Mechanical, under the hood......and I think they say that marshalls are made in the usa??
Here is what the marshall person replied to my email:
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It is hard to know if you purchased a new gauge or not. Assuming the
vendor was honest and the gauge was new you most likely are seeing some zero
offset due to pressure build up in the case which is typically only
noticed on a low pressure gauge (i.e. 0-15 psi or less). Did you buy a 0-15 psi
range? ALL liquid filled gauges are sealed so if the gauge gets hot pressure
builds up inside the case and offsets the actual pressure inside the movement.
This is typically only a problem if the gauge is getting really hot and
the pressures you are trying to measure is low (i.e. less than 5psi).
To ensure accurate pressure measurement if the gauge is hot, vent the case
before taking your reading by gently pulling up on the fill plug facing up
to equalize the pressure inside the case with the atmosphere, then
carefully reseat the vent plug making sure it is secure so no liquid comes out.
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My reply back:
Thanks for the reply
I do believe it is brand new and yes it is a 0-15 lb unit (engine turned
type).
It looked like it had never been installed and like I said it was one of
several he had, which he said were new. The fitting was perfect and
clean, no fuel smell or anything.
That said, one thing I noticed is that as the car cooled off the gauge
would read some pressure when restarted....2.5 lbs. And go down as the
engine heats up.
I immediately removed the gauge and put my old one (an old mr gasket,
non filled type, the lens is bad) on and it reads 5.5 lbs as it has
always read and where i had set the regulator.
The problem with venting the gauge as you suggest is that on my gauge
(the marshall one) the fill plug is at the 5 o'clock position, facing
down when installed. So I would have to install it upside down in order
to pop the plug out to vent as you suggest while it is still on the vehicle.
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His reply back to me:
The Mr Gasket dry gauge (we make those also) does not have the issue because
the case is not hermetically sealed so pressure build up is not a problem.
Vent and seal the gauge when it is hot so you have the base pressure in the
case at the "normal operating temp". This may help your readings. If this
does not help your best options are to:
1. use a dry gauge, or
2. use the ET gauge remote mounted for easy venting when necessary.
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My last reply:
I guess I have a really hard time understanding this.
Please don't take this the wrong way but, where were these gauges intended to be used?
I have seen many of these liquid filled gauges being used on cars at shows etc, many with much larger and hotter running engines than mine and never heard that they are just for show, which it seems like in effect you are saying.
I ram my car for only about 15 minutes and it was hot enough under my hood to make a gauge that starts off reading 4 lbs end up reading zero and you seem to be saying that is the design. How is that possible?
And to fix that I have to vent pressure in the case, after somehow mounting it so it will b upside down and in a vertical orientation so I can "vent the case" without any goo coming out while at normal operating temps ....and then it sounds like I then have to settle for incorrect pressure when cold?
One other issue is, "normal operating temperature" will vary whether its a cold day or hot day, etc, and temps will go up and down depending on how hard the engine was run etc.....how can anyone use this gauge to get readings that can be relied on? Am I supposed to vent this thing and then run the engine to "normal operating temp" given whatever conditions everytime I want to be able to read it accurately? And if I am forever messing with it, how will I ever know if it is giving me an accurate reading?
That doesn't make a lot of sense to me.
My oil pressure, gas level, voltmeter, vacuum and speedometer gauges (some OEM, some various brands and ages) all work accurately whether hot, cold or whatever. with only minor if any differences between differing conditions.
How can a fuel line pressure gauge being so adversely affected by normal underhood temps ne looked at as normal?
Did I buy a $40 paperweight that is designed just for looks?
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We'll see what they say back...my guess is I bought a $40 paperweight.
I am just stymied......the liquid filled gauges are not, then appropriate for under hood use? Because I would gather that ANY engine gets hot and would cause this very same issue......so the gauge is either going to be accurate when cold or when hot and inaccurate (WRONG) any other time? So how the hell will one know when a change in the reading is due to the engine being outside the "normal" temp or when there is actually a fuel delivery problem?!?!?
