'85 TE - Thermal trip relay - how to test?

[thebartman]

I have noticed the water temp rising above normal, so have decided to ensure cooling is permanently sorted.

I have replaced the sender unit in the water pipe in the boot  ( you know, the one that runs above the Alternator  !!!) and this works.

I have a replacement Otter Switch - which I have tested with boiling water - and this works, though not replaced yet until my wire pliers arrive Friday..

The last item to test is the Otter Thermal Trip relay. - The black box with red plunger.

How do I test this unit to check the relay is working correctly?

 

 

[910Esprit]

I'm speculating here...   As long as the positive feed to the fan is +12ve, I assume its working from a cooling system point of view?   

Presumably if you 'ground' the positive feed to the fan, the button should pop up?    (I think its purpose is as a failsafe if a fan motor seizes or otherwise fails).

If it disintegrates as part of such a test, I guess its not working 😀  

Edited March 30, 2022 by 910Esprit

[Escape]

If working correctly, there should be no resistance across the terminals, so the fan gets all the power. If it trips, the connection should be open (infinite resistance).

[thebartman]

Thanks chaps - (It's not yet disintegrated !!)

So the plunger is "up". and it does not seem to reset.

Does it need power to do this, and if so where is it supplied from? I'm not good enough yet ( 😞 ) to fully comprehend the wiring diagram ...

 

[910Esprit]

Just checked - Mine is just spring loaded too and stays in the 'up' position.   So my original assumption about 'popping up' cannot be right!

[thebartman]

Just for completetion .....

I have replaced the Otter Switch  - underneath the RHS (Drivers side) front wheel ( and wire-tied) . Connectors disintegrated but also replaced by newly crimped terminals.

When the engine gets "up to temp" the fans don't seem to come on. I am using an IR thermometer - but measuring the alloy pipe next to the new Otter switch it only reads 75 deg C, whilst temp sender in cabin reads 90+ deg C. Is this OK/normal ? Is there a thermal co-effieciant (water vs. pipe) going on? 

Fans don't start when apparently reaching temp - however, when I switch the "Aircon switch" to ON, all 3 fans burst into life and cooling happens just like it says in the fairy stories !!

So I now have cooling via another switch - but why do I have to force the issue by switching the aircon switch on - why doesn't the Otter switch just kick in and start the fans?

Apologies to those who know about this stuff - but I would like to know how this all hangs together ...

 

[Sparky]

A/C commanding all fans on is a good sign.  IR thermometers will give various readings depending on the target substance composition and albedo.  Your temperature gauge may not be entirely accurate.  The value of your investment may go down as well as up.

[thebartman]

14 minutes ago, Sparky said:

A/C commanding all fans on is a good sign

Excellent - thx.

14 minutes ago, Sparky said:

IR thermometers will give various readings depending on the target substance composition

Which was why I was asking about thermal co-efficients ...

 

15 minutes ago, Sparky said:

Your temperature gauge may not be entirely accurate ..  It's always down

It' a 1985 Lotus Turbo Esprit !!!!

But I have a brand new, tested , temp sender.

 

15 minutes ago, Sparky said:

The value of your investment may go down as well as up.

It's always down - down down, deeper and down ..... ( and what is UP! ?)

🤣

[Sparky]

Ah, but do you have a brand new, calibrated temp gauge?  Up:  your blood pressure?

BTW, those thermal trips are always in the same position, visibly.  But when it has tripped, you'll feel it click when you press it.

[thebartman]

I love the forum ....  🥰   😇    🤣

Cheers @Sparky

 

[Escape]

Have you tried bypassing the OTTER switch? Just put both connectors together or use a jumper to bridge the pins on the switch (with both connectors in place). With ignition on, the fans should start turning. if they don't the problem is in the wiring between the OTTER switch and the fan relay.

As above, the fact you can get the fans to work with the AC means the problem can't be too serious.

[Sparky]

My toolkit contains a little jumper lead for precisely this purpose.

[Escape]

7 hours ago, Sparky said:

My toolkit contains a little jumper lead for precisely this purpose.

So does mine! 🙂 To be precise, I carry a few short pieces of stiff insulated electrical cable, with both ends stripped and flattened with a hammer, so they fit perfectly in a female spade connector (or a relay base, if you put both flats at 90°). Comes in very handy!

[snowrx]

I could see the gauge (@engine) sender being at 90 while the Otter switch at the other end of the car is 75, at least while it warmed up before the thermostat opened. If your IR thermometer is giving weird readings on a shiny cooling pipe you might find a cheap Digital voltmeter that comes with a K-type thermocouple that you could touch to the pipe. What temp is the otter supposed to close on?

My Federal '85 has the Otter switch in the tube that goes over the alternator, maybe to respond just a bit sooner?

I would guess the thermal trip is a bi-metallic strip heated by the current running through it, so running significantly more current than the fans normally draw should open the switch, and the button manually resets it, perhaps after it cools.  If you have an ammeter and some 12VDC loads, you might be able to get a sense of where (or if!) it trips.

 

[thebartman]

Thanks @snowrx - where your Otter switch is located seems to be the place where my (DOM) temp sender unit lives.

14 hours ago, snowrx said:

could see the gauge (@engine) sender being at 90 while the Otter switch at the other end of the car is 75, at least while it warmed up before the thermostat opened.

Absolutely - I measured this at 85deg C whilst the cabin guage was working its way the past "90" line toward the next line on the guage - so I bottled out- rans the fans thro' the AC switch then shutdown for the day.

14 hours ago, snowrx said:

I would guess the thermal trip is a bi-metallic strip heated by the current running through it, so running significantly more current than the fans normally draw should open the switch, and the button manually resets it, perhaps after it cools.  If you have an ammeter and some 12VDC loads, you might be able to get a sense of where (or if!) it trips.

I have a 12VDC power source, clips/cables etc. and this was my original intention - how to test if it actually works. Thanks for your input - when the rain showers stop and I get a mo - I shall try your suggestions - with increasing amounts of current until it trips (or not!).

Having replace the Otter switch (82-92 deg C) I might just invest in a 72-82? (Hot Climate version) so that the fans start cooling at a lower temp at the rads, but the proper temp for water arriving back at the block.