oil pressure drops as car warms up.

jforish · Mar 21, 2006

I have a 302 that has about 100,000 miles on it. When the car is started cold the oil pressure is in the normal range. as the car heats up the oil pressure will drop to the bottom of the oil pressure gauge at idle but will increase into the normal range between 900 and 1100 rpm, the longer it is ran the higher you have to rev it to get normal oil pressure. The engine does not leek or use any oil and it still runs stong and smooth except for this problem. does anybody know what could the problem could be?

Marlboro_Man · Mar 21, 2006

I take it this is coming from your STOCK oil pressure guage?

If so you need to get an aftermarket gauge on that thing and see what it does. The stock gauges are natoriuos for being nothing more than dummy lights. Oil pressure is not something you want to play with so i would get a real gauge on there asap and see what its actually doing.

PRO50SC · Mar 21, 2006

Marlboro_Man said:
I take it this is coming from your STOCK oil pressure gauge?

If so you need to get an aftermarket gauge on that thing and see what it does. The stock gauges are notorious for being nothing more than dummy lights. Oil pressure is not something you want to play with so i would get a real gauge on there asap and see what its actually doing.

+1 for sure. You will be surprised!!!

srothfuss · Mar 22, 2006

Besides getting an aftermarket gauge for Oil PSI I'll add this: When you start your car, the oil is cold. When oil is cold it is thicker and less resistant to flow. This is why your pressure reading is so high in the mornings or at initial start up. (BTW: the oil pump has a pressure relief of ~60PSI) As the motor warms up, the oil thins out slightly and becomes easier to move throughout the motor. As the engine speeds decrease, your pump also decreases in speed and that is why you see a drop in oil pressure.

Now for the technical bit. The general rule is about 10 PSI for every 1,000RPM (across all engine makes.) Fords guidline for proper oiling is 30PSI @ 2000RPM warm idle.

jforish · Mar 22, 2006

I went out and got an autometer oil pressure guage from autozone and installed it last night. On my way to work this morning the oil pressure was at 25 psi at idle when the engine was cold. As the engine heated up it droped to zero at idle. I only live 5 miles from work, it only takes me about 10 min to get here. It idles right at 600-700 rpm. If I raise the rpm to 900-1000 oil pressure will rise to about 20 psi when the engine is hot. at 3000 rpm cold it is at 40 psi, when hot it is only at 30 psi. I normally use 10w-30 but because of the pressure drop I tried 20w-50(at my last oil change) with the same low oil pressure result. I change my own oil every 3000miles. I use quality Valvaline oil and fram oil filters only. Any other suggestions to my problem would be very helpfull.

Daggar · Mar 22, 2006

Help my recollection guys:

Arent' the Fram filters the ones with the cardboard filter elements (I just don't remember)?
If so, swap to a different brand of filter and see what your pressure does.

If youdon't have it in your budget to do a rebuild right now and want the car to run for while longer but also don't have any other issues... it may a great time to toss a high volume oil pump in to keep slippery stuff in the critical areas. IMO, this is what high volume oil pumps are for!

srothfuss · Mar 22, 2006

Yeah, Fram filters are no good. Use a Motorcraft filter (same price as fram or cheaper) but without the cardboard construction.

Modular2v · Mar 22, 2006

it is normal for it to drop some...as the oil warms up it becomes thinner

Modular2v · Mar 22, 2006

Daggar said:
Help my recollection guys:

Arent' the Fram filters the ones with the cardboard filter elements (I just don't remember)?
If so, swap to a different brand of filter and see what your pressure does.

If youdon't have it in your budget to do a rebuild right now and want the car to run for while longer but also don't have any other issues... it may a great time to toss a high volume oil pump in to keep slippery stuff in the critical areas. IMO, this is what high volume oil pumps are for!

WOW couldnt agree more

anotherstangfan · Mar 22, 2006

Hello, Jforish

My 1989 5.0 started doing the same thing around 100,000 miles. I ignored it for about 6 months thinking it was just the gauge because I did not notice any problems. Then my engine started knocking after it warmed up, I recommend adding 1 bottle of Lucas Oil Stablizer next time you get an oil change, it will thicken up the oil and probably restore your oil pressure. Best to do this before anything gets any worse.

Modular2v · Mar 22, 2006

anotherstangfan said:
Hello, Jforish

My 1989 5.0 started doing the same thing around 100,000 miles. I ignored it for about 6 months thinking it was just the gauge because I did not notice any problems. Then my engine started knocking after it warmed up, I recommend adding 1 bottle of Lucas Oil Stablizer next time you get an oil change, it will thicken up the oil and probably restore your oil pressure. Best to do this before anything gets any worse.

that would be a sad, sorry excuse for even a band aid.... 1st get a real guage wired up to it and make sure it is not the horrible stock dummy guage. If the problem persists after that you might want to be looking into a new oil pump or maybe.....worse

jaymac · Mar 22, 2006

jforish said:
oil pressure was at 25 psi at idle when the engine was cold. As the engine heated up it droped to zero at idle. If I raise the rpm to 900-1000 oil pressure will rise to about 20 psi when the engine is hot. at 3000 rpm cold it is at 40 psi, when hot it is only at 30 psi.

From my understanding, those #'s are not good at all. I just put an autometer in my car last week as my stock gauge #'s scared me.
The min. acceptable # as I understand it is 20+ @ hot idle. It should be around 50 @ cold idle. Then normal driving should be 45-60.
I would double check and make sure all your grounds for the gauge are good and that your other connections are also good. Did you use the sending unit that came w/ the Autometer??

sgarlic · Mar 22, 2006

I wouldn't bother adding that Lucas stuff. If you read over at the Bobistheoilguy forums at all, there's a real interesting thread with pictures, etc, where the guys showed how adding this caused the oil to foam quite a bit.

anotherstangfan · Mar 22, 2006

Theres is only a couple reasons I suggested the Lucas Oil Stablizer. The first reason is I had a new oil pump put in and it didn't do anything to restore the oil pressure. Secondly is the Lucas Oil Stablizer is only 7 dollars a bottle and it restored my oil pressure made the knock quiet down a bit. I am selling my car to a friend for parts and purchasing another stang, I am speaking from my own experience, not from what others have said.

bsedwebt70-5.0 · Mar 22, 2006

My 1993 GT did the same with 112k miles - good pressure when first started then dropped to nothing on stock guage at hot idle - checked with a real guage - it was showing 8lbs at 750 hot idle and about 50lbs cold idle - took the motor apart - needed a NEW crank - the old one was too far gone - did whole rebuild - bearings were ALL shot - good luck

DeadLifter · Mar 24, 2006

Yea if it ends up not being the gauge it's more than likely the main bearings.

Road_Runna · Jan 31, 2021

jaymac said:
From my understanding, those #'s are not good at all. I just put an autometer in my car last week as my stock gauge #'s scared me.
The min. acceptable # as I understand it is 20+ @ hot idle. It should be around 50 @ cold idle. Then normal driving should be 45-60.
I would double check and make sure all your grounds for the gauge are good and that your other connections are also good. Did you use the sending unit that came w/ the Autometer??

I just installed a glowshift oil pressure gauge on mine. Exactly as you stated above. 50 psi at cold idle. 20 psi at engine warm (6 minutes).

Adieu · Jan 31, 2021

oil pressure drops as car warms up.

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