Oil Pressure weirdness

[StangLou]

Heres the deal...

Initially when I start the car up, oil pressure rises and it settles right smack in the middle of the guage. After its warmed up and driven for say 10 minutes or so, the oil pressure will drop around half a line whenever I stop the car at a light or traffic, or whatnot. Once gas is given, it goes back up and sits where its always been. In the last month (and at the same spot on the way home) when Ive stopped at a light on a pretty steep incline, the guage has actually dimmed, oil pressure almost dropped completely, and then rose back to a bit below the mid line. Again, as soon as I leave the light it goes to where its always been.
I do have an oil pan gasket leak which will be fixed within the next month, but could the leak be that bad to throw off the pressure? Could my guage or oil pressure sending unit be going bad? There is no hint of oil in the exhaust either. Any ideas on what could be causing this?

Thanks guys

 

[ss93cobra]

Could be the sending unit. How many miles are on the engine though?

 

[Black1987Stang]

how is ur oil level? the stock gauges and sending units arent always that accurate

 

[StangLou]

The engine has 113,xxx miles on it. The oil level was a bit low, but it has a tendency to get that way with the oil pan gasket leak. It was about time for an oil change so I went ahead and did it. Ill see what happens now with it.

 

[Bolt on 5.0]

I would first check oil level, then check your oil pressure with a seperate guage to make sure you have good pressure. If the car has miles on it the pressure will likeley not be where it should. maybe try some heavier weight oil if you have alot of miles on it. Also its been a while since i had a fox mustng so im not sure where the oil pan oil pan dips in the front or rear but if i remember corectly the pan dips in the front and the oil pump wpuld be here also. If so that could be the cause of oil pressure dropping on an incline.

 

[Bolt on 5.0]

I would first check oil level, then check your oil pressure with a seperate guage to make sure you have good pressure. If the car has miles on it the pressure will likeley not be where it should. maybe try some heavier weight oil if you have alot of miles on it. Also if parked on a hill and the oil runs away from the pump that could casue low oil pressure

 

[StangLou]

Also if parked on a hill and the oil runs away from the pump that could casue low oil pressure

I didnt even think of that DOH!!! Your right, the pan dips in front which is where the pump is. Ill see if the pressure stays put with the fresh change. If so then its more than likely just getting low due to the leak. Gotta love project cars!

maybe try some heavier weight oil if you have alot of miles on it.

I run a 10W30 in it now. Could a 10W40 help some, or could that be a bit to heavy for the winter months?

 

[StangLou]

Well after a fresh oil change and driving it for a few hours today, its still doing the same thing. Initial oil pressure now is a little higher, but it still drops to the same level on the guage after 15+mins of driving. Im guessing the oil pressure regulator/sending unit, or the pump is about to go. Guess the K member will happen a bit quicker than I wanted since weve got to drop that to take off the oil pan. Any other ideas on what it could be???

 

[bobcatv8]

What you describe sounds like perfectly normal readings to me. My '88 LX has done that since it was brand new. Every engine I have ever built has done similar ups and downs too. As long as your oil level is correct I don't see any problem.
Also the sump and pick up is in the rear of the pan. The little front sump is there just for oil pump clearence. If your car is facing uphill your oil pump pick-up is fully covered in oil. If this reading is a new occurence the only thing I can think of is maybe a small crack in the oil pump pick-up tube.
BTW, I run 20w50 and have since new. 171,000 miles on it now.

 

[TrophyHead]

I agree with BobcatV8 mine does the same thing. Someday I should get an Autometer.

 

[StangLou]

Well I do feel a little better now that some other guys have the same issue and its normal. I guess I cant expect the cars functions to stay as they always have lol. The pressure is staying within an acceptable level, its just something thats started within the last couple months.

Someday I should get an Autometer.

Im very tempted now to go ahead and install some good guages. At least I would know what is actually going on instead of wondering if its just old equipment fluxuation.

I run 20w50 and have since new. 171,000 miles on it now.

No issues with it huh? How hard is it on an engine to switch oils around 100,000 miles? Ive been debating on switching to a 10w or 20w40.

 

[Zero_chance]

My oil pressure used to do that until I fixed the leak at the rear intake. Now its rock steady at whatever reading it settles on after its warmed up.

 

[DMAN302]

Stock gauge does not provide a reliable source to determine what is really going on under the hood..you need a true pressure gauge (autometer..etc) to find out the TRUE pressure under the circumstances you were discussing.

 

[stroked86]

this usually has one of two answers..... one the sending unit is bad or going bad, like others have said that and the gauges arent the best... the other is what happened with my car the gasket between my pump and the pickup split allowing oil leak before getting to the pump and it was causing the pressure to drop when the car was below 1000 rpm or so then it would go back up as rpm increased.. mainly doing it at lights. a crack in the pick-up or one of the gaskets could be the issue, the oil pan gasket itself should not effect the pressure becuase the pressure is measured after the pump in the block..

 

[StangLou]

Thanks guys, now Ive got a few things to check out once I get the pan dropped.
I may try a new Oil Pressure sending unit just to rule it out, but once I drop the pan Im pretty much replacing everything in it. That way Ill know for sure the engine will have plenty of oil once the spray goes on