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MG MGB Technical - Temperature Sender Question

My temperature sender has died. I know this because the gauge is not working. I disconnected the wire at the sender, grounded it and the gauge showed full deflection to hot.

I recently had the engine out and repainted it. I removed the sender while I painted it. When I replaced the sender, I put sealant on the threads. Thinking that the sealant may have formed an electrical insulator, I removed the sender, cleaned the threads and reinstalled it. I used an ohmmeter to verify that there is conductivity between the block and the brass sender body. Still nothing on the gauge.

So my sender is dead. No biggie. However, my car is a 1970 roadster with a 1965 18GB engine. The Moss catalog shows only two senders, one for 1968-1974 and another for 1975-1980.

It occurs to me that the sender must match the block for physical characteristics, such as size and thread. It must match the gauge for electrical characteristics, such as the range of resistance it presents for different temperatures.

I was under the impression that this was one of the things that didn't change throughout the years. So should I use the 1968-74 sender, which would electrically match my 1970 gauge, or should I try to find a sender for an 18GB engine. If the latter, where would I find one, since neither Moss nor VB list one? Will the 68-74 sender physically fit into the 18GB cylinder head?
Paul Noble

Paul: I do not know if the 68-74 sender fits the older head, but I would have to believe that it would be a standard BSF thread pitch, and be the same as the older mech. gauge fitting.
In any event I would use a sender that matches the gauge you use. They are a made for each other. As long as the sender protrudes into the head and is "bathed" in hot coolant it should function correctly.
Andrew Blackley

Hello Paul;
Here the story as I remmember it. The threads in the head never changed thus everything interchanges. The 75 cars ran hotter and the factory relized that it would not look good to cust to have the gauge read higher so they came out with a recalibrated sender. On the midget they had the same problem only they actually were over heating. They had a recall and among other things they went to a recalbrated machanical gauge. In 76 they went to a large radiator. In other words don't make it run cooler, Just make the customer think so! Bob Thompson
Bob Thompson

Check out the great electrical information on the following website:
http://www.mgbexperience.com/electrical/temp.html

Lots of great MGB information on the main site, with TONS of excellent links...
http://www.mgbexperience.com/

Happy motoring...
Alan

Paul - The threads in all of the heads are the same (they would not be BSF threads as all MGBs went to ASE fasteners, but they might be 1/4 British Standard Pipe threads). Make your choice based on the electrical characteristics - probably the 68 - 74 sensor.
Good luck - Dave
David DuBois

The parts list differentiates between thermal transmitters for North America, Sweden and Germany on the one hand and elsewhere on the other, but only shows one part number for all years up to Sept 75, BMK 1644 in the case of North America etc. If you have an engine from a 65 it would have originally used the dual gauge, this changed for North America in 67 but not for the UK, but the parts list doesn't show different 18GB heads for the two markets, indicating the tapping remained the same. In 77 Triumph gauges were used (76 for the UK) so I suspect the characteristics of both sender and gauge changed. Go for the earlier sender.
Paul Hunt

That's what I thought. I didn't think that the physical characteristics of the sender changed over the years. While my engine is an 18GB (1965), the gauges and dashboard are all standard 1970 (Abingdon pillow) items.

I will use the one listed for 68-74. Its just that I had expected to see one from 1962, not 68 until the later years.
Paul Noble

As I say there wasn't a temperature sender until the 68 model year, before that it was the dual gauge, as shown in the Moss catalogue 'dash/instrument panel 1962-67'.
Paul Hunt

When Paul says dual gauge I think he is saying it is a mechanical temp gauge not electrical therefore no sending unit.
Leland Bradley

I couldn't figure out what you guys were saying about the dual gauge. There has to be *something* that screws into the cylinder head and relays information about the temparature to the gauge. Then I looked at the Moss catalog and saw that the temperature sender appears to be *included* with the dual gauge, at the end of a long cable of some sort that appears to be wire-wrapped or something. Its just that there is no *separate* sending unit. That is why the Moss catalog does not show one for years prior to 1968.

Now I understand.

Thanks for all the help, everybody.
Paul Noble

Paul;
The orginal gauges used a liquid carried through a tube to the gauge. The liquid expanded and moved the gauge needle directly. Cut the tube and you have ruined it. The wire wrapped around it keeps it from being kinked and protects it. Bob
Bob Thompson

This thread was discussed between 07/08/2002 and 12/08/2002

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