Oil pressure gauge problem.

[kgcobra320]

About 3 months ago I installed an Autometer mechanical oil pressure gauge.
The feed line comes from the extra port near the factory oil switch and the
gauge is mounted on the A-pillar. Everything was working fine, then one day
while cruising down the highway, I notice that the gauge was reading about
10psi lower than normal. I tap the gauge and it jumps up to about where it
should, I toss it off as just a little sticky. Problem is, that it's still doing it and
tapping the guage now, does nothing. At idle the reading is right on and
when cold it does read above the cruise pressure. I also have an Accusump
with a pressure gauge on the air side. The two gauges used to follow each
other closely but now the oil one lags behind. Is it possible that the gauge
is only sticky within a certain range, 60-70psi??? Or is there something else
going on??? Is it possible that my Canton Mecca
filter is getting clogged at only 6800mi??

KG

 

[TallPaul]

Sounds like you should talk to an Autometer customer service tech as maybe the gauge is defective. As for your other speculations, I really would not know. Some have said air in the line can cause problems, but I was told by a gauge company that air in the line does not matter and all both my mechanical gauges (Autogauge by Autometer) work fine that way.

 

[kgcobra320]

Yeah, I emailed Autometer and they gave me the standard, "We don't know, but if you send it to us with the receipt we'll look at it". I had asked them about the air in the line when I first installed them and they said it was fine.

You would think if my fullflow was getting clogged that it would have been more gradual.

KG

 

[TallPaul]

Sometimes better to talk directly with the tech.

Could replace the filter and see if it changes, but a messy job.

Gary Allen may have some insite as he has studied pressure and filters a lot.

 

[kgcobra320]

I have the canister type so changing it is easy but the elements are expensive. I suppose that I could just put the old one back in if it wasn't the problem.

I was hoping that Gary would be around to provide some input as well.

KG

 

[TallPaul]

So I am wondering if you are still having the problem or if maybe it has resolved itself with a bit of driving? Maybe a fleck of crud blocking the relief valve partway open and if fell dislodged after a while.

 

[kgcobra320]

The idle pressure started showing low as well, so I changed
the filter. The idle pressure now shows normal but the
cruise pressure is still about 10psi low. I'm fairly
confident that the pressure is normal because the gauge on
the air side of the system does not reflect this problem.
Just seems like a weird failure mode for a pressure gauge.
I can see sticky or having a permenant offset but this is
just strange

KG

 

[kgcobra320]

Problem solved!

Anyone trying to decide between mech and elect oil pressure gauges might
want to consider this:

I have 2 mech oil pressure gauges in my 99 cobra. One is plumbed into the
extra block port and the other is connected to the air side of my Accusump.
After the install I noticed that during cold operation the pressures push the
100psi mark and beyond. I was a little concerned but everthing seemed to
be functioning perfectly, for about 3 months that is: Then sometime during
September I noticed that the pressures wern't normal. Low at cruise, ok at
idle, the 2 gauges not correlating anymore????

What happened????.........The cool September mornings here in New
England is what happened. It took a while for me to figure it out but that's
what happened. The pressures were already pushing the limits of the
gauges and when the temps dropped, the pressures increased. Both gauges
are now internally damaged and now have a permenant offset of about
10psi!!!!!

They were expensive and difficult to install and now they're ________!!!
I could send them back to Autometer and they would probably fix one of them
but it will be obvious to them that the limits have been exceeded and would
probably not fix both.

Most mech oil pressure gauges have a limit of 100psi and will not work at mod
motor pressures, especially during cool weather.(Maybe ok if you live in a
warm climate zone?). I did see that Autometer does make one oil pressure
gauge that goes to 150psi in the Phantom series and should work just fine.
Unfortuneately at this point I already have a bunch of the Lunar series.

Also I believe that the elect. gauges will not be damaged during pegged
operation and would probably be a better overall choice. The elect oil
pressure sending units are prone to failure though, due the vibration when
mounted on the block and would require remote mounting.

KG

 

[TallPaul]

I once had the bright idea of testing a mech oil pressure gauge with my electric air pump. Good thing the gauge only cost me $5. I flipped on the air pump while hooked to the gauge and pegged the needle. Turned off the air and the needle was somewhere midway. I manually twisted the needle back to zero and it seems fine now, but I don't want to use it anymore. I have better gauges anyway.