no oil pressure when engine is warm and idles down

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

too many issues

New member
Joined
Sep 8, 2011
Messages
1
Reaction score
0
Sorry, first time user. My son was deployed to Afghanistan last year and when he was gone, i purchased a 1990 xlt w/ a 351w for him. Ruff, ruff shape. The problem i am having, when it has been driven for a while, coming off the interstate the oil pressure drops out. The rpm's are still above 600, but no readings on the gauge. I had to pull over and put it in park, throttle it up to 1100 + before it came back. I have replaced the sending unit, , and the pressure has gone up on the gauge. But it only seems to do it after a hour long drive. I am running 10 W 30.. Short of pulling the engine, I am at a lose.

 

Rons beast

Active member
Joined
Dec 13, 2007
Messages
1,537
Reaction score
13
Location
Florida..in my mind , sitting on the beach
Thanks to your son for his service.

When you show no oil preasure, are there noises from the engine? Ticking, rattling?

How many miles on the engine?

If there are no noises, and you changed the sender, it probably is a gauge issue. Find a shop that can check the preasure with a mechanical gauge, at various eng. rpms. That will tell you if you really have a preasure problem or if the gauge is reading incorrectly.

Good Luck

 

miesk5

96 Bronco 5.0
Staff member
Moderator
Joined
Oct 18, 2005
Messages
9,071
Reaction score
1,018
Location
Floating in the Pacific
yo,

Test & Installation Tips in a 90;

"...My oil pressure gauge was reading on the "N" of the NORMAL range. After doing some research it seemed like it could be the oil pressure switch, also known as a sensor or sending unit.

Disconnect the wire from the switch, ground it to the truck and turn the key on. If your gauge quickly moves to the left, the problem is most likely the switch.

The switch on my 5.8 is located near the oil filter. It is in a difficult spot to work on so I advise that you go to NAPA and get an Oil Pressure Switch socket to do the job. The cost is about $7-$8, this will save you time and will help you reinstall the new switch. Wrap some teflon tape around the threads and install. Make sure that it is in tight, I don't know about torque specs, I just put mine in quite snug. Hook the wire back on and start your engine. For me it was the cure. My oil pressure now reads over near the "M" on NORMAL..." miesk5 Note; The stock gauge & Sender will drop off after pressure reaches a certain level. You might actually have 5 psi, but the gauge will read 0 PSI..."

Sender Location pic in a 90 5.8

oil-pressure-switch.jpg

Source: by SeattleFSB (Seattle FSB) at SuperMotors.net

btw,

Oil Pressure Mod to Actual PSI "...short R in PCB..." info & NAPA Sender, etc. Source: by Steve83 (Steve, That dirty old truck) at SuperMotors.net

senderoilpress.jpg

The oil pressure gauge is a magnetic gauge movement consisting of three primary coils, one of which is wound at a 90-degree angle to the other two. The oil pressure system uses a switch and a fixed resistor; the resistor is attached to the engine wiring harness. A primary magnet, to which a shaft and pointer are attached, rotates to align this primary field, resulting in pointer position. The bobbin/coil assembly is pressed into a metal housing which has two holes for dial mounting. There are no adjustment calibrations or maintenance required for this gauge.

Sender Failure; "Corrosion or faulty electrical connections; If the oil pressure gauge is pegged low after the engine is running, or is pegged high after the engine is running, or if there is intermittent illumination of an oil pressure indicator light, the sender could be faulty. Related Components to Check; All appropriate electrical connections to and from the sender The oil pressure gauge or indicator light; Appropriate fuses (see Shop or Owner’s Manual for fuse layout)..." Source: by MOTORCRAFT®

 

swampthing

New member
Joined
Feb 2, 2005
Messages
636
Reaction score
1
Location
New Jersey
not to be a worse case person but it could be the pump getting weaker...they tend to do that if its original pump ive went through many of them...you need roughly 10 psi for every 1000 rpm...also could be thin oil how old is it when was it changed..just throwin my 2 cents to help out

 

nelbur

New member
Joined
Oct 30, 2010
Messages
132
Reaction score
0
The low oil pressure at idle with hot oil is likely due to worn bearings that let the oil escape faster than it can be pumped by an idling engine. In my opinion 10W30 is just way to thin an oil for a high mileage engine. Yes I know that is what the owners manual says to use. I would change to 20W50 and see if the pressure reading will stay in the bottom of the normal range at idle when the oil is warm. If not, you might want to add some oil thickener like STP. When my original engine was on it's last legs, I was using 20W50 and two bottles of STP just to keep the pressure up to the bottom of the normal area. Ran it for years like that.

 

Bronco Kid!

New member
Joined
Aug 26, 2011
Messages
68
Reaction score
0
Location
Silverdale Washington
The low oil pressure at idle with hot oil is likely due to worn bearings that let the oil escape faster than it can be pumped by an idling engine. In my opinion 10W30 is just way to thin an oil for a high mileage engine. Yes I know that is what the owners manual says to use. I would change to 20W50 and see if the pressure reading will stay in the bottom of the normal range at idle when the oil is warm. If not, you might want to add some oil thickener like STP. When my original engine was on it's last legs, I was using 20W50 and two bottles of STP just to keep the pressure up to the bottom of the normal area. Ran it for years like that.
i agree 20w50 is the way to go!!

 

Seabronc

New member
Joined
May 22, 2004
Messages
7,315
Reaction score
35
Location
North of NYC
Just to chime in with the chorus, 20W50 has been keeping my old engine running without a hitch for several years now. I also add two bottles of Lukas stabilizer.

Good luck,

peace.gif


 

Members online

No members online now.

Latest posts

Forum statistics

Threads
22,509
Messages
135,880
Members
25,108
Latest member
Utahstroke
Top