Temp Gauge wiring

[Sid Charles]

Hiya Guys

 

I have asked about this on the 12 volt boating group but what was suggested didn't fix it. When I got this old wreck I preserved the wiring or what was left of it, I did drawings so that I could see what went where, so having virtually completed everything electrical (some help came from you nice folk) well this one is really puzzling me, I still had the old Lucas Temp gauge, so I wired it just as it came to me, but it didn't work and I really thought it was the sender which is situated on top of the thermostat housing, this being a late 70s car engine (Peugeot 504/Ford Granada MK2) it is not difficult to find replacement sender on eBay or even Amazon, so I purchased one that looked as close as the original, I connected all the wires but nothing showed on the gauge, so I bought a new gauge and still nothing, and I was getting the engine real hot, I questioned my wiring but it not only matched what was on the boat originally, but it was as the gauge manufacturer said in the install leaflet, I then bought another sender thinking I may have the wrong one, but nothing, then I re-introduced the old sender and it still didn't register, I did continuity tests on the wiring and even rigged it up on a temp basis, and tried it on the bench by warming the sender, but the gauge never moved, So it must be me! what on earth am I missing? HELP

[David Mack]

Have you checked that the thermostat housing the sender is screwed into is properly earthed to the hull?

Also, my understanding is that there are two standards for temperature gauges - European and American. As long as both sender and gauge are of the same type, even if from different manufacturers it should all work. If you mix the standards it should still work but  you will get incorrect readings.

[Jen-in-Wellies]

When you say doesn't work, what does the needle do? Stay on the cold side peg, move to the overheated side peg? 

Have you checked the tempersture sender on the engine? Put a multimeter between the pin on the sender and a shiny bit of metal on the engine and give us resistance readings, engine cold and engine warm. Do this with the wire to the gauge disconnected from the sender. 

[Sid Charles]

12 minutes ago, David Mack said:

Have you checked that the thermostat housing the sender is screwed into is properly earthed to the hull?

Also, my understanding is that there are two standards for temperature gauges - European and American. As long as both sender and gauge are of the same type, even if from different manufacturers it should all work. If you mix the standards it should still work but  you will get incorrect readings.

Yep done that

2 minutes ago, Jen-in-Wellies said:

When you say doesn't work, what does the needle do? Stay on the cold side peg, move to the overheated side peg? 

Have you checked the tempersture sender on the engine? Put a multimeter between the pin on the sender and a shiny bit of metal on the engine and give us resistance readings, engine cold and engine warm. Do this with the wire to the gauge disconnected from the sender. 

I haven't checked a resistance like that but with 3 different senders they can't all be wrong?

[Tony Brooks]

This could well be a thermal or bi-metalic gauge and they only have two wires on them PLUS a voltage stabiliser in the positive feed. Mixing any part of that setup with modern bits is very unlikely to work.

 

 

Re David's post, mixing sender and gauge standards is likely OT get very roughly either half or double the expected reading, but the gauge should read something.

 

Edited to add - did it ever work, and how much of the wiring have you replaced. If a voltage stabiliser is involved then a multimeter is unlikely to set it "stabilising" but the load from both coils on a bi-coil gauge may keep it open circuit - long time since I dealt with these gages.

 

Edited March 29 by Tony Brooks

[Sid Charles]

On both the gauges old and new, if I connect a battery to pos and neg the needle shoots right over, don't like to do things like that, but it does prove there's some form of life

[Tony Brooks]

12 minutes ago, Sid Charles said:

On both the gauges old and new, if I connect a battery to pos and neg the needle shoots right over, don't like to do things like that, but it does prove there's some form of life

 

See my addition to my last post.

 

That is what it should do and it won't do a bi-coil gauge any damage.

 

The negative comes from another coil that pulls the needle away maximum deflection. The needle is normally held between two electromagnets.  A fixed strength one that connects to negative and a variable strength one that connects to the sender, the sender varies the resistance to alter the magnet's pull.

 

So no variable magnet pull = open circuit between the gauge and battery negative.

 

Is your thermostat housing plastic by any chance (thanks for the prompt David). If so the sender needs a pos. and neg. terminal.

 

Could you have made a terminal crimp onto cable insulation rather than the conductors. Try dabbing the sender terminal onto clean engine metal and telling us what the gage does. No harm will come from it, the electromagnet in the gauge limits the maximum current.

