Oil Pressure Light

Last weekend took the ST1100 out for a couple of 250 mile days getting ready for an up coming riding vacation and the bike ran like a top no problems. Monday headed to work on the ST and a mile from the house the Oil Pressure light flickers then a quarter mile later the light comes full on. So I pull off and listen to the motor before shutting it off and it sounds ok. Checking around the bike to see if maybe I had a major leak, or holed the pan or some other reason the light might come on but found none. So put the bike on the dual stand and started the bike watching the sight glass to see if oil was being picked up (oil leaving the sight glass) and it was, I also opened the filler cap to see if the top of the motor was getting oil and it spit oil out of the filler hole. With all this I felt safe riding the bike back to the house.

One I was back at the house I let the bike cool, and then again started the bike, watched the oil drain out of the site glass and check the oil filler to see oil was making it to the head. The bike has 98,000 miles on the clock and less than 1000 miles on the most recent oil change (rotella syn, purolator filter) and the oil level was middle of the glass so I did not think it was an issue with oil or levels.

With this information figured that I had a faulty Oil Pressure Switch so ordered one and installed tonight, and the light stayed on after starting the bike. I again pull the switch and tested it with low pressure air and the switch functioned correctly (also checked the old switch and it was ok). Then I started the bike with the switch removed and the bike pumped oil out of the hole for the switch so I knew the switch was ok and oil was being pumped to the switch.

So my final test was to install the switch, start the bike, then bring the revs up to see if this affect the light at all, and it did, the light went out just above 4000 rpms so with the results it looks like I might have low oil pressure (at least I have oil pressure) which I would guess is a pump issue. I dont have any equipment to test the actual oil pressure so it looks like the pump is pumping but the pressure is not enough to trigger the switch (unground the switch). From reading my manual looks like it might be a stuck pressure relief valve or a pressure value spring.

Looking for some advice to validate my thoughts and to see if there are any other possibilities or things I might try to remedy the issue. Are there any other oil screens in the lube system (other than the filter) that might plug, or could a there be an issue with the oil filter that could cause low pressure?

Thought about changing the oil and filter to see if this would have any affect but maybe just grasping at straws with that move so might wait to see what the group thinks.

Really interested in how bike could do the 500 miles over the weekend then with in a mile of the house have a pressure issue.

Any help you could send my way would be appreciated as it looks like pulling and replacing the oil pump is a very involved project with having to pull the clutch to get the pump out, plus if I was in that far I would just replace the pump instead of rebuilding. Plus this points to having to change bikes for my trip which I hate to do as my ST is the travelling bike in the garage.

Again thanks in advance.

Greg D.
STOC906
2001 ST1100
1995 ST1100 RIP

I think I'd try changing the filter first in case it was defective, or the pressure relief valve in the filter was wonky.......good luck.......ff

I would also change the oil and filter as that is an cheap fix if it turns out to be the problem. Good luck.

I'd second the oil filter.

What kind of oil filter did you use?

Update, this morning I did an oil and filter change (rotella syn (5-40 blue jug) with Purolator Gold filter (type I have been using for years)) and received the same results. Oil light stays on after starting, oil pulls down out of site glass and oil still making it up to the heads (squirting out of filler when open).

Guess next step is to go down and get a standard oil pressure gauge and plumb it into the switch port to see what actual pressure is, but all that will most likely do is show me that the pressure is low.

Does anyone know what the presure needs to be to trigger the switch, can not be much as the specs on the ST say that the pressure at 5000 rpms should be around 50 to 70 psi. It took up to 4000 rpms to have the light shut off so Idle pressure must be too low but if I knew the amount to trigger switch it would tell me how low.

Again thanks in advance for any help

Greg
STOC906

Could be (the bike) pressure relief valve stuck partially open.
Internal oil leak.
Worn pump (too much clearance)
Clogged suction strainer.

I guess the strainer would be the easiest but pressure check sounds like your next step.

I would try a gallon of Rotella T5, 15W40 and see if the light goes off. You could try it without even changing the filter. For about $13, you could find out if 5W40 is too thin at idle RPM's.

John

Nashcat said:

I would try a gallon of Rotella T5, 15W40 and see if the light goes off. You could try it without even changing the filter. For about $13, you could find out if 5W40 is too thin at idle RPM's.

John

Click to expand...

If 5W-40 is to thin at idle you have problems.

Pull the connector from the oil pressure switch ( with the ignition ON, bike not running ). Does the light go OFF ?? It should. Then ground the pin in the connector. The light should be ON now. If those checks are good, maybe the replacement oil pressure switch is funky ?? Or maybe the passage that the switch screws into is partially clogged. That would limit the pressure at the switch. You could remove the switch and probe the passage to see if it's gunked-up.

