Td5 Temp Gauge and Sender - A Discovery

[ThreePointFive]

I know this has been asked countless times, but I am just looking to double check the collective experience of the forum and raise something of an issue to people that might not be aware.

My current setup is a TD5 tempature gauge with wiring directly to the green top (AMR1425) sender that came with the V8.

For reasons I don't want to go into, I recently discovered the gauge will not go beyond halfway in any situation. This makes it pointless, but also potentially catastrophic. Research confirms that TD5 temp guages are meant to be driven through the speedo, with a different 'curve' than the direct connection gives and hence the wrong display.

I am convinced by this event to get a real gauge which shows actual temperature, so I want to change,  I also want to make sure whatever I get works.

I wish VDO made white needled gauges in the TD5 style, but they don't, so I have to settle for orange unless anyone is aware of any. My alternative is to use the guage out of the original 1988-era binnacle, but this is also the 'cold/normal/hot' style, which I don't want. Aesthetic preferences aside, is there any reason why this gauge and this sender will not work properly in the Rover V8?

I can't see a way that the gauge/sender will not work, hot water is hot water no matter what engine it's in, but I am sure I can find the one exception to this which ruins everything.

Thoughts/comments welcomed.

[western]

I have that gauge & it's matching 5/8 unf sender in my 200Tdi, gauge directly connected to sender, it works fine. 

[landroversforever]

Mine was connected directly too, it’s the td5 fuel gauge that’s smoothed if I remember correctly. Is it the correct sender? It’s the 300tdi one you want. 

[Landrovernuts]

I binned my TD5 temperature gauge along time ago because as you have found and even when driven by the speedo doesn’t tell you the actual temperature until it is too late! The gauge has a huge dead band at mid way so doesn’t move until about 110 deg and then shoots up! 
I use VDO gauges now - although not the one from your link and they work well. You need to keep the existing sender and wiring though for the ECU. 
I used the original pipe on the head and welded a boss to fit the new additional sender. I did try a new Britpart stub pipe but found it was porous - original was much chunkier!! 
 

Toby

[Retroanaconda]

Lot of talk at crossed purposes here.

Any aftermarket gauge and matched sender will work, so long as the thread is correct. A VDO one like what you have link will be good and pretty accurate. I would go that way.

The Td5 temperature gauge is driven by the ECU on Td5 vehicles. On non-Td5 vehicles (factory ROW-spec 300Tdis or any other engine) the signal from the sender has to be fed via the speedo head. This is not for damping, but to adjust the signal so the needle sits correctly. It will work without it but the needle will sit in a different position at ‘normal’ temperature.

The Td5 gauge, like all factory car temperature gauges, is designed not to move during normal engine temperature variations, because most people will be worried by a moving gauge. 

[ThreePointFive]

Yeah that's a much better explanation.

The upshot is that the current gauge in any form wouldn't give me useful information, so I've already purchased the one above. Knowing the actual temperature is going to be far more beneficial, and I can check its calibration against the measquirt readings.

 

[Escape]

2 hours ago, Retroanaconda said:

The Td5 gauge, like all modern factory car temperature gauges, is designed not to move during normal engine temperature variations, because most people will be worried by a moving gauge. 

FTFY 😉

Never thought I'd be calling a Defender modern, even if it is a TD5. On my classic cars, I can tell when the thermostat opens as the needle will drop a bit and then rise again and stabilise.

[ThreePointFive]

Because it never fking ends, I have fitted my new temp gauge and sender..... but it doesn't work.

The ECU is reporting normal temperates while the gauge sits at just below 40 degrees. The + and S (signal?) terminals on my 2002MY wiring harness had to be swapped around to match the markings on the rear.

With the positive and S terminals attached but no negative, the gauge will sweep beyond the 120 mark and stay there regardless of engine temperature. With the earth, it sits at 40.

I've tried swappingthe + and S connectors back (opposite of what the markings want), but it just doesn't work, which I see as a good thing.

I'm thinking either this sender is not matched, or there is a problem in the gauge.

Any thoughts?

 

[ThreePointFive]

Because INFE (see above), this continues.

I have finally been able to get the sender out and replace with a standard temporary one (threw my old one away when fitting new, like an idiot). The sender is the correct part number for the gauge, so there's no obvious win there.

I have been given a table to check the resistance against by chucking it in a cup of just-boiled water.

I think it's roughly where it should be, which is not what I wanted to find out.

