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Gauge change with altitude?

Gauge change with altitude?

(OP)
I have an oil pressure gauge that seems to read consistently different while driving at 4,500 feet as compared to driving at 100 feet ASL. (Above Sea Level) Does this make sense?

That's only a 2.2psi difference in altitude but the pressure difference is greater than that; 50~55psi at sea level and
40~45psi at 4,500ft.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Gauge change with altitude?

Your oil cooler and radiation are less efficient at high altitude and the oil temperature may be higher.

RE: Gauge change with altitude?

Yeah, there's a lot going on when trying to measure the difference between what happens at sea level vs a mountain pass. Be careful to keep everything the same so your observations are valid. Temperature and pressure are the most obvious one, but there are others.

RE: Gauge change with altitude?

Your altitude compensator may not be not working. They can clog sometimes.

RE: Gauge change with altitude?

yes, altitude compensators, usually located near the widgets...

All joking aside as others have said there are many things involved
1) was the oil temperature the same (different temps = different viscosities)
2) assuming you are driving "sportingly" your oil is likely substantially hotter when you get to the top then when you started at sea level
3) bearing clearance also change as the engine heat soaks, if clearances increase and the oil is thinner ==> less resistance for the oil to squeeze out from between the bearing and journal, i.e. lower oil pressure

and many more

RE: Gauge change with altitude?

Actually there were "Alaska Compensators", those little plaques they put on some of the gages on construction equipment on the North Slope that indicated what the gage was supposed to read before you put it to work in the cold.

RE: Gauge change with altitude?

Consider how low cost those engine gauges and senders are. Yet how rugged they are. And how well they continue to work considering they experience the cold of winter and the heat of summer year after year with no calibration.

And, you want it to be accurate also? I'm just happy the little pointy thing continues to move somewhat like I expect!

When I want my expensive bench meter to be right I have to keep it at around 20C and still have it calibrated yearly.

RE: Gauge change with altitude?

(OP)
Good points that enough oil pressure is enough oil pressure so exactly what it is may not be all that important.

I recognize all the variables thermal and otherwise.

The case I'm asking about is same engine temperature same highway speed both level ground nothing else different except altitude. These differences are seen while doing weeks of "daily driving" at the two different altitudes. That's why I listed the ranges (50~55psi and 40~45psi), these are the ranges seen doing the same type driving but at different altitudes.

Since these are both just daily drives with the same sort of ambients I'd expect the cooling system to keep the same engine temps since the loading is minimal.

Probably the biggest difference is the turbo. It may be running hotter at altitude? Heating the oil more? Temp/viscosity..

Keith Cress
kcress - http://www.flaminsystems.com

RE: Gauge change with altitude?

The oil temperature isn't thermostatically regulated and can vary widely even with a constant coolant temperature.

RE: Gauge change with altitude?

Well, it can be. I have a Mazda RX-7 air cooled oil cooler with built in thermostatic control in my hobby car.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Gauge change with altitude?

hemi, what does the thermostat do, change a fan speed, or open/close a duct damper, or ...?

RE: Gauge change with altitude?

meters oil flow through the cooler vs bypass the cooler
very much like a radiator thermostat

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Gauge change with altitude?

Should you not be seeing higher gauge pressure at higher altitude? There is lower atmospheric pressure against which the gauge must act. The gauge measures the differential pressure of oil to atmospheric.

Ted

RE: Gauge change with altitude?

Oil pressure should be the same at altitude. The pressure relief valve that controls oil pressure is referenced to ambient pressure and therefore maintains constant gauge pressure not absolute.

je suis charlie

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