Series 1 V8 Temp gauge questions.....

Oldskoolrob

Active Member
Howdy - I'm not very electrically minded. The temp gauge in my S1 dash will sometimes fluctuate up into the uncomfortable zone. I've changed the sender unit in case it was earthing due to old age, but it's still happening. Last time I pulled straight over and the engine was definitely NOT overheating (a string of old Holdens has taught me what an overheating engine is like lol). So that leaves the gauge or wire at fault. I suspect that as the signal goes closer to earth the gauge indicates higher temperature? What's your esteemed guesses - faulty gauge or disintegrating wire allowing intermittent partial earth.......?
 
This is a stab in the dark. Do the oil pressure and fuel gauges if fitted fluctuate ?
I am not familiar with the S1 wiring, but usually these electrically operated gauges take their power through a voltage regulator, if the regulator either goes bad, or has a dodgy earth itself then problems occur.

I don't want to pee on your fireworks, but where did you source the new sender from ? The OEM sender would have been matched to the gauge in terms of resistance scale, in order to operate correctly a new sender would need to have the same values. In fairness though if you had a miss match then this would not usually result in a fluctuation, but more of an inaccurate reading.
It is a nightmare trying to get reliable electrical components these days. I always try to find an old OEM part if I need a sender or voltage regulator, taking them from a donor car.

You could make sure the temp gauge connections are tight. The gauge has a live supply, as said usually regulated, and its earth is through the sender into the engine, so taking the wire of the sender and touching it to the engine should see the gauge go right off the scale to max hot.

With a multimeter you could test the live wire to the gauge and see if the voltage is fluctuating. If the voltage is steady you could run a temporary new wire from gauge to sender to test and discount loom problems.

A hand held infra red temp reader is a handy thing to keep in a classic glove box, these take out the guess work with cooling issues.
 
Cheers cobraboy :). No need for fancy infra-red ray-gun: I figured if I could put my hand on the top hose and take off the radiator cap she's not overheating. :LOL:
I got the new sender unit from my local Land Rover mechanic. It's OEM so far as I know - It has the same part number but appears different (longer) But I did note that it reads slightly higher than the original so.......

rummaging through the shed I found a NOS auxillary/universal temp gauge so I might plug that in for a bit and see what it reads. Just to make sure it IS an electrical problem, I guess......??

Another thing I didn't mention is that the the fluctuations are slow - the needle doesn't jump around, it'll slide from 85 to red in about 2 seconds....does this mean anything to anyone?

One day my Rover will be reliable.....

One day.....

Surely.....
 
When I got my S2 v8 , in first couple of runs I thought the gauge was slow to rise, so I looked at the sender. Checking the voltage on the lead it seemed to be unstable, where its supposed to be stabilized on 10v - this is worth checking as it would indicate the stabilizer is failing. It should also affect other gauges, so watch them also. I find it difficult to look for erratic voltages on a Digital meter - one place where an old type of analogue gauge is better. In the end I replaced the sender and the thermostat, and the gauge readings now seem sensible - just below mid scale, decreasing if I run down a hill against the engine. On my Subaru with an OBD-II readout I can see real coolant temps fluctuate from 83-96C while the gauge does not move. Running downhill against the engine for < 1km I have seen the temp drop over 10C.
 
Yes, but a worn stabilizer may give fluctuating readings. A higher voltage may give the symptoms you are seeing.
 
Hi, Strictly speaking the gauge should see a steady 10v and the sender provides a varying resistance earth connection.

Both the voltage stabiliser and the gauge utilise a bi-metal strip which gives a slight variation of voltage and slow gauge response, it's just the nature of the beast. They are after all not precision instruments, which Harvey will and has stated on numerous occasions.

Colin
 
On my Subaru with an OBD-II readout I can see real coolant temps fluctuate from 83-96C while the gauge does not move. Running downhill against the engine for < 1km I have seen the temp drop over 10C.

This is common on modern cars where the gauges are driven by the ECU and not directly from the sensors. Volkswagens for example will almost always show 90°C as long as the ECU thinks the engine is in the normal temperature range.

Yours
Vern
 
When I worked at Land Rover the Range Rover temperature gauge was changed to give a stepped response, because drivers were concerned it was fluctuating up and down when driving especially off road, which was exactly what the temperature was doing. So instead of being a linear response it had a flat portion in the middle section where most of the variation was seen and then a steep climb at the overtemperature point.
 
Very common on modern cars. MX5 after ~95 do this, where before it was a true reading. The late gauges should be read as 'Cold...Normal...Head gasket'. There is an article on the web about how to fix this problem. Our 2009 Mazda3 is similar - gauge doesnt move while temp goes as high as 96C. There are very cheap ODB-II to Blue tooth senders on fleabay that talk to smart phone apps - like A$5.
 
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