Oil pressure Gage showing zero

[WA_IrishPilot]

Started my truck this morning (temps around -30*F) and had just above zero oil pressure, but not in the normal range.

The truck is a 1999 Ranger with the 4.0L V6 engine. Yesterday it ran fine and didn't notice any change in pressure. There is plenty of oil in the system as I changed it in September.

I have seen references to the oil pressure switch, which I can change. But after that I am confused as to what could be causing it. I ran it for awhile with the hood open and it warmed up fine, but zero pressure.

Thanks.

 

[Haywire6000]

well if it ran for more than 5 minutes with slinging a rod you have oil pressure. So more than likely the oil pressure switch died(Mine dies about a week ago on the 2.3l was doing the same thing). You thing you can do to check is unhook the connector going to the sending unit and ground it. The oil pressure gauge should read about midway on the gauge. If it does then the sending unit is bad.

 

[70roadrunner]

if it truly had no oil pressure, you would know immediately, as it would tick loudly, then start knocking. as long as it doesn't start knocking, there should be very little damage.
it is most likely the pressure switch or a wiring issue

 

[ab_slack]

Makes one cringe running with oil pressure not showing.

The concern is if it is a sensing issue or if oil pressure is lost (i.e. oil pump failed). Only way to really be certain is to put a real pressure guage on it.

I assume you checked oil today and it is okay...September seems a long time ago if there is a leak.

A couple years ago on a 99 ranger with a 3.0L lost oil pressure completely sometime while I was driving. I was going uphill at the time, noticed something odd feeling with the engine, looked down saw the gauge at zero, pulled over stopped the engine. Oil level was fine. Engine was seized.

Last year, the same 99 ranger, when starting the engine showed zero oil pressure and it would come up a few seconds later typically but sometimes it wouldn't. Given the history that was concerning so we plumbed an actual gauge in parallel with the switch using a T fitting.

The dash gauge on the 99 is a fake gauge that is run from a switch so always shows in the middle. I believe the switch threshold is like 5 psi but I may be wrong. If you are below 5 psi that is probably not good.

 

[ab_slack]

if it truly had no oil pressure, you would know immediately, as it would tick loudly, then start knocking. as long as it doesn't start knocking, there should be very little damage.
it is most likely the pressure switch or a wiring issue

Good point. I think the 4L is more like the 2.9L. I know the 2.9L make all sorts of valve train noise when not getting oil. The damn 3.0L didn't make any noise at all to suggest a problem till it was too late.

 

[bigmark303]

The minute the oil pressure gauge does not function or read very low the engine should be turned off without hesitation.

By no means until you have determined that you have enough oil in the engine and the oil pump has not failed should the engine be started and running except to check oil pressure with a manual gauge. One quick and easy way to destroy an engine is no lubrication.

Start with checking the oil level. Make sure its full on the dipstick. If that checks out then move to the oil pressure sending unit on the engine. Make sure its plugged in securely and all wires are in good order. If that looks normal get a hold of a manual oil pressure gauge. Use this to verify if you even have oil pressure when running and what pressure it is. If you come back with nothing then the oil pump is bad. If you have pressure and it is adequate (15-30psi at idle) for the engine the sending unit is bad.

 

[WA_IrishPilot]

if it truly had no oil pressure, you would know immediately, as it would tick loudly, then start knocking. as long as it doesn't start knocking, there should be very little damage.
it is most likely the pressure switch or a wiring issue

It does tick or knock, but that goes away after a minute once the engine warms up. It was something like -50 or so after windchill last night. Once it has been running and warm everything sounds normal.

I am frustrated as it ran fine yesterday, then this morning zero. My uncle was a mechanic for Mazda and thinks it is the oil pressure switch as if I truly had zero oil (which I have near the full mark on the dipstick) there would have been other indications in the past few days.

Since there is plenty of snow under my truck, I have yet to see a oil leak. And to go through 5 qts between September and now is impossible as I check it once a month.

(Edit #1) I rechecked something. When I put the key in and turn to ACC the oil pressure gauge DOES move and comes up a bit, but the bit is 1/2 between pure zero and the red-line

 

[Kowboy]

I also have had the oil pressure switch to go bad in my 2000 3.0. It scared me to be driving down the road at 40 mph and not see the gauge needle move at all. The first good bump in the road and it started to show normal pressure. I also assume that you are running the correct viscosity. -30 almost sound like a misprint to me. I hope you're staying warm. We have 20 degrees here and my little Ranger will not put out any heat for the first 5-6 miles of driving.

