crwoody

Deffo sounds to me like a head gasket failure. They can fail in different places, between different chambers/cavities. Yours sounds like it's failed between a combustion chamber and water jacket allowing combustion pressure into the the cooling system, the water pump doesn't really generate all that much pressure.

You should be able to tell by the sound of it if you set the alarm off, it's a fairly distinct, (though not all that loud,) sound compared to the feeble car horn noise if that's what's fitted. In any case you should observe the correct procedure for disconnecting the battery anyway. It should be in the handbook.

If the engine is not getting hot enough it would suggest to me that you may have a faulty (failed open) thermostat. There shouldn't be any significant flow of coolant through the radiator until the engine is hot enough to cause the 'stat to open, so whether you have a running fan or not should make little or no difference. The Td5 engine doesn't seem to generate much heat until it's being worked fairly hard, so in stop/start slow traffic conditions from a cold start, you won't get much heat out of it anyway. Maybe the Diesel heater idea as above would be a better solution.

Only 9.5V at the dipped headlights is very poor, where were you connecting the meter earth? I you have a secure ground connection, it's most likely a sign of the switch failing or possibly poor connections at the fuses. I would in any case add relays to take the filament current off the switch contacts for both dipped and main, I looked at adding relays in the dash myself but ended up taking the easier option of fitting a Boomslang loom instead and wired the power feed direct to the battery, (via a fuse,) rather than the alternator, it really makes little or no difference.

On all Td5 models, both head lights are wired from the stalk switch contacts but then split through separate fuses which is why they appear separately at the front, there are no relays on any of them. The commercially available wiring and relay looms are designed to take the connections to drive the relays from one side only, and then put out a parallel feed to both lights from the same relay, hence only 2 relays, one for dipped and one for main. The wiring as supplied is just long enough to reach with the relays mounted in the N/S inner wing behind the headlight. As for the light bar, a 30A fuse would be enough but I would be inclined to add a dedicated separate relay and switch.

Corrosion, wrong nuts fitted in the past, wear due to loose nuts?

I'm just using the original OEM aerial with a splitter, works well for me.

It should be on the front edge of the seat box, between the passenger seat and cubby box. It’s wiring goes through a grommet in the cover plate beneath the cubby box and disappears into the loom above the transfer box.

I would suggest that what you're seeing on the rev counter is the result of a (possible) problem rather than the cause, as with the crank sensor, if it works normally otherwise I'd say it's not at fault. Perhaps it's a switching glitch from the glow plug relay being activated? Has it only just started doing it? I added a rev counter to my Td5 90 (2004,) not a LR supplied one but from Smiths, https://www.smiths-instruments.co.uk/landrover It looks very similar to the original VDO one and connects the same, when I turn on the ignition, the needle goes to full-scale then returns to zero, some kind of self check thing I assume, I wonder if yours is doing something similar?

By a strange coincidence, I've just been looking at my crank sensor as mine is often slow to start, hot cold or otherwise, it will crank for some time before it fires but then runs perfectly fine, I am getting a "noisy crank signal" error on the Nanocom. Just for reference I checked the resistance between the signal wires at the ECU and found a resistance of 1.24KΩ which I would guess to be about right given the type of sensor. If the engine runs normally I wouldn't really expect the sensor to be failing, they usually either work properly or not at all, (about 1KΩ or open circuit,) and the engine won't run if it's failed. I find I can bump-start the engine if I'm parked on a slope and it starts immediately, so this suggests to me that the starter motor could be interfering with the signal, possibly due to sparking caused by worn brushes, or even a failing battery. It's also worth checking the security of the earth connections, battery to chassis/engine and the second one from chassis to engine near the starter.

Sounds to me like the "main relay" has failed, under the driver seatbox, it switches the power to the engine ECU when the ignition is turned on.

Why not get one cylinder to TDC and poke a sick down the glow plug hole to gauge the depth and compare with the length of the new ones. Maybe it's had the wrong ones fitted previously?

It will be the resistor pack for the fan speed control.

The later ones were fitted with Torx screws, earlier were #3 (I think) Philips heads. To be honest, you're better off undoing them with a spanner from behind and just use the screwdriver to try to stop the head from turning.

"defender td5 2011" ? "Turn the key and it's dead" - Any clicking noises? Do the ignition lights dim when trying to operate the starter? Possibly flat battery due to faulty alternator or even just broken belt, also backed up by battery light coming on first.

I’ve just got an amplified splitter on mine connected into the original OEM aerial lead, works well for me👍

There is a pressure sensor on the AC system, so I'm guessing that it would inhibit the clutch in the event of low refrigerant pressure, specially since the gas also carries the lubricant for the AC compressor. No gas = no oil = knackered pump.

I use a Nanocom Evo for my Td5 90 and Disco 2 for the engine ECU, ABS and alarm, I'm not so sure what use it would be on a 300Tdi though, other than for the 10AS. There might be a simpler/cheaper alternative for just the 10AS. I'm sure someone more knowledgeable will be along shortly.

Depending on year and configuration, if yours is 2002 onwards and is equipped with ABS, there should be a yellow/pink wire from ECU pin 19 going to the ABS unit that you could tap into.

The power to the ECU is linked to the inertia switch so as to kill the engine in the event of a crash, so yes it does need to be linked.

I fitted a pair of horns that I took off a VW Golf scrapper, I had to make a bracket for them to fit in place of the original single horn but well worth it. I also added a relay to switch the power directly from the battery. Just be aware that if you're fitting salvaged or new conventional horns, the back, (mounting screw) of the horn vibrates so they need to be mounted on a flexible strip to work properly, if you mount them onto a rigid surface or bracket, they won't sound at all well.

I wouldn't risk sunflower oil on my Stihl, I doubt that it's lubricating qualities are up to the job. If I had to use a substitute I had to hand temporarily, I'd use a heavy gear oil, EP90 for example. The proper stuff is sticky but also thixotropic, it sticks to the bar and chain without being thrown off by the centrifugal force

The indicator relay is designed to flash quickly in response to insufficient current being drawn on the circuit, usually caused by a failed bulb, if you're sure the bulbs are all OK I'd check on the earth returns from the indicator lamps, particularly the rear ones, it could be they're getting a return via the tail lamp filaments which wouldn't allow enough current to operate the relay properly.

I'm not 100% sure about the Puma models, but on the earlier Defenders that light is also linked to the handbrake switch, it's contact closes to ground when the lever is lifted, it could be that the switch it out of line or damaged or the wire is trapped somewhere and intermittently shorting.

There's only a single supply fuse for the 10AS unit, (fuse 7 under the seat box,) so if the immobiliser is working that suggests it's ok. Immobiliser, interior light control and central locking are all functions provided by the 10AS but it needs to be programmed accordingly, (via the OBD port,) they can lose their configuration or get corrupted, mostly I think due to the battery being disconnected, you'll need to find someone locally with a Nanocom or similar to set it up. I don't believe the spare connector has any bearing on the issue.