Jim, Derf,
Just to clarify: What I did was simply to find out what water temp, in
degrees F, I was running when my temp gauge read just below N, right on N,
and just above N. I did the same thing with my MGB-GT. Since the temp
gauge reads water temp immediately prior to the water exiting the head,
going through the top hose, and dumping into the rad; I feel very
comfortable that I got a pretty good idea of what my temp gauge is really
telling me when it reads anywhere around or on the N.
Both of you raise good points, here, but, as Derf said, it did give me an
accurate reading. The temp gauge AND the thermometer don't really know or
care whether they are reading pressurized coolant, or un-pressurized.
They're just reading the temperature of the liquid they happen to be in
contact with.
BTW, I run a 7# pressure cap on my Midget. Other than the time I had a head
gasket problem, I've never experienced any over-heating problems with my
Midget. Even then, I knew as soon as the temp gauge moved beyond the right
leg of the N that I had a problem. I was able to back out of the throttle,
and cruise gently to a gas station, park in the shade, and let it cool down
(never really got hot) enough for me to ad some coolant from the gallon
container I ALWAYS carry in the boot. Drove it gently all that weekend
(Roadster Factory Summer Party '98), drove it home Sunday night (about 100
mi.), and replaced the head gasket the next evening. It's been running cool
and strong (for a stock 1275) ever since.
Bud Osbourne
-----Original Message-----
From: derf [mailto:derf247@gmail.com]
Sent: Friday, May 25, 2007 1:32 PM
To: Jim Johnson
Cc: Bud Osbourne; Phil Nase; spridgets net
Subject: Re: Overheating woes > Water Wetter
Hi,
No offense, but, it will give you an accurate temperature. What you
are looking for in that case is the relationship between what your
dash mounted gauge reads and what the thermometer reads. So, if your
gauge says somewhere between C and H and your thermometer agrees, then
you can trust your dash gauge.
When you put the cap on and the pressure rises, you can still trust
your dash gauge to be in the ballpark.
Measuring the temp in that way will not give you an accurate temp for
normal running conditions, but that isn't what he was looking to
measure.
BTW, the spridget cooling system is closed and does build up some
pressure when the temps rise. Otherwise, you would loose coolant to
operating conditions and evaporation.
Cheers,
Derf
On 5/25/07, Jim Johnson <bmwwxman@gmail.com> wrote:
> Bud.... This also won't give you an accurate temperature! Recall:
>
> PV = nRT
>
> Temperature (T) is inversely proportional to P (pressure) and V
> (volume). If you leave the radiator cap off, the system is not
> pressurized thus Temperature will be different than if the system is
> pressurized as it normally would be.
>
> Big question which I alluded to the other day when Frank had his
> problem - "Is a spridget cooling system pressurized??" If it isn't,
> you are okay, but I'm thinking it has to have at least some pressure
> in it due to expansion from heat and the fact that the system is
> closed.
>
> Cheers!!
> Jim - 68 Midget in Dodge City
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