1.5 temperature sender / switch thread size

[Mikexx]

After changing my oil pressure switch which was permanently o/c I thought I would wire up the temperature sender with the VDO gauge.

However my conclusion was the temperature sender was actually a switch, from it also being o/c.

Does anyone know the thread dimensions of this for a BMC 1.5?

Also I like the idea of a gauge and a panic buzzer at the same time, but conscious the prices of temperature senders with integrated warning switches are rather high.

Has anyone looked into this for the 1.5 or other engine sizes?

 

[Tony Brooks]

If its a switch its distinctly non-standard. My guess its a faulty sender.

Before worrying about the thread you need to make sure the sender and your gauge match resistance wise. Get this wrong and the gauge will either read about twice or half what it should. I would advise you buy a matched pair sold as suitable for a BMC, then the thread will be right and the gauge and sender will be matched.

I am assuming this sender is in the SIDE of the thermostat cavity in the head. If its elsewhere it may be a switch.

[Mikexx]

20 minutes ago, Tony Brooks said:

If its a switch its distinctly non-standard. My guess its a faulty sender.

Before worrying about the thread you need to make sure the sender and your gauge match resistance wise. Get this wrong and the gauge will either read about twice or half what it should. I would advise you buy a matched pair sold as suitable for a BMC, then the thread will be right and the gauge and sender will be matched.

I am assuming this sender is in the SIDE of the thermostat cavity in the head. If its elsewhere it may be a switch.

 

Thanks, I was wondering how standard sensors might be? If the sender was fitted as standard rather than a switch, then I would have thought the VDO gauge would match?

As you say, the device is screwed into the head, just below the thermostat housing.

Currently the existing sensor is definitely o/c, hence my assumption it was a switch.

[Tony Brooks]

The question is do VDO gauges match the US or European standard. I am about 95% sure the BMC uses the European standard. The US senders tend to be thinner.

Study the gauges ad senders pages of the ASAP supplies catalogue.

[Mikexx]

4 hours ago, Tony Brooks said:

The question is do VDO gauges match the US or European standard. I am about 95% sure the BMC uses the European standard. The US senders tend to be thinner.

Study the gauges ad senders pages of the ASAP supplies catalogue.

I didn't know there were two standards. Thanks, its good to know.

The ASAP website page for senders:

  https://www.asap-supplies.com/gauges/senders-fittings/temperature-senders

doesn't suggest any fit the BMC engine. I do feel that recently ASAP are quietly removing BMC parts from their website, or perhaps just the parts I need!

[Tony Brooks]

Phone Calcutt Boats, I bet they will have a gauge & sender set to fit.

[Mikexx]

For reference, the thread is 5/8" 18tpi UNF.

[Rory123]

Would you know if a BMC1.8 temp sensor thread is 5/8" 18tpi UNF 2A or 3A?

Or does it matter?

 

Would this do the job? ... https://vdo-webshop.nl/en/temperature-sensors/410-vdo-coolant-temperature-sender-120c-5-8-18-unf-3a-4103590689641.html

 

[Tony Brooks]

48 minutes ago, Rory123 said:

Would you know if a BMC1.8 temp sensor thread is 5/8" 18tpi UNF 2A or 3A?

Or does it matter?

 

Would this do the job? ... https://vdo-webshop.nl/en/temperature-sensors/410-vdo-coolant-temperature-sender-120c-5-8-18-unf-3a-4103590689641.html

 

 

A bit late, but it depends upon the gauge matching the sender. The BMC is likely to use European standards, so if that sender is to US standards it will not be any good. They do give temperature V resistance data, so it should be possible to check. I think ASAP might publish that data on their website, but the OP still needs to know what standard his gauge was built to.

[Rory123]

Thanks Tony. 

I'm asking for my own boat...

 

I've a BMC 1.8 with a temp indication not working.

The sender resistance is about 1000 ohms even when the housing is too hot to touch. 

If I pull off the wire at the sender and touch it to  gnd, the needle on the dash goes full deflection so   I think the gauge and wiring is ok and So I think I need a new sender. 

 

Mikexx said above that it's a 5/8" 18tpi UNF thread and I assume it's european standard, but I'm not sure if the thread is 2A or 3A or if it matters. 

 

On the vdo website I found this one... https://vdo-webshop.nl/en/temperature-sensors/410-vdo-coolant-temperature-sender-120c-5-8-18-unf-3a-4103590689641.html

 

Then also list a 2A version. 

 

I think 2A/3A is to do with the tightness of the fit, but I don't know which one I need for a BMC1.8/Thornycroft 108??

 

Rory

 

 

[Tony Brooks]

Have a look here: https://www.asap-supplies.com/gauges/senders-fittings/temperature-senders

 

But unless you know if the gauge is built to USA or European resistance, you may well still buy the wrong one so it reads about half or double what it should. If the gauge looks "original", so possibly made by Smiths, it is probably a European one.

 

I have never heard of 2A and 3A and doubt it is tightness of fit, why not ask VDO. It just might be related to how many gauges it can drive, but I doubt it, or possibly the angle fo the seat at the bottom of the thread. Strange mix of dimensions - a diameter given on mm and an imperial thread size.

[Jen-in-Wellies]

2 hours ago, Tony Brooks said:

I have never heard of 2A and 3A and doubt it is tightness of fit,

Neither had I. Apparently it is a tolerance on UNC male threads. https://wilsongarner.com/the-difference-between-2a-and-3a-threads-threads-part-2/

 

[Tony Brooks]

I bet either will fit and seal, especially as I recall the BMC sender has a taper seat.

[Rory123]

The gauge does look origial and is labelled VDO and Thornycroft so I'd be fairly sure it's European. 

 

I'll order that one so and keep my fingers crossed. 

 

To fit it, so I just need a spanner? And ptfe tape?

 

I've emailed vdo too so will see what they say. 

 

Thanks for all your help. 

Rory