This is because an infra red gun is measuring the radiation from the
surface not the temperature. The level of radiation is affected by the
colour. Dull and dark surfaces radiate more and shiny and light surfaces
less. Hence radiators, brake drums and the heat sinks on the back of your
hi-fi should be matt black and Thermos (vaccuum) bottles silver.
Dave Vodden
1992 Plus4
Hampshire
UK
"Greg Solow" <Gregmogdoc@surfnetusa.com>@autox.team.net on 24/09/99
04:44:58
Please respond to "Greg Solow" <Gregmogdoc@surfnetusa.com>
Sent by: owner-morgans@autox.team.net
To: "William G. Lamb, III" <lambroving@worldnet.att.net>, "Stein, Ross"
<Ross.Stein@kp.org>, "Lorne Goldman" <gomog@angelfire.com>
cc: "William C.W. Lamb" <chip@wmsbrg.com>, "Morgan Mailing List"
<morgans@autox.team.net>
Subject: Re: Cooling
When using a Raytec or any other infared heat measurment device, we have
found that the color and material of what you are measuring has a very
substantial effect on the readings obtained. A black metal object, like
the
top tank of the radiator will read 20 degrees hotter F than a silver or
aluminum colored metal surface like a thermostat housing even though they
are the same temperature.
Regards, Greg Solow
----- Original Message -----
From: William G. Lamb, III <lambroving@worldnet.att.net>
To: Stein, Ross <Ross.Stein@kp.org>; Lorne Goldman <gomog@angelfire.com>
Cc: William C.W. Lamb <chip@wmsbrg.com>; Morgan Mailing List
<morgans@autox.team.net>
Sent: Thursday, September 23, 1999 3:30 PM
Subject: Re: Cooling
>
> Ross, et al.
>
> To satisfy myself as to the accuracy of the VDO water temperature gauge
> in my 4.0 Plus 8, I had the water temperature measured at the top and
bottom
> of the radiator near the location of both sensors, i.e. that for the fan,
> and that
> for the gauge, with a Raytek infrared gun. The fan kicks in for a few
seconds
> whenever the gauge reads ~ 99 - 102 C. The actual water temp at the
return
> elbow is 93 C. +/- 1. At the same time, the temperature at the top of the
> radiator is ~ 88 C. So... the VDO is most likely reading 12 - 14 C higher
> than actual water temperature. I know this info will come as a relief to
many
> of you. It may also apply to owners of 3.9's since I believe the
thermostat
> housings are the same, but you will need to check the VDO part numbers
> for the 3.9 and 4.0 to see if they are the same.
>
> Regards,
>
> Willie
>
> Land Rover Specialist
> NAS 4.0 Litre Plus 8 (R-11953)
> MSCC # 9096, Morgan 3/4 Owners Group
>
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