Oil pressure gauge fluctuation - Yes, another one


extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
Doing a steady 80 on the interstate yesterday, all of the sudden notice the oil pressure gauge bouncing around, mostly to the low side, down to about 35, sometimes a little above, to 55-60. Pretty scary! Never went below 25, but this being my first experience with it I didn't know where it was all headed. I can be driving at a very steady 80 and it might be at a solid straight up 50 for a number of minutes, then all of the sudden start jumping around again. Letting off the gas often caused the gauge to drop 5-10 psi. At a stop light it usually drops to 25 and kinda stays there until take off again..

My view of the gauge is almost entirely blocked by the steering wheel so it's possible it's been doing this before, not sure.

Does this sound like the sending unit?

Starting to think I prefer vehicles not bother me with an oil pressure gauge :)
 

PeteK

GT Owner
Mark II Lifetime
Apr 18, 2014
2,285
Kalama, Free part of WA State
The original gauges have a known high failure rate. You can buy a new one from Autometer, specifically for the GT, that looks exactly the same, but has updated innards. About $250.
 
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2112

Blue/white 06'
Mark II Lifetime
When I replaced my smalls (all 5) I moved the oil pressure gauge further to the right where I could see it more readily.
 
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fjpikul

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Jan 4, 2006
11,495
Belleville, IL
There are plenty of posts describing this. Do a search.
 

Fast Freddy

GPS'D 225 MPH
Mark II Lifetime
Aug 5, 2005
2,685
Avondale, Arizona
Could a stretched oil pump belt be the cause of this? When was the last time you changed it and how many miles do you have on it? If not i would replace the oil pump itself then...
 
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nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,193
100% NOT an oil pump belt. Either a bad sending unit or a bad gauge. You can tell the difference by watching the gauge behavior closely. A bad gauge is typically "sticky" it will have a difficult time to move up, for example, and it may stick and then jump to the correct position. A bad sending unit, on the other hand, will cause the gauge needle to be more erratic - flicking both forward AND backward. From your brief description, it almost sounds more like a sending unit. I'd start there anyway, because they are both simple and inexpensive to replace. Let us know what happens!
 

GT@50

GT Owner
Mark II Lifetime
Dec 14, 2019
862
Issaquah
I've been waiting for a sender from Ford for a few weeks now. Ford said there's a supplier? issue. Updated today, "still waiting".
 

rnkma4

GT Owner
Jun 9, 2014
71
Santa Clarita
I had the same issue, nota4re changed my sending unit, no issues since then.
 

extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
Could a stretched oil pump belt be the cause of this? When was the last time you changed it and how many miles do you have on it? If not i would replace the oil pump itself then...
Replaced by Rich Brooks August 2021.
 
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extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
100% NOT an oil pump belt. Either a bad sending unit or a bad gauge. You can tell the difference by watching the gauge behavior closely. A bad gauge is typically "sticky" it will have a difficult time to move up, for example, and it may stick and then jump to the correct position. A bad sending unit, on the other hand, will cause the gauge needle to be more erratic - flicking both forward AND backward. From your brief description, it almost sounds more like a sending unit. I'd start there anyway, because they are both simple and inexpensive to replace. Let us know what happens!
Thank you, will def report the results.
 

extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
I had the same issue, nota4re changed my sending unit, no issues since then.
Good news, thank you (y)
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,193
I've been waiting for a sender from Ford for a few weeks now. Ford said there's a supplier? issue. Updated today, "still waiting".
Go order equivalent from Rockauto.com In stock.
 

Fast Freddy

GPS'D 225 MPH
Mark II Lifetime
Aug 5, 2005
2,685
Avondale, Arizona
37.5 psi at idle here and 75 psi at full throttle. Sometimes mine will fluctuate between 50 psi and 75 psi while cruising at part throttle. I have never felt the need to replace it. But if it were to read below 35 psi I would change the sender.
 
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extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
35 psi at idle here and 75 psi at full throttle. Sometimes mine will fluctuate between 50 psi and 75 psi while cruising at part throttle. I have never felt the need to replace it. But if it were to read below 35 psi I would change the sender.
I dunno if it should be, but when you've never seen the gauge fluctuate 25 is unnerving! 😲
 

analogdesigner

GT Owner
Mark IV Lifetime
Nov 15, 2005
949
San Clemente, CA USA
extrap, this looks like a bad sender as those are the same symptoms that I had. I am on my second replacement. I may have a new sender as I wanted a backup. Here is a graph that I did showing oil pressure versus RPM. This was done at operating temperature with the factory recommended oil.

Jay
 

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extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
extrap, this looks like a bad sender as those are the same symptoms that I had. I am on my second replacement. I may have a new sender as I wanted a backup. Here is a graph that I did showing oil pressure versus RPM. This was done at operating temperature with the factory recommended oil.

Jay
Jay - Thank you. I suspect a chart of mine would look similar: Gauge sits low ~25-30 at idle then increases with RPM. At a steady speed it can sit at 50 for a while and then just haphazardly bounce around, usually lower, sometimes a little high.

Also, the gauge doesn't appear to move sluggishly, if that's any indication. It seems to move smoothly but freely ... these are observations from an owner with no prior gauge issue experience.
 
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Nafod

GT Owner
Mark IV Lifetime
Years ago, an owner had the oil pump drive pulley fail, not the belt. Don't remember the exact cause, but when he pulled the cover, the the internal part of the pulley had failed. The pulsating oil pressure was the pump barely turning. The 5-50w synthetic oil save the engine. Kind of burnt/ black when he drained it.
Most probably the cause mentioned above, but I'd check the belt and pulley. my .02.
 
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2112

Blue/white 06'
Mark II Lifetime
I remember that. It was a failure at the pulley/pump shaft interface.

Something like a bolt that was not shimmed correctly allowed the pulley to loosen and strip out the inside diameter.
 
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nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,193
THE SKY IS FALLING!!!
 

extrap

GT Owner
Mark II Lifetime
Jul 16, 2020
1,759
Gainesville FL
THE SKY IS FALLING!!!
Kinda was for me as my oil pressure seemed to be crashing at 80 mph on the busy interstate. Not so much now, but what's the harm in discussing it? ... especially when nobody knows for sure the solution until it's actually solved.
 
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