Fried temperature sender - does this make sense?

[jules18375]

Engine 1.6TD JX

Symptoms - Has always managed to use lots of coolant. Header tank to coolant always full, expansion tank by number plate always empty. Sometimes the red flashing light came on by the temperature needle, topping up with more coolant seemed to make it go off. Did a few thousand miles last summer just feeding it coolant (about 1 litre per day when driving 200 miles). Seemed quite a lot! Garage cannot find any leak.

Then red flashing light kept flashing and couldn't make it turn off. Held temperature OK (needle at between 11 and 12 o;clock so all good). Have taken to garage to have cambelt changed and set about today to try to look into the coolant. Was planning on bleeding it, but nothing came out. No water, no air (I assume a couple of turns of the bleed valve is enough to open it up). Temp went up and up and radiator stayed stone cold all over. Turned engine off before I cooked it!

Now having a poke around, I think I've found the cause

engine 4_LI.jpg

Under this arrow (below the one you can see with the thin wire coming from it), coming off to the left is a temperature sender, the wires of which have become cooked and melted as they've been touching the engine. The wire is utterly fried.
My questions:
* Is this the correct sensor (found the part number on the wiki): https://www.justkampers.com/049-919-501 ... d-125.html and simply wire it in to the undamaged bit of the wire?
* When it is removed, will fluid come out? Any tips?
*Does this explain the red flashing light coming on (perhaps shorting on to the engine?) followed by no circulation of water to the radiator?

Any tips much appreciated. As you may guess I'm pretty rubbish mechanically but am trying to learn
Thanks
Jules

[Mocki]

I don’t "do" diesels, but ......

Firstly , that sender has nothing to do with the radiator being cold !
The flashing red light in the temp gauge has two functions ....
1. If the gauge is above 3/4 and it's flashing it means over heating
2. If the gauge is below 3/4 and it's flashing , it means low coolant in the header tank.

If it's say low coolant , and you can see the header tank is full to the brim ( not the number plate flap top up tank) then it's an electrical issue , and simple fault diagnostics will need to be employed !

Red flashing coolant light self tests when you switch the ignition on and then goes off ......

The system is very simple....
The headertank ( the one in the engine bay ) should always be full to the brim, and the top up tank ( behind the number plate flap) should be full to the max mark when cold. When the engine is up to normal running temp the coolant expands and is pushed into the top up tank, when the engine cools down the coolant is sucked back into the header tank
If this is not happening then you need to check the header tank cap , and the pipe between said cap and the top up tank .
If you are constantly loosing a large amount of coolant, either you have a leak somewhere ( radiator??? ) or head gasket issues , and at that point I’m "out" because inline engines are not my thing

[937carrera]

I "don't do diesels" either

Coolant usage with no sign of a leak tells me the coolant is disappearing down the exhaust.

No coolant when you came to bleed it, seems to support that theory.

Now if it was a spark ignition engine I know how I would easily test for a failed head gasket. Given it's a diesel, then I suggest you get a compression test done.

[kevtherev]

I "don't do diesels" either

Coolant usage with no sign of a leak tells me the coolant is disappearing down the exhaust.

No coolant when you came to bleed it, seems to support that theory.

Not quite.
A system leak when hot and under pressure onto a hot surface will evaporate.
Then when the engine is off and the coolant is cooler it shows no leaks.
This happened to me and was a bugger to find

[937carrera]

I agree, that can happen, but there are often witness marks, even easier to see if using pink G13 coolant.

Of course the other test method is to sniff the coolant for exhaust gases....... but more difficult to do when there's no coolant left

[jules18375]

Thanks for your comments.
Will it only allow me to bleed it when the pump is running? If the rad is the highest point, then surely coolant will only come out when it's being pumped around, or is just heating it up enough?
What does that fried bit do then - does it control when the pump comes on?
The fact that red lashing LED is on at low temps suggests coolant level. Maybe two faults then. Will diagnose as you suggest.

