oil pressure rise. Causes?

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Jan 13, 2007
Orange, NSW
Can anyone think of a situation that would cause the oil pressure to rise in the engine..? Did about 400km yesterday, on dirt roads at a reasonable speed and my oil pressure rose dramatically after about 250km...

All fluid levels are fine, oil is fressh (2000km old) and the outside air temperature although probably 30-ish 'c was no higher than the truck has coped with before.

The only thing i can think of is that the constant vibration of going over the road ruts has knackered the oil in the sump, thinning it drastically and causing the pressure to rise whilst pumping. The last 75km wsa done after dark, with temperatures dropping to low teens and during this time the pressure did lower a little from where it was in the hotter part of the day, but it was still higher than normal. I have never seen the gauge move before; ever.

I am going to change out the oil and see if there is a difference. Any other ideas?

the only reason i can think of the pressure rising would be: you are using a thicker oil, there is blockage somewhere after the pump, or your gauge is malfunctioning, or maybe the voltage regulator on your alternator is going causing high voltges(youd see other gauges reading high though too)

Maybe change the oil and check for metal particles.
Not meant to hijack and excuse the 1/2 :banana: question, but what are the causes of the exact opposite problem. Oil pressure high/normal under regular conditions - Extemely low on freeway?
Hmm... I work on a mine site and brought the truck up here to continue on a tour of northern WA next week after my stint. On the day that the oil pressure rose we went through a lot of standing water on the mud tracks around this area.

I didn't mention this at all to the workshop leading hand, but he suggested that it maybe the switch shorting out and that did we encounter any water...

I have arranged for them to have a look at the vehicle tomorrow when they have a bit of spare time, so i'll report back. Fingers crossed its nothing more serious than that; otherwise it will be a stripdown of the sump, etc.

low pressure could be any of the above reasons as well. If there is blockage before the sump it could cause low pressure, after it would be high pressure. If you dont have oil spraying out of something and theres oil on the dipstick than the problem is probally with your gauge or with your sump.
pressure relief valve in the pump?
bad oil filter?

i'd change the oil and filter and then check oil pressure with a mechanical gauge. if you have good oil pressure with the mechanical gauge but your dash gauge doesn't jive, then you at least know that you have a sender, wiring, or gauge issue.

what kind of RPMs were you running when you noticed the high reading of the oil pressure gauge. higher RPMs usually mean higher oil pressure; up to a point anyway.
The workshop looked the vehicle over and decided that the oil pressure sender (down by the filter) was water logged and shorted out. This sent a spike to the guage. They think everything is working as it should otherwise.

They've covered the sender in denso tape, so i'm not bothered to undo it any time soon as that stuff gets everywhere.

The guage is back to reading more or less normal, its just very slightly above the normal position. The workshop suggest this is because the spike warped the bi-metallic strip in the gauge itself and that i would need to replace this to return the reading back to its exact original location.

Having a look under the bonnet, there is a few muddy splashes around the oil filter (don't have wheel arch protectors on the car so engine bay is open to splashes from the tyres), so it seems plausible enough to me. The oil still looks good (2,000km old) and no funny noises. Will keep eye on it on my big trip next week and i have spare oil & filter with me just in case.


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