Is there any easy way to test te gauge isn't at fault? I'm thinking of rigging a very simple circuit up to the alternator but it's effort and I don't know if there's any easy way to check that others know?

[FridgeFreezer]

You can short the gauge sense pin to ground to prove the needle moves, you can also stick resistors of known values from ground to the sense pin to see if it reads correctly - if you need a selection of resistors posting I'm sure I can sort you out a handfull if you let me know the values.

[ThreePointFive]

Legend. I have shorted it and the needle does move, so now need to work on the temp being displayed.

Explain like I'm five, though - what's the best selection of values? 38.47 ohms is 100c and 50 is 197.29, would that be enough?

 

[FridgeFreezer]

1 hour ago, ThreePointFive said:

Explain like I'm five, though - what's the best selection of values? 38.47 ohms is 100c and 50 is 197.29, would that be enough?

Standard values close to that are 39 and 200, I'll see what I've got and pop a selection in the post.

[pete3000]

I did the td5 dash speedo conversion a while back, the temp and fuel gauge didn't work correctly and sat at half way as someone mentioned above. I concluded the drive from the speedo head despite being wired up for ROW spec was duff. The speedo works fine however. I believe the td5 gauges work on PWM drive as I couldn't get much movement by shorting to + or -.

I got a vdo vision temp gauge and sender which is nicely accurate in degrees c. The fuel gauge is taken care of with the td5 gauge and a gauge wizard from Spyda. This can be calibrated for fuel gauges/senders and other senders/gauges. A bonus was the output for the fuel low light which you can calibrate to flash at an even lower level to warn you of an impending walk.

Edited March 28 by pete3000

[ThreePointFive]

I changed the complete set to TD5 ones, speedo is correct and the fuel gauge is reasonably accurate so I haven't needed to modify that.

You may have just pointed out my problem then - I didn't realise the temp gauge went through the speedo, I thought it was a straight positive feed. 

So in short, I need to put in a new 12v feed from the fuse box and see if that solves it. 

Fridge, hold off on the resistors...

[Sigi_H]

I have never worked with this topic, but as an electronics engineer I would attach importance to a stabilised voltage. Isn't there a stabiliser in the dashboard? Is it connected to this circuit?
I would first feed a defined current into the display to check the gauge and then check the stabiliser if one is involved.

[pete3000]

The 12v and 0v for the gauges come from the loom on pin 1 and 2 not the speedo. My point was the drive signal for these comes from the td5 speedo as a pwm signal. See

http://www.retroanaconda.com/landrover/gauges_diagram.pdf

The fuel and temp sender inputs go straight into the speedo. If you want to keep your resistance 300tdi water temp gauge you'd need to break the red sender wire into plug B pin 5 and coming out of plug B pin 9 as pwm shown and use the dotted red wire.

Fuel sender goes into speedo plug B pin 3 and comes out as pwm onPlug B pin 7 to use the Td5 PWM gauge. There is also an output on plug B pin 1 to wire into the low fuel light.

neither of the gauge drive circuits worked on mine but the speedo did.....

 

[ThreePointFive]

Now sorted. I did still have a feed coming through the speedo, I hadn't looked closely enough at the wiring diagram to see it goes out on the 'S' wire via the speedo, not in on the positive feed. In retrospect that makes a lot of sense. Bypassing that part of the loom went straight to the sender, and it immediately worked.

But the point of posting this remains, if you have a TD5 gauge conversion wired 'properly' you'll never get a real temperature reading. It'll look like you do, which only makes it worse.

Interestingly my car runs cold a lot of the time, somewhere arount 78 degrees. I have the 76 degree thermostat, which seems a bit low now. Of course it does get up to 90ish when off roading or idling, but generally runs much lower. I'll need to modify my warm up enrichment in Megasquirt to ensure it's not over fueling, but I know these engines are meant to run in the mid 80s-90s more happily and this is a bit low.

[FridgeFreezer]

11 hours ago, ThreePointFive said:

Interestingly my car runs cold a lot of the time, somewhere arount 78 degrees. I have the 76 degree thermostat, which seems a bit low now. Of course it does get up to 90ish when off roading or idling, but generally runs much lower. I'll need to modify my warm up enrichment in Megasquirt to ensure it's not over fueling, but I know these engines are meant to run in the mid 80s-90s more happily and this is a bit low.

Well a 76 degree stat would certainly cause that - it likely won't be open fully until ~82deg anyway.