANY doubts about the effectiveness/reliability of coolant AND oil temp gauges!

I fitted a chap one which attaches to the outside of the expansion tank. QED to fit. I can find the details if you are interested.

[JeremyC]

Thanks, I intend to. Was it this kit? https://www.ebay.co.uk/itm/305053857329 Have you ever tested by deliberately removing some coolant.

Thanks.

[Charless]

The oil temperature seldom gets anywhere near the middle of the range unless you are really thrashing it - such as a very enthusiastic track day - so nothing to fix there. The water temp gauge should sit a notch under half way under all circumstances once warmed - your sender unit is the most likely culprit here. The blue or black sender on the underside of the engine elbow is 'easily' replaced without losing significant coolant as earlier advised. Traditionally the brown sender (ECU temperature input) is in the horizontal position at the same elbow but it wouldn't matter if their locations were twitched. The connectors are different so you can't mix them up.

[JeremyC]

Thanks, I plan to introduce myself to getting to the engine tomorrow, including identifying whether I need a blue or black sender.

Top priority tomorrow is preventing the petrol smell in the cabin. The engine bay smells fine so I suspect I just need to reseal the fuel pump access panel.

[Charless]

Early ones were blue, later ones black, but buy one from a reputable site and replace the blue or black one as found.
I doubt the pump access panel seal is the problem but good luck.

[EllsoJo]

Thanks, I intend to. Was it this kit? https://www.ebay.co.uk/itm/305053857329 Have you ever tested by deliberately removing some coolant.

Thanks.

Yes, that WAS the kit I used. The guy I purchased it from gave helpful advice (initially via Ebay's "Contact the Seller" system, as I recall.)

I chose to also have a warning light, wired in parallel with the buzzer. Pictures which (hopefully) explain what I did are attached. As I recall, the LED must be demand less than 30mA for the system to work. Check this "Fact" with seller to be on the safe side!

I DID test the system: I found that it was easier to clean the expansion bottle so that the sensor would stick, by undoing the mounting bolts (2??) and lift/tilt the bottle until I could reach all surfaces I needed to clean. Having stuck sensor on and wired-up, testing was just a question of tilting the bottle as far as I could, which was JUST enough to trigger the buzzer.

I have encountered a few false alarms: Accelerating hard up steep Devon hills seems to cause a brief buzzer sound. Strangely, the system is ONLY prone to F.A.s when everything really fully warmed - up. Hottest days last Summer after a longish run down to Dartmoor being a case-in-point.
I have now included a switch in the buzzer circuit ONLY, so that I can turn the buzzer OFF when my wife is aboard. I still see the warning light, but I do not get the buzzer amplified by wife droning for the next 10 minutes along the lines of "Why do you need that buzzer? --- drone drone"
By Murpy's law, I have never heard a false alarm since fitting the switch, even when the buzzer is switched in circuit. B.T.W. the buzzer & light work briefly, every time the ignition is turned on AND as the starter operates> I like that, but wife does not, if I have forgotten to throw the switch!
Hope this all helps. I had lots of help on another Forum (RoverLike is a STAR!) re what can and should NOT be done on the instrument circuit board etc.

[mgb281]

Another option and potentially a better one is this from an earlier thread, the reason it may be better is that it does away with the weak MG expansion tank; viewtopic.php?f=8&t=10757&p=201171&hili ... rm#p201171
These are available on Ebay from numerous VW, Audi, Skoda and Seat cars, make sure you get one with a blue not a black cap though. Also make sure it comes with a plug and at least a couple of inches of wire. For the alarm I used one of these, they are now back in stock by the seller; https://www.ebay.co.uk/itm/175946711884 ... R8joo53hYg due to having lost all high frequency hearing an alarm is useless for me but the seller also has an alarm that can be wired in. There is no need for a time delay due to the probe extending way down low, if you are cornering hard enough to trigger the alarm then low coolant will be the last of your worries. If you want a test button just wire in a press to break switch in the sensor circuit just as he does in his other alarm.

[Notanumber]

+1 A low level warning alarm will save your bacon more than the oil temperature gauge. It is claimed that hole in the dash was intended for an oil pressure gauge but this was dropped pre production due to the cost of a suitable oil pressure sender unit. A battery volt meter would probably have been of more use in that space.

[Notanumber]

Bruce Cotsell's alarm in Jermy's link is very good. Bruce is quite well known and is active on the T bar forum. I fitted one of his alarms to my 115 and then went back for a second one for my 135 Sunstorm.

On the second one Ive wired the buzzer through a variable delay circuit ( it was all of £ 3 on Ebay). It can be set between 1 and 10 seconds so Ive just set it about half way. This way it obviates the noisy bleep when starting the ignition and prevents any false alarms during hard cornering. If the level is consistently low for more than 5 seconds the buzzer will sound.

[JeremyC]

Thanks Notanumber, two very useful insights, I'll look out one of those delays.