[Mgs] Jaeger Dual Gauge Modern Replacement Accuracy & Calibration

[Robert's New iPad]

   I did not read this thread from its beginning, thus my comments may be off target.
   My assumption is that Bob put the bulb into a pan of boiling water, at which time the gauge indicated 190F.  Unless he is testing about about 8500 ft altitude, that 190F is low.   If he tested in boiling water near sea level,  Paul is spot on-it is an out-of-spec gauge.
   That is a good way to test gauges and thermostats, adjusting for altitude. 
   It seems to me that contents of the tube alongside the engine’s head are already gaseous, thus heat added from the head would have insignificant effect on the gauge reading. 
  I infer that the vendor is not offering to replace the gauge.  If Bob wants to keep it and to install it, the infrared thermometer would allow him to chart the difference between gauge reading and thermometer ready, hoping that the error is linear.
  But then, there remains uncertainty about accuracy the oil pressure half of the gauge....
Bob


> On Jul 20, 2020, at 11:28 AM, PaulHunt73 <paulhunt73 at virginmedia.com> wrote:
> 
> No you aren't, and they would say that as it's obviously their gauge that is faulty.  Installed I can't see cooling system pressure squeezing the bulb enough to boost the gas pressure and hence the gauge reading anywhere near 20 degrees.  I don't know the correlation between pressure and reading, but it may be similar to the oil section. 
>  
> I have often wondered whether the long (in an MGB at any rate) capillary tube being alongside the head in the engine compartment does add a little to the reading, as all the tube there could be at 100-plus degrees F in hot weather compared to less than 30 degrees in very cold weather, with the bulb - presumably with a correctly working stat - being at 180F in both cases.
>  
> If you were in the UK I'd say demand your money back as it's not fit for purpose, there are consumer protection rules, less easy if you are in another country.  So many people these days just moan and don't demand corrective action, so there is little incentive for suppliers to up their game.  The simplest thing is to be aware of it, and take the same action when it reads 190 that you would at 212.  Moving the needle could cause damage, but there may well be some negative reading that the stop prevents that would mean it wouldn't be 20 degrees off the stop when cold.  To me though, it would be more irritating to see that, than taking account of known under-reading, as I find in both my cars there can be significant differences in 'normal' running winter and summer'.  Unlike modern cars which I believe are computer controlled to prevent owner paranoia with 'normal' variations.
>  
> PaulH.
>  
>  
> ----- Original Message -----
> I bought a new "Jaeger" dual gauge for my MGA  from a vendor in England.  ...  The new gauge never got over a hairs width beyond 190.
> 
> I called the vendor and they intimated that I was crazy to test it the way I did.  Am I?  Is there a better way to test it without installing it?  Or is installation and an infrared thermometer a preferable way to test it.
> 
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