Just purchased a 95 FLHR Road King. I've noticed pressure drop as engine warms up @ idle & @ low rpms slowing from highway speeds to town speeds (idiot light). After reading a few threads, I purchased an oil pressure gage, installed & became more concerned. Read a few more threads, am somewhat confused. Most say this is common not to worry. Some get into detail that sparks worry.
A little info, pushing 57000mi., bike runs great, no unusual noises, plenty of power. Pulled relief valve & spring to make sure they weren't stuck. Same with check valve spring & ball. No visual abnormalities. Ran back to normal op mode, pressure drops. On highway, @ 50-60mph for about a mile, gage reads 0-10, but light goes out.

When does this become a big enough concern to get it checked out?
Also, any other possibiles I can look for would be much appreciated

 

As a engine wears clearance between parts oil will leak out of those parts at a faster rate causing oil pressure to drop.

Also a worn oil pump will not move enough oil to develop enough oil pressure at low speeds.

This is why your engine has good pressure when cold. As the engine warms up oil flows thinner and will leak out faster, so pressure drops.

This is why at highway speeds your oil pump is being turned over at enough rpms to have oil pressure, slow speeds and idle the oil pressure drops.

This indicates you will be needing an engine rebuild of some sort.

Sometimes a new old pump will help. Usually doesn't.

This is why the bike was sold by the previous owner.

Edit to add: If bike is not needed your primary transportion you can leave it for a winter project, or just nurse it along until you can't put off a rebuild.

 

I don't know about a '95 model, but my '07 will run around 32 lbs. of pressure rolling down the road. Sometimes it's a bit less if it's real hot out and I don't have the rpm's up around 2500 - 2800.

 

Try running straight 50w or 60w oil and see how you do. With the 60w allow an extra minute or two at startup before you gas it.

 

When peace of mind becomes more important than the money saved by not getting it checked.

 

Dont panic, you don`t need to overhaul your engine.

Is the idle RPM too low? This is a common cause for the idiot light to illuminate at idle.

The wear items that will affect oil pressure on a Harley are the clearances between the lifters and the lifter blocks, the rocker shafts and rocker arm bushings, and the clearances in the oil pump. That`s it...

Despite what 32vld says, the condition of connecting rod bearings has nothing to do with oil pressure on a Harley, it does not use plain bearings like an automobile, it has roller bearings.

 

Actually, as parts warm up, clearances should DECREASE as parts expand to fill gaps.

 

On your Evo if the oil light comes on when you turn on the key and then goes out when you start the engine then your bike is making at least 5 to 9 psi idling. My repair manual says 5 psi minimum to turn off the idiot light and 12 to 35 psi at 2000 rpm. That is considered normal. Most of the people I know with Evo's see 10 to 25 normally when warm. I have never seen 35 psi on my Evo even in it's puppy years. Twin cams run higher oil pressure and should not be confused with Evo's. Do not idle these bikes down to simulate a cam lope as I see some do. My advice to you is to ignore the pressure gauge or look at it like an additional piece of chrome----if you can't do that then throw it away. All it is doing is making you paranoid. An oil pressure light that stays on and top end rattle is a problem.

 

Thanks for input. I do believe engine is still in great shape. Runs great, no noises. I'm just not sure which way to go now. I feel that warning lights are there for a reason, not to be totally ignored. However, it seems to be running fine, despite a little paranoia. Straight 50wt oil had been suggested to me, but I was more interested in fixing problem than hiding it. Maybe that's not the intent, just my interpretation. Putting myself out there,... what next?

 

From evos on back to the beginning of time, HD used ball or roller bearings. They do not need pressure per se, they just need oil on them. Thats why the oil pressure can be so low and not hurt anything. There are a few plain bearing surfaces, not badly affected by low flow. As airboater says, continuous light and top end noise is cause for concern. Try draining a quart and putting in a qt of Lucas Heavy Duty Oil Stabilizer. Great stuff that helps with dry starts, lubrication, noise, and pressure. My only Evo went 151,000 without a rebuild at 22 psi normal cruise and about 3 at idle. Having the light come on is a little abnormal, but can be caused by a switch out of tolerance. That said, this statement confuses me: Does this mean that after a mile the pressure goes up to 12-25, or does it drop, or what? At what rpm? Or, if no tach, in what gear at 50-60?