[kevtherev]

Thanks for your comments.
Will it only allow me to bleed it when the pump is running? If the rad is the highest point, then surely coolant will only come out when it's being pumped around, or is just heating it up enough?
What does that fried bit do then - does it control when the pump comes on?
The fact that red lashing LED is on at low temps suggests coolant level. Maybe two faults then. Will diagnose as you suggest.

The header cap actually increases the boiling point of your coolant by about 45 F (25 C). ... The boiling point of water increases when the water is placed under pressure. When the fluid in the cooling system heats up, it expands, causing the pressure to build up.
So as it gets hotter the leak will get worse.
The pump will move air to the highest points. (Header and radiator)
Some areas will need an air bleed screw to release trapped bubbles due to design.
The faster the pump runs the better it is at removing air

[ZsZ]

on "early" TDs with aluminium flange there are two senders in that position. One for the indicator and one for the glow plug system. The sender is the same as the one you linked.
on "late" systems with plastic flange there is one sender and its for the glow plug system, the other is moved to the side flange that has the hose that goes to the radiator.

[jules18375]

More fiddling around today. The red flashing light is now operating normally, i.e. flashing briefly on start up and then going off.
But the temperature needle just slowly rises and rises (until I get scared and turn engine off) and the radiator never gets hot. Interestingly, under the van, there seem to be two thick pipes going back to front maybe 35mm wide and these are cold, but two thinner ones, maybe 20mm and more of a flexible material, that are toasty and warm. I can also get hot air out of the heater matrix.

I've tried bleeding the rad, i've even had the bleed screw completely out, but still no signs of any air or coolant coming out of that. How can the heater get hot, but the radiator not?!

This is really confusing me.

And as for the fried sensor, leaving it disconnected, or reducing the resistance by connecting them together does nothing. Might it have blown a fuse somewhere if it shorted to the chassis? Anyone know which one?

Cheers

[937carrera]

Change the thermostat, it sounds as though it isn't opening at all which is why the pipes to the front are staying cold.

[kevtherev]

Take the thermostat out and pop it in a pan of boiling water
If it opens then your fault is elsewhere

[937carrera]

This might be useful - if the basic design is the same as the WBX the two small pipes you refer to are for the heater matrix, the flow to those is not affected by the thermostat

diesel_cooling.jpg

[Mocki]

I've tried bleeding the rad, i've even had the bleed screw completely out, but still no signs of any air or coolant coming out of that. How can the heater get hot, but the radiator not?!

This is really confusing me.

And as for the fried sensor, leaving it disconnected, or reducing the resistance by connecting them together does nothing. Might it have blown a fuse somewhere if it shorted to the chassis? Anyone know which one?

Cheers

ok i know i said im out, but

the heater is totally separate to the cooling radiator, and is supplied by those smaller front to back pipes which you describe as toasty warm.... the big pipes are to the main cooling rad.

i ts just a thought, but that fried wire and sender, it may be for glow plugs , and nothing to do with the gauges, but like i said i dont know diesels.

[jules18375]

Update:
Turned van around on drive (which is gently sloping) so that the nose was pointing down. Found that header tank wasn't as full as I thought and after a bit of fiddling around, revving, cap off, cap on etc I got lots more coolant in, so I think it was an air lock, not helped by trying to bleed with the radiator slightly raised. Anyway seems to be holding it's temperature now, in fact slightly lower than it was originally Radiator getting warm and big pipes under van now hot too.

The Dalek cap is knackered though - blows both way with ease so I need to replace that and then see where we are when it actually gets a bit pressurised.

Anyone know if this is the correct hose from expansion tank to header tank? I think I ought to replace that too

https://www.brickwerks.co.uk/brake-clut ... -blue.html" onclick="window.open(this.href);return false;

or can point me in the right direction if not!

i ts just a thought, but that fried wire and sender, it may be for glow plugs , and nothing to do with the gauges, but like i said i dont know diesels.

I think this is spot on and is completely unconnected (literally and metaphorically) What is it's purpose? Seems to run fine without it connected!