Didn't pay attention before last weekend me and wife were on a nice day ride on our 15 Limiteds as I watching the air temp and oil pressure on my bike as I exceeded 85 mph the oil pressure dropped couple psi and as slow down to 80 it was up couple psi, tried few times and same result then ask wife on the CB to compare and speed has opposite effect on her bike speed increases so the oil pressure. Not sure if the sending unit is inaccurate on my bike or oil pump getting confused with higher RPMs have an appointment next week but am expecting the answer from the HD tech that it's normal and within HD guidelines.

 

Oops I meant SPEED.

 

I am no expert, however my opinion is that your oil pressure is more closely related to RPM's , not speed. Maybe try a run while looking at RPM's instead of speed

 

Yes I'm aware of that but constantly having higher RPM is more possible at higher speed on the hwy and that's where oil pressure was dropping as RPM were increasing and staying at it for a longer at higher speed it will drop and as I ease off the throttle and drop the speed few mph as rpm also drop by few 100s pressure will go up instead other way around.

 

Thinking out loud: All things being relative on the two bikes, the cam plate has a bypass spring/valve that tries to maintain some specific pressure based on the spring strength.
If say, your oil filter is older/dirtier than hers, maybe your pressure is higher which kicks on the bypass which drops your pressure or something.

Or your bike has better tolerances or less or was hotter or colder or maybe your oil is newer or older or...

Or maybe it's just messing with you because it knows you're looking at it? lol Heck I dunno.

 

I dont have a rushmore bike, but had the same experience this weekend on a 1000 mile ride over mostly freeway.

given that i was on the bike approx 17 hours over two days and most of the ride was high speed, i had the opportunity to try a few process elimination ideas out.

I started from the simplest to the more complex. Here they are in order,

Sending unit plugged in and not loose. process, plug and un plug sending unit. Outcome no change. continued fluctuation

checked wiring going into the sending unit. process , re-arrange harness, straighten wires out outcome - decrease in the amount of oil pressure fluctuation, but no elimination.

Oil level - process, checked oil level at fill up. oil level at low end of acceptable added oil to put level at mid point on dip stick outcome no change

oil filter - process, stopped at HD store bought new filter, spun old filter off, installed new filter. Cost $9.00 (black filter) outcome, elimination of majority of fluctuation

Conculsions out of all these experiments, doubtful, plug wiring or oil level was affecting pressure, indicating problem was mostly related to oil filter as replacement eliminated the problem.

Once i got home, I cut the suspected oil filter apart to check for metal or issue, Outcome none. No large metal chunks, or apparent filter issues. One identifiable issue was K&N filter vs Stock HD. microns on K&N 10, HD supposedly 5, but who knows.

this could have been the issue, will need to conduct experiment in reverse to validate results.

variables not tested cam plate, (have gear drive cams and 15% basiley spring) so suspect it is probably not mechanical.

oil pressure gauge.


your results may vary, my conclusion, will change oil (napa 10W-60 pure synthetic) and install another new HD filter in approx 1000 miles to determine if this indeed eliminated the problem

 

What pressures were you getting? Mine will run 30 when warm and after some constant higher speed on the freeway, I'll see as low as 25 but usually 27-29. A lot has to do with oil temp and sending units will vary.

 

32 to 35, oil temp at approx 225 to 230

Drop down and fluctuations were in the 28 to 30 range, same oil temp.

Avg speed 80 to 85

Built 107

Oil pressure was always higher when oil temp was below 200

Outside temp was 60 ish

I have lowers and 10 row vertical jag

Ive owned the bike 11 years. I know its habits really well.

 

It rarely drops below 30 going 85 otherwise 33-34 cruising at below 80 mph in ideal weather, haven't ridden this one in 110 plus AZ weather yet but it's coming soon, grand kids birthdays are coming this summer when it will be miserably hot. Those months wife flies but I ride don't care for those low ceiling narrow body airplanes.

 

I'm no expert but I would suspect it's related to the fact that oil filters will bypass once the demand exceeds the flow rate of the paper element.