Low Oil Pressure Question.
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Low Oil Pressure Question.
Hey guys, I have the 240ci Straight-6 in my 66 F100, and Recently I had my oil changed to Shell Rotella-T 15W40, it did have 10W30 Rotella-T in it before, but the guys that did it overfilled it by one quart, so I had it drained and replaced with the 15W-40, my Owner's manual said this would be much closer to what I should be running in it for the climate I'm in. really didn't want to leave anything to chance with this engine, I want it to stay nice. Anyway, what I noticed is now the Oil pressure is sitting around 30 psi or alittle less when the engine is running, and it used to be around 55-60 psi. Any ideas whats going on here? I'm not sure what oil was in it before I changed it for the first time, all I know is it was pitch black. I'm worried this is too low for this engine.
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Joined: Jun 2014
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From: California
Welcome to FTE.
There should be some fluctuation of pressure as the engine speed changes. Is that the oil pressure reading at idle or at speed?
The rule of thumb I heard from a local rebuilder is at least 10psi for every 1,000 rpms, so 30 psi at idle should be fine, but might be a little low if you're seeing that on the highway.
The sudden change is a little troubling but may have more to do with the gauge than something inside the engine.
~Steve
There should be some fluctuation of pressure as the engine speed changes. Is that the oil pressure reading at idle or at speed?
The rule of thumb I heard from a local rebuilder is at least 10psi for every 1,000 rpms, so 30 psi at idle should be fine, but might be a little low if you're seeing that on the highway.
The sudden change is a little troubling but may have more to do with the gauge than something inside the engine.
~Steve
Fleet Owner
Joined: Jun 1999
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From: Creedmoor, North Carolina
Your engine was designed to run straight 30w oil. Spend all the money that you want to make yourself happy on Rotella and other exotic name oils, but any 10W30 bottled recently is better than anything 50 years ago.
I think guys spend far too much time on pressure readings from old worn out equipment. If there is oil in the engine and the pressure is flexing you probably OK.
John
I think guys spend far too much time on pressure readings from old worn out equipment. If there is oil in the engine and the pressure is flexing you probably OK.
John
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
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I'm honestly not sure, it only has around 110,000 miles on it, runs whisper quiet with no valve chatter or ticking, so I'm at a loss as to why this is happening, it just seems really strange to me that it would have that much of a drop from going to what was in it to the 15W-40, even if it was Straight 30W, I wouldn't think it would make that much of a difference...
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From: Creedmoor, North Carolina
You could have been getting a false reading before, don't know. If the oil is up on the stick, the engine is humming, it's very likely OK. Get some good music playing and drive. 
John
John
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Yeah, I had another thought, if the old filter was clogged full of gunk, would it have caused a pressure reading that was much higher than what I'm getting now? And about the music - my F100 doesn't have the optional radio lol
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Joined: Jun 2014
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From: California
I'd say it's worth investigating further--even just if it's for peace of mind. I'd get a cheap mechanical gauge and set it up temporarily to confirm (or not) the pressure readings you're currently getting.
Back in the day, it was pretty uncommon to see a motor reach the 100k mark. If you're at 110,000 with no rebuild, a reading of 20-30psi might be about right. As jowilker has said, if everything else is working ok (no smoke, decent power, etc) the low pressure isn't a deal killer--just don't overwork it.
~Steve
Back in the day, it was pretty uncommon to see a motor reach the 100k mark. If you're at 110,000 with no rebuild, a reading of 20-30psi might be about right. As jowilker has said, if everything else is working ok (no smoke, decent power, etc) the low pressure isn't a deal killer--just don't overwork it.
~Steve
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Yeah, I was thinking, I wonder if the old dirty oil, coupled with a clogged filter would lead to those higher readings, then the fresh oil + filter, cleaning out the oil passages, would expose a weak oil pump.