 

[ab_slack]

It was something like -50 or so after windchill last night. Once it has been running and warm everything sounds normal.

Wind chill is a dynamic function relating to heat loss providing a comparison of rate of heat loss compared to there being no wind. So if it is -5 deg but the wind chill is -50 as an example, it "feels like" it is -50 cause you lose heat much faster with the wind than if it were -5 deg and no wind. Your truck however, will cool quicker as well when turned off but once it gets to -5 deg it won't go less. It never gets down to -50.

I also have had the oil pressure switch to go bad in my 2000 3.0. It scared me to be driving down the road at 40 mph and not see the gauge needle move at all. The first good bump in the road and it started to show normal pressure. I also assume that you are running the correct viscosity. -30 almost sound like a misprint to me. I hope you're staying warm. We have 20 degrees here and my little Ranger will not put out any heat for the first 5-6 miles of driving.

When we re-plumbed our 99 ranger to put a real gauge in parallel with the dash gauge because of the way it wasn't coming up so we could see the pressure, the problem with the dash gauge stopped.

I wonder if the problem was the ground connection of the stock gauge into the block such that when it was cold it didn't connect. We didn't replace the switch at the time.

 

[WA_IrishPilot]

I also have had the oil pressure switch to go bad in my 2000 3.0. It scared me to be driving down the road at 40 mph and not see the gauge needle move at all. The first good bump in the road and it started to show normal pressure. I also assume that you are running the correct viscosity. -30 almost sound like a misprint to me. I hope you're staying warm. We have 20 degrees here and my little Ranger will not put out any heat for the first 5-6 miles of driving.

Nope, -30 or so is true. Being in North Dakota we have gotten hit with some pretty cold weather. Besides being flat it doesn't help.

 

[WA_IrishPilot]

Wind chill is a dynamic function relating to heat loss providing a comparison of rate of heat loss compared to there being no wind. So if it is -5 deg but the wind chill is -50 as an example, it "feels like" it is -50 cause you lose heat much faster with the wind than if it were -5 deg and no wind. Your truck however, will cool quicker as well when turned off but once it gets to -5 deg it won't go less. It never gets down to -50.



When we re-plumbed our 99 ranger to put a real gauge in parallel with the dash gauge because of the way it wasn't coming up so we could see the pressure, the problem with the dash gauge stopped.

I wonder if the problem was the ground connection of the stock gauge into the block such that when it was cold it didn't connect. We didn't replace the switch at the time.

I'm not able to do what you said of putting a real gauge in parallel. I just need to get the truck working. ESP since this happen just over night. Everything was fine yesterday, then I wake up and bam nothing. There is some fluctuation in the gauge, but nothing to bring it into the normal range.

 

[Earl43P]

If the pressure were truly zero, you'd hear valvetrain clatter first as in immediately after starting it up, then serious knocking deep down (crank bearings), then it'd seize in just a few minutes of running.

The senders are a switch, as said. Sounds like yours went bad. Cheap part, PITA to get to.

I'd drive it if it sounds normal.

 

[WA_IrishPilot]

If the pressure were truly zero, you'd hear valvetrain clatter first as in immediately after starting it up, then serious knocking deep down (crank bearings), then it'd seize in just a few minutes of running.

The senders are a switch, as said. Sounds like yours went bad. Cheap part, PITA to get to.

I'd drive it if it sounds normal.

It sounds bad once you start it, but the oil pressure gauge does come up. Just not ALL the way up. I have a friend coming to take me so I can get the part. I believe it's the sender that's like 14 buck part. Pain to get to, but will be done.

 

[WA_IrishPilot]

So, I changed the oil pressure switch and still the same amount of pressure. 1/2 way between pure zero and redline. I added some oil, and the truck starts, stays on and gets warm, but doesn't peak heat wise.

I wouldn't know the sound of knocking or anything (which sucks). Don't have the ability to change the oil pump pickup screen so I am sorta suck. Still have no clue why one day it was all fine and dandy, then the next nothing.

 

[Spott]

Check your wiring by grounding the sensor wire. If the wires are good, the gauge will read normal. If that doesn't help you find the problem, get a mechanical pressure gauge and see if your oil pressure isn't truly low.

Spott