BTW, if the oil filter bypass was open, that would increase the oil pressure, not decrease it. But if the pressure relief at the oil pump was stuck open, that could cause the problem.

I seriously doubt you have low oil pressure. You probably would have seized the engine by now or you would have some serious noises, at least.

Usually the switch IS the problem.

BuddingGeezer said:

If 5W-40 is to thin at idle you have problems.

Click to expand...

I've never had a problem with the low oil pressure light coming on when I'm running 10W-40 oil , BTW.

Well a follow-up/close out for my Oil Light issue. Finally had time to tear into the ST to see if I could determine any visible problems but everything looked clean with no metal in the pan so after all the testing I moved on to plan B.

Went ahead and ordered a new oil pump, all the necessary gaskets and O-ring, a new pickup screen, pressure switch and finally since I had to pull the clutch, a new set of clutch springs. Total order from Service Honda came out to be around $350 (few extra parts added since I was placing the order).

Disassembly went well, after filing off the retention tab on the large clutch nut I used a impact gun to spin off the nut. Removed the oil pump drive sprocket, then pulled the oil pump with little trouble. Then reversed the process installing the new pump, o-rings, sprocket, and clutch basket.

When it came to torqueing down the large clutch nut I made a tool to hold the basket from turning as putting it in 5th gear and holding the brake just was not working. The tool was patterned off the one built by a fellow ST owner ?Wanderlust? (Jim from CA) that I read about while researching how to remove the clutch as one piece. You can see the tool in 5th post of the following thread.

https://www.st-owners.com/forums/showthread.php?3746-ST1100-Clutch-Replacement

Buttoned everything up, installed the new pressure switch, filled the bike with oil and fired it up with my fingers crossed. Bike fired right up and within a few seconds the oil light went out. It was then time to crack open a cold one and let the bike warm up to see if there were any leaks or problems. After 20 minutes everything looked great so replaced all the bodywork and took it for a run the following day. I have put about a thousand miles on the bike since the replacement of the pump and no issues.

I have tested out the original and replacement pressure switch and both work within spec, the electrical system for the light tested out so the issue had to be with the pump or the pressure relief valve that is part of the pump. One of these days I will pull the pump apart to see if I can figure out what was wrong as I do not like not really knowing what was causing the issue but now it?s time to ride.

I wanted to send this follow-up for everyone who offered advice to say thank you for your help and the time you took responding to my messages. With your help another ST1100 stays on the road and starts its journey towards its second 100,000 miles.

Again thanks and we will see you on the road.

Greg D.
STOC906
2001 ST1100
1995 ST1100 RIP

Thanks for the feedback. And Wow, I'm surprised you did 500 miles with low oil pressure without an engine failure of some type.

Before you replaced the oil pump, did you disconnect and ground the oil pressure sending unit electrical wire ? If you did, did the oil light go off ??

Got to say, it's hard for me to understand how the oil pump could be "worn out. Could be a sticky pressure relief valve as someone mentioned. I keep wondering if something else was done to cure the problem when the oil pump was replaced. But if you dissasemble the old pump, you might see what was causing the problem, or if you can't find any problem with the old pump, it will add more puzzle to the story. But I think the pressure relief valve, which is part of the oil pump is the main suspect

No Jim, I had ridden the bike 500 miles the day before with no issues (no oil light) and then the following day as I was heading to work just a mile from my house the oil pressure light came on. I did test the oil pressure light, wiring and even the actual pressure sending unit and all were fine. I am also figuring that the issue was with the pressure relief valve on the pump but that part is not available by itself, it comes as an assembly with the pump.

There is really nothing else that would have been cured replacing the pump as it is a simple matter of pulling the part and replacing and other than the clutch nothing else is removed from the engine except for the pump.

Once I have some time I will pull out the snap ring pliers and pull the pressure relief valve out to see if the spring is broken or the valve is just stuck. if the spring is not broken it will be hard to tell as the little valve might have closed up since it has been removed.

For the cost of the pump and a few of my hours of labor it was a small price to pay to get her back on the road.

Well kscyckist, I'm a new guy here having the exact problem you have described, and I am wondering if you can give a follow up. Have you had anymore problems since you fixed the bike?
I don't know the spec for the switch, but I pulled mine and it opens reliably at 1.9 psi, cold or hot. I am an aircraft instrument technician and have a full compliment of calibrated test equipment at my disposal. I have installed a pressure gauge temporarily on the bike but not had much chance to road test it that way yet. I'll have plenty of opportunity to do that this weekend. Planning to replace the pump very soon.