Low oil pressure at high RPM?

Had a scare some time into a 4 hour highway drive this past weekend, unloaded. At sustained higher RPM, say nearing 3000 my oil pressure gauge would drop. Factory gauge so gives indication of relative pressure but no numbers. Normally around O at idle and lower RPM, moderate to higher RPM in the MA range. Around 3000 RPM after 30 seconds to a minute it would go down to about O. I slowed down to keep RPM around 2700-2800 where pressure remained around MA as it normally is. After an hour or two it dropped again unless I stayed below 2400 or so. Slowed it down to 2000 RPM the rest of the way home where pressure remained where it usually is. Once off the highway oil pressure seems slightly now around N, ran normal and no abnormal noise.

Voltage remained a about 14v or a hair over. I've seen when alternator fails or voltage otherwise low the fuel gauge reads higher and all others read low... That was not happening, fuel level and coolant temp remained where they should be and no reason to doubt accuracy. Have run it at 3000-3500 sustained a time or two. Normally cruising around 3000 is no prob, and I've never sweated it as folks here say these engines were made to run on the governor all day.

Oil and filter had 6000-7000 miles on them due to my being busy, injured, and lazy. Changed oil the next day, was about 2 quarts short which it has been from time to time (leaks) with no abnormal pressure readings. I use Rotella T6 synthetic 5w40 and FL-1995 filters. Hot idle pressure was normal, normal pressure driving around that day but no sustained 3000 RPM. I know I need a real gauge, about to order one. Truck is currently out of commission probably through the weekend for unrelated reasons so cannot check for a few days at least.

Any thoughts on the oil pressure dropping at sustained higher RPM? Anyone seen a factory sender fail like this? Anyone seen low oil pressure at high RPM with these engines verified with an actual gauge?

Fqatory glorified idiot lite eh...

Get a real gauge then report findings

Mine doesn't even register anymore. If you have a bricknose you will get a warning light on the dash if you actually loose (at least less than 8psi) of oil pressure.

What year truck?

On our truck (late bricknose with the 6.9 sender and modified cluster to work with it) we recently watched the factory gauge drop lower and lower till it stopped registering at all. The mechanical gauge that's hooked up to the exact same location was reading excellent pressure. Wiggle the wire on the sender, wouldn't you know, factory gauge is back online and reading properly. So check your wiring connection to the sender, may be something as simple as corrosion building up there.

Also, yes, do get a second oil pressure gauge. Engine coolant temp gauge as well, heck even oil temp gauge if you can swing it.

I agree with above, if you are concerned about the oil pressure, get a real pressure gauge on it...

That being said, on a long haul, with high RPM's like that, the oil will thin out as it gains heat. Which at 3000 RPM, you would be putting a lot of heat in the heads, which may increase coolant temps, but you will also be putting more heat into the pistons, which, in turn will increase oil temps due to the piston oiling jets.

Not sure it should have dropped that much, but keep in mind, the oil will thin with increased operating temps..... I've seen it on a few of my rigs that I have been "pushing"......

I have been running aux gauges on my rig for nearly 18 years. I watch them both. So driving home on the local freeways I kept seeing a red flash on my dash down low on the drivers side. Finally caught it on long enough to see it. My oil pressure was dropping on my factory dash gauge. Seemed my isspro electrical 270 degree sweep gauge was reading fine. So I drove on. Turns out my sender had failed. Because our engines create so much vibration many times electrical connections loosen and they break up the messages they are designed to be sending. Our water in fuel connection under the fuel filter and the oil pressure sender connection are famous for this. Remove the wire. Squeeze with a pair of pliars and install. Fixed it..

snicklas said:

That being said, on a long haul, with high RPM's like that, the oil will thin out as it gains heat. Which at 3000 RPM, you would be putting a lot of heat in the heads, which may increase coolant temps, but you will also be putting more heat into the pistons, which, in turn will increase oil temps due to the piston oiling jets.

Not sure it should have dropped that much, but keep in mind, the oil will thin with increased operating temps..... I've seen it on a few of my rigs that I have been "pushing"......

Click to expand...

We have an oil temp gauge, fully loaded and pulling a long grade foot to the floor with the coolant at 230 and oil like 50-60 above it the pressure still held up decent. So yes, heat buildup in the oil is a factor, but the effects from it are not quite so severe.

Our engines have AWESOME oil pumps. They have 8 internal oil leaks (piston cooling jets) form the factory. The pumps are gear driven off of the crankshaft. No weak hex shaft to break (6.2/6.5). As long as the engine is running and has enough oil, you should never lose oil pressure despite what the factory gauge says. I like mechanical gauges for my trucks.

do the factory piston cooling jets have a valve in them like modern engines do, where they dont open up untill 20 psi or so? or do they just bleed all the time?
LCAM, 280-290 oil temp is HOT! I am not familiar with the properties of diesel specific oil we run, rather gasser only, but at those temps the oil adn additives are severely breaking down and oil is coking.
That being said, these engines have been running at 230F fully loaded up grades for the last 30 years and they seem fine. Like I said, I dont know much about diesel oil.

My factory gauge gave me a scare. Would occasionally drop to zero. Replaced the sender and no change. Put a mechanical gauge in there and it stays where it should be.