Oil Gauge Reading LOW

[Dreadflux]

Hi everyone,

I just bought an absolutely beautiful 1991 F350 Supercab dually, manual, 7.3L IDI with the Banks turbo, only 49,000 original KMS!! I've put about 3000 kms on it, and just today, the oil pressure gauge went all the way to LOW even past LOW. When I'm idling its sitting around the L, but otherwise while driving it is showing zero oil pressure. I know this is not the case, because everything is working fine, but my engine light is also going off intermittently, and it seems when it goes past the LOW mark, the engine light comes on, then when my gauge goes back up to the L, it goes off. I've read that I need to get the actual oil pressure taken mechanically. But anyone ever see this issue combined with the engine light? Coincidence? Will the zero oil pressure produce an engine light? Thank you all for your help.

 

[franklin2]

Your truck should have the original "fake" gauge from Ford. You do not have a oil sender you have a oil switch mounted rear of the engine near the top of the bellhousing.

Ford stopped using a sender, and instead started using a switch, the same as on an idiot light type dash. Below 5 lbs it turns the light on. Anything above 5 lbs turns the light off. They installed a resistor that makes the gauge read center of the scale. Anything above 5 lbs pressure makes the gauge read in the center. Anything below 5 lbs makes the gauge read zero. You really need a set of aftermarket gauges on your truck.

 

[Dreadflux]

Thank you for the reply and the information. So this is what’s happening, see link below. I need to get it to a mechanic, should I get it towed to be safe?

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[IDIBRONCO]

There's no need for that. You know that you have oil pressure despite what the gauge says. If you didn't, the engine would be knocking in short order. The way these engines are built, as long as you have enough oil in the engine, it's almost impossible to not have oil pressure when the engine's running.

 

[Cubey]

My 87 F250's factory gauge waves around low at idle when fully warmed up, making the engine light flicker as the gauge goes up and down around the low line. That scared the last owner so he put in a mechanical oil pressure gauge to check it, and the pressure is fine according to that. So, I just ignore the flickering engine light at idle.

 

[franklin2]

Thank you for the reply and the information. So this is what’s happening, see link below. I need to get it to a mechanic, should I get it towed to be safe?

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This is what you need.

You must be registered for see images attach

 

[Dreadflux]

This is what you need.


I want! Do you have a link? Thanks for all the reply’s. I’ve found a guy here in Manitoba that knows lots about these trucks. Looking forward to getting this baby all done up.

You must be registered for see images attach

 

[nostrokes]

This is how mine acts. It's hard to see but at idle and hot it's at 20psi..

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[Jim993]

I don't know about a '91, but the Banks conversion for my '85 relocated the oil pressure sender unit to the top of the turbo. That introduces even more error to the OEM oil pressure sender because the new location is measuring oil pressure at the turbo but there is line loss caused by oil flowing through the turbo. Pressure readings there will be lower than main oil gallery pressure. In addition, the OEM Ford sender unit is not very accurate and wanders even when at its best.

I found an unused 1/8" pipe plug in the main oil gallery down on the driver/ left side of my 6.9 and plumbed a 1/8" copper tube up to the firewall above the turbo and mounted the oil pressure sender plus a mechanical gauge there. Now I know my 6.9 has 20 psi hot idle, 55 psi at 2,500 RPM.

 

[Dreadflux]

I don't know about a '91, but the Banks conversion for my '85 relocated the oil pressure sender unit to the top of the turbo. That introduces even more error to the OEM oil pressure sender because the new location is measuring oil pressure at the turbo but there is line loss caused by oil flowing through the turbo. Pressure readings there will be lower than main oil gallery pressure. In addition, the OEM Ford sender unit is not very accurate and wanders even when at its best.

I found an unused 1/8" pipe plug in the main oil gallery down on the driver/ left side of my 6.9 and plumbed a 1/8" copper tube up to the firewall above the turbo and mounted the oil pressure sender plus a mechanical gauge there. Now I know my 6.9 has 20 psi hot idle, 55 psi at 2,500 RPM.

Thanks for the message. My truck also has the banks conversion.

 

[aggiediesel01]

Another common issue is just that the connection has high resistance. Try wiggling that connector and maybe squeeze it a slight bit to make is tight if it not snug already. If that doesn’t help, these trucks have a big round bulkhead connector on the driver side firewall. All the signals pass through here. You can disconnect and reconnect this several times to clean those contacts and then again at the back of the instrument cluster there are two plugs that carry these signals. They can also be unplugged and reconnected to help clean those contacts. I’d rather fix the actual issue than have to know it’s ok to ignore a warning light.

There's another connector that signal passes through I forgot about on the passenger fender liner. That's the main engine harness connector and it gets dirty too. Unplug and reconnect it several times as well and make sure the heavy yellow wires that are at one edge of the plug haven't over heated and melted anything. It's important to clean and protect these connections from corrosion with some dielectric grease as they carry all the current to your glow plugs system and need as little resistance as possible. In fact it's better to take this load off this connector by running a separate dedicated heavy gauge cable to the GP solenoid routed directly from the starter solenoid where the main 12V distribution starts. Ford made this change in '92 and it's for a good reason but I don't think it's a high priority until it starts getting cold this fall.

 

[Donnergaard]

All good info here by previous posts. As you probably already know, the oil pressure switch/sender is located at the end of the line after all other requirements have been filled. I had similar worries with the stock gauge so I put a tee in the line below the switch and added a sender for an Autometer oil pressure gauge. My 7.3 idi holds about 7 or 8 psi at hot idle of about 750-800 rpm. It was lower but I bumped the idle up 50 rpm or so. I run 2 qts of Lucas oil stabilizer in each oil change. I’ve changed the oil every 2500-3000 miles since new in 91. I got a little concerned when after I’d been on the ranch in dustier conditions for a few years, I noticed hot idle oil pressure and running oil pressure start to drop off. Running oil pressure is running around 36 psi when warmed. I think my biggest mistake was installing a K&N air filter early in the trucks life. While they may flow slightly more air at high volume, they come in at the bottom of the list when it comes to removing dirt according to actual lab tests. I now run Wix filters on everything. I cut new oil filters open with a cutter to compare filter media and came to the same conclusion about Wix. I know I’m getting plenty of oil volume as my oil pressure gauge acts a lot like a tach when I rev the engine. I’ve had the truck since new in September 91 and it has almost 200,000 miles on it. Hope this info helps your thought process.