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MG MGB Technical - Temperature guage question

I have a 1977 MG "B" which I have owned for the past thirty years, and I have always wondered about the following. On the temp. guage, right in the middle are two very small white dots, a little bigger than the head of a pin. Are these dots a paint spatter or imperfection, or where they put there on purpose and what would that purpose be.
Thanks,
Donald E. Elliott
Noblesville, Indiana
DonaldElliott

The dots are used for calibration if you have the factory recomended calibration system.
John H

Donald,

all the electrical temp. gauges in the later B's do have this tiny marks on the instrument. Other cars that were fitted with the same gauges also have these 'dots' printed on at the same position.
I think it was printed there to help the instruments being tested during production by connecting the right voltage, adequate to the N - reading (~195°F).

Hope this helps

Ralph
Ralph

As Ralph and John say, they are for calibration.
If you look carefully at the speedo, there is a similar mark just below zero. This is where the needle should come to rest if you pull the stop pin back.

Very useful if ever you need the face off, or if you find that it is reading over, and you want to quickly move the needle back.
Martin Layton

Ralph

Any idea what temperatures the calibration marks correlate to? Also, am I correct in understanding you to say the the N mark should indicate ~195°F?

Thanks

Larry
72BGT
Larry Hallanger

They are very close to where the original Otter fan switch used to cut in on my V8, and that temperature is quoted as 90C/194F. However I have noticed that on the earlier gauges with temperature markings whilst straight down equates to about 185F, straight across i.e. H is 230F and half-way between them is about 210F. Whether this indicates my Otter switch was late in cutting in or not I don't know. I did replace it with the SU-Burlen item, which is physically different, and it now cuts in lower at about where 198 is on the Farenheit gauge, but it also stays on much longer sometimes until the temp gauge gets right back down to the N, which is much lower than the Otter switch used to cut out at.

Surely the N mark should be around the thermostat temp, which is nominally 82C/180F.

Paul Hunt 2

If memory serves, the "early" cars had the "N" at 180F (up to 1976).

The later cars, with electric fans (and different gauges) had the N as 185F.

The 77-79 Otter switch turned on the fans at ~195. They found this to be "late" so the 79-80 Otter switch turned them on at 185F. It also had the clip that made it less likely for the Otter switch to "blow out" under pressure!

M
Max Fulton

This thread was discussed between 23/08/2007 and 31/08/2007

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