Oil Pressure gauge freaking out

-
SRT_DSTRHOLC

SRT_DSTRHOLC

Well-Known Member
Joined
Mar 20, 2008
Messages
6,468
Reaction score
204
Location
USA
So I have a mechanical Autometer gauge and on start up I get 70psi on my new engine, but when it starts to warm up the gauge will flutter between 60-70 and then 40-60 when fully warm. I am trying to figure out if this gauge is crap or if I have a bigger issue. I wish I could upload a video, but IDK if it will let me up load a video as I would a picture.

Also when I mean fluttering... I mean 40-60 constantly, not slowly just back and fourth.
 
Have you bled the line to the gauge? When it is running crack the line at the gauge with a rag handy and let it bleed out any air in the line, then re tighten.
 
d55dave said:
Have you bled the line to the gauge? When it is running crack the line at the gauge with a rag handy and let it bleed out any air in the line, then re tighten.
Click to expand...

I tried to bleed it today with gauge off...that wasn't smart haha, but I will try the cracking the line. But would air in the line make a difference? It seems that air or oil pressure would just be the same no?
 
Air is compressible and the spring action of the bourdon tube in the gauge can work against it causing a bounce.



Try the simple things first......
 
d55dave said:
Air is compressible and the spring action of the bourdon tube in the gauge can work against it causing a bounce.



Try the simple things first......
Click to expand...

I appreciate it, but how can you get all the air out if the oil drains back into the engine and their is always air in the crankcase, coming from breather etc
 
The oil cannot drain back to the engine as the end of the line at the gauge is not open - like your finger over the end of a straw. Try to keep the line to the gauge as short as possible - no excessive length or loops as this too can cause a gauge fluctuation. Be sure to have enough length though to allow for engine movement. Also the plastic line is crap, try to find the brass line if you can.
 
d55dave said:
The oil cannot drain back to the engine as the end of the line at the gauge is not open - like your finger over the end of a straw. Try to keep the line to the gauge as short as possible - no excessive length or loops as this too can cause a gauge fluctuation. Be sure to have enough length though to allow for engine movement. Also the plastic line is crap, try to find the brass line if you can.
Click to expand...

Do you mean to say the end of the line at the clock is not open? But how does the oil from the engine enter the line and reach the gauge if it's not open. I am not trying to troll. I am using the Bradied line for the gauge.

Also I just read that it could be a sign of low oil in pan, I will check oil and add some more to see if it changes.
 
d55dave said:
The oil cannot drain back to the engine as the end of the line at the gauge is not open - like your finger over the end of a straw. Try to keep the line to the gauge as short as possible - no excessive length or loops as this too can cause a gauge fluctuation. Be sure to have enough length though to allow for engine movement. Also the plastic line is crap, try to find the brass line if you can.
Click to expand...


Do not use copper line. Copper work hardens with vibration and will eventually break from fatigue.

I use the nylon tube and carry a spare in the glove box.
 
Are you sure that it's not your gauge?

Do you have another gauge that you can try?

Or put that gauge on another car and see if it still fluctuates?
 
The oil line comes off the back of your engine, where the electrical sender used to be, and then goes to the gauge. Obviously it is open at the engine end (to allow oil pressure into the line), but at the gauge end the line goes into the bourdon tube in the gauge, which is sealed. The pressure of the oil expands the bourdon tube in the gauge which in turn moves the needle. As no air cannot enter the line at the gauge end, the oil cannot "drain back"into the engine, much like if you draw liquid into a straw and then put your finger over the end of the straw the liquid cannot drain back out.

The point of this all is that air which is trapped in the line to the gauge is compressible and can contribute to needle bounce.

The first step to do is bleed the line with the engine running, and tighten the fitting back up with it still running. If you still have needle bounce try a different gauge. You can also try hooking the gauge directly to the engine to see if the needle bounces there.
 
krazykuda said:
Do not use copper line. Copper work hardens with vibration and will eventually break from fatigue.

I use the nylon tube and carry a spare in the glove box.
Click to expand...

Good point about the copper, but to me it is more durable than the nylon, especially in places you cannot see like under the dash. I believe (someone please correct me if I am wrong) that nylon tube oil pressure line is not allowed at most drag strips.

Either way it sounds like he has a good quality braided line.
 
So the pressure is high when it's cold, lowers some as it warms and lowers a little more when it's warm. What's the problem?
 
RustyRatRod said:
So the pressure is high when it's cold, lowers some as it warms and lowers a little more when it's warm. What's the problem?
Click to expand...

I agree, the pressure itself is normal. The way I read his post though he was concerned about the gauge (needle) bounce, not the amount of pressure.
 
d55dave said:
Good point about the copper, but to me it is more durable than the nylon, especially in places you cannot see like under the dash. I believe (someone please correct me if I am wrong) that nylon tube oil pressure line is not allowed at most drag strips.

Either way it sounds like he has a good quality braided line.
Click to expand...


Yeah, it's the lesser of two evils here. I've also had the nylon break in my interior once about 8 miles from home.

I had to start the car , get it up to speed, and coast from light to light all the way home to keep the oil from getting all over and draining the engine. That's why I carry a spare in the glove box now.... :banghead:
 
if it fluctuates, you may be sucking air, but I doubt it. Air in the line generally dampens the needle swing. When you crack the fitting (in a rag) the needle usually tightens up and a little vibration is typical. if your really looking for the least amount of air, invert the gauge and drip oil into the sender hole until it overflows, then hook it to the line. fluttering over 20 psi is not normal. Try this, introduce a little air INTO the line and see if it dampens the needle any. Air is compressible but wont affect the reading. The good gauges have a damper in them, or so its said.
 
krazykuda said:
Are you sure that it's not your gauge?

Do you have another gauge that you can try?

Or put that gauge on another car and see if it still fluctuates?
Click to expand...

Trying this tomorrow, different gauge and this gauge on different car
 
d55dave said:
I agree, the pressure itself is normal. The way I read his post though he was concerned about the gauge (needle) bounce, not the amount of pressure.
Click to expand...

The gauge bounces rapidly from 40 to 60 faster than you can clap your hands. Like waving your finger back an fourth fast, that's how the needle moves from 40-60 psi
 
d55dave said:
The oil line comes off the back of your engine, where the electrical sender used to be, and then goes to the gauge. Obviously it is open at the engine end (to allow oil pressure into the line), but at the gauge end the line goes into the bourdon tube in the gauge, which is sealed. The pressure of the oil expands the bourdon tube in the gauge which in turn moves the needle. As no air cannot enter the line at the gauge end, the oil cannot "drain back"into the engine, much like if you draw liquid into a straw and then put your finger over the end of the straw the liquid cannot drain back out.

The point of this all is that air which is trapped in the line to the gauge is compressible and can contribute to needle bounce.

The first step to do is bleed the line with the engine running, and tighten the fitting back up with it still running. If you still have needle bounce try a different gauge. You can also try hooking the gauge directly to the engine to see if the needle bounces there.
Click to expand...


Thank you
I apreciate your help and everyones
 
With modern electronics, there's no reason whatsoever to run an oil line into the car. Jes sayin.
 
You must log in or register to reply here.
-

Back
Top