Edited March 29 by Tony Brooks

[Sid Charles]

Tony, I tested crimps and each wire and the housing is metal and is grounded to the hull

[Tony Brooks]

7 minutes ago, Sid Charles said:

Tony, I tested crimps and each wire and the housing is metal and is grounded to the hull

 

Then it has to be Jen's resistance check in case the sender is open circuit.

 

This may help with the sender identification. 

 

NSTRUMENT SENDERS

 

Oil pressure US standard 240 Ohms @ 0 psi > 33 Ohms @ max pressure

Oil pressure European 10 Ohms @ 0 psi > 180 ohms @ max pressure

 

NOTE: The above only applies to modern senders – some older ones “pulse” the signal

 

 

Temperature US Standard 450 Ohms @ 100F > 30 Ohms @ 250F

Temperature European 280 Ohms @ 40C > 22 Ohms @ 120C

[Tony Brooks]

A further thought. It is not uncommon for electric fan switches to screw into the thermostat housing. You said "looked the same", and if it is a fa switch then t would be open circuit until perhaps 90C and not close at a boat engine's normal running temperature. that would ft your symptoms.

[Tony Brooks]

As above but the thing that screws in could be an overheat sensor for a warning lamp/buzzer, and that would also give an open circuit at normal running temperature.

[Quattrodave]

16 hours ago, Sid Charles said:

Tony, I tested crimps and each wire and the housing is metal and is grounded to the hull

 

Hull?? Why are you grounding to the hull? Use an engine ground.

[Tony Brooks]

5 minutes ago, Quattrodave said:

 

Hull?? Why are you grounding to the hull? Use an engine ground.

 

True, but if the engine is not grounded to the hull then unless it has an insulated return starter, which seems unlikely to me, it would not have started, so he could not get it hot like he says he did. Even if there is no engine to hull negative bond I would have thought the control cables and exhaust should provide a sufficient return path for the gauge.  Also, with no such bond and an earth return alternator (as most seem to be) I would expect a running engine to make the charge light illuminate as the alternator back feeds from the field diodes to try to charge the battery via the warning lamp.

[Sid Charles]

Apologies to everyone, it was me! What a plonker I am, I have spent hours with wires strewn everywhere, tearing my hair out, all the questions and all your answers. So after work today at around 1pm I first did a resistance test on all 3 senders and I couldn't get a value on any of them, my test meter is Ok it is a RS Components one and I have used it loads for my work, so that was disappointing to begin with, so I went and sat next to the engine and replaced the old sender that the boat had when I bought it, I warmed the engine up hoping that a miracle would happen, but no still not a flutter on the gauge, then I re-introduced the old Lucas one and still nothing, so I thought I would try something that someone had suggested and removed the negative wire from the gauge because it should make the circuit through the sender to the engine, and that made no difference, I then extended the wiring so that I had the gauge in my hand whilst I sat puzzling, I swapped the wires around knowing they were right , but you never know, IT WAS AT THAT MOMENT THE LIGHTBULB CAME ON, I looked across at the domestic battery isolator and realised that during my frantic attempts to solve this I had taken my positive feed from a small positive busbar in my switch panel and the feed from the batteries was OFF, you see I intended running a decent cable from the starter battery to feed the gauge but I forgot, so the positive feed was still coming via the domestic bank which was switched to OFF, I knew straight away, I stood up leaned over and turned the isolator to ON, I could have cried the gauge flicked straight over to just under 90 degrees, I sat with my head in my hands for a few moments as I  realised I had only taken the positive as a temporary because the actual feed comes from the ignition key and the red wire which was sticking out when I bought the boat is actually the feed to the gauges in a sort of daisy chain, trouble is that cable is not in the round trunking from the ignition, so tomorrow I have some 10 mm split conduit and the red wire can go in that. I really am sorry for all that, it was one of the biggest blonde moments I have ever had lasting 3 days or more, sorry sorry sorry and thank everyone of you, all your suggestions were valid...I'm going for lie down in a dark room.

[Alan de Enfield]

 

As a wise man once said ...................

 

"The man that never made a mistake, never made anything !"

[David Mack]

And there was me suggesting the negative connection might be bad when the positive was the problem all along.

Glad you've got it sorted!

[Tony Brooks]

Me also.

[Sid Charles]

Thank you all, I feel so foolish

[ditchcrawler]

11 minutes ago, Sid Charles said:

Thank you all, I feel so foolish

Not at all, especially as you came back and told us what the problem turned out to be 

[Tony Brooks]

26 minutes ago, Sid Charles said:

Thank you all, I feel so foolish

 

I bet we have all had moments like that. I just published 80 amps when it was clear from the text I meant Ah. No idea how that happened.