Low oil pressure at idle when car is warm

[slowSho21]

I've been driving my 1989 sho for about 4 months now, and for the first 2800-3000 miles it was all fine. I daily drive the car, about 75 miles per day, alot of highway. But then I started getting this issue and did an oil change about 3 weeks ago. Since right before the oil change and up until now, whenever I drive the car and it gets warm I end up getting a low oil pressure light at idle. Anything above 1500 rpm and it seems to go away but it makes driving in traffic a pain. Let me know if anyone knows what I should do. I checked oil when I got where I was going today and it was full. I know the car burns oil pretty good but I think I've only put maybe 400-500 miles on the car since the oil change because I switched back to my Subaru once the weather got cold. I just check and fill the oil every time I fill up on gas so it never gets very low. Any help or advice would be appreciated, I'm gonna try to get a measurement to find out exactly how low the oil pressure is at idle I'll update this here once I do it

 

[zoomlater]

I've been driving my 1989 sho for about 4 months now, and for the first 2800-3000 miles it was all fine. I daily drive the car, about 75 miles per day, alot of highway. But then I started getting this issue and did an oil change about 3 weeks ago. Since right before the oil change and up until now, whenever I drive the car and it gets warm I end up getting a low oil pressure light at idle. Anything above 1500 rpm and it seems to go away but it makes driving in traffic a pain. Let me know if anyone knows what I should do. I checked oil when I got where I was going today and it was full. I know the car burns oil pretty good but I think I've only put maybe 400-500 miles on the car since the oil change because I switched back to my Subaru once the weather got cold. I just check and fill the oil every time I fill up on gas so it never gets very low. Any help or advice would be appreciated, I'm gonna try to get a measurement to find out exactly how low the oil pressure is at idle I'll update this here once I do it

it could be you need a new sensor, do you know if it was ever change before? On one of my cars I had the light come on and then it would go off after I brought the revs up. After a awhile, the light just stayed on. I am pretty my oil sensor is the original and needs to be changed (this started happening after I just changed my oil). Hopefully it's not a bearing issue, how many miles are on the car?

Oil Pressure Sensor Unit

Anyone changed an oil pressure sensor unit? 1990 SHO. Looks a little hard to access, since it is up behind the axle shaft, high on the engine . Any special tools or advice on how to do this? I have an unusual issue, the dash light still works, but the plastic nose of the sensor unit will...

shoforum.com

 

[rubydist]

First thing to do is to put a real gauge on it, so you know what the pressures really are. The sensors do go bad, and they are old now, so more of that type thing will begin to happen. But, the rod bearings wear and then have too much clearance and that bleeds oil pressure, so it could be a real issue, and you might need new rod bearings. That is very common on these engines - about every 100 - 150k miles to replace those. Of course it could be something else too, but those 2 are by far the most likely causes.

 

[Irish Pride]

The cheapest and quickest thing to do would be to replace the oil sensor on the back of the engine. Being an 89 it will be easily accessible from under the car.

I had a 91 that started having an oil light while I was on a weekend vacation in the mountains. I kept the revs up while I was driving and tried not to put myself in any situations where I had to sit still in traffic. Actually took the car on Tail of the Dragon on the way home. When I got back home I changed the rod bearings. The bearings looked worn but not bad. All back together the light was still coming on. Swapped the sensor and the light went away. Smh.... I'm still glad that I did the bearings so I could show that it had been done when it came time to sell the car but it would have been a lot faster to start with the sensor.

-Chad

 

[clayb226]

After you verify the pressure, main bearings will cause low oil pressure after warmed up.

Sent from my SM-S236DL using Tapatalk

 

[Irish Pride]

After you verify the pressure, main bearings will cause low oil pressure after warmed up.

Sent from my SM-S236DL using Tapatalk

These engines are not known for Main Bearing wear. The Rod Bearings are the weak link.

-Chad

 

[clayb226]

These engines are not known for Main Bearing wear. The Rod Bearings are the weak link.

-Chad

I have read this, but in my experience, the main bearings have caused this issue in many vehicles.

Sent from my SM-S236DL using Tapatalk

 

[rubydist]

Every one of these that I have had open, even with close to 200k miles on them, all had perfectly fine main bearings. The rod bearings, however, especially on the mtx cars, can be toast by 100k miles.

 

[sperold]

There is a real push for light viscosity oils in the last 10 years or so. That is not great for an older engine with perhaps some wider clearances on the bearings.

These engines are low pressure / high volume oil systems by design.

My best results for my 89 were obtained by using 10 W 40 grade regular (not synthetic) oil, and changing it every 2000 miles. I nursed my 89 along for years using that procedure.
And yes, the oil light would come on at an idle after a 120 mile ride, but there were no ill effects from this condition. And like you, I raised the idle RPM while sitting at lights.

Try the oil pressure sender first (I had one that failed) and try the higher viscosity oil if yours is nowhere near what I used. I did not have to raise the RPM to 1500 to get the light to shut off, just above idle did it for me.

If the above instructions do not work out, I would consider new rod bearings as I understand it can be done with the engine still in the car. But I suggest you can pick your time to suit your schedule, like mid summer.

 

[SalukiSHO]

There is a real push for light viscosity oils in the last 10 years or so. That is not great for an older engine with perhaps some wider clearances on the bearings.

These engines are low pressure / high volume oil systems by design.

My best results for my 89 were obtained by using 10 W 40 grade regular (not synthetic) oil, and changing it every 2000 miles. I nursed my 89 along for years using that procedure.
And yes, the oil light would come on at an idle after a 120 mile ride, but there were no ill effects from this condition. And like you, I raised the idle RPM while sitting at lights.

Try the oil pressure sender first (I had one that failed) and try the higher viscosity oil if yours is nowhere near what I used. I did not have to raise the RPM to 1500 to get the light to shut off, just above idle did it for me.

If the above instructions do not work out, I would consider new rod bearings as I understand it can be done with the engine still in the car. But I suggest you can pick your time to suit your schedule, like mid summer.

is there any known way to simply raise the oil pressure at idle? I know there is the oil pressure bypass trick with washers in the pressure bypass valve, but that only raises the max pressure, not the idle pressure.

 

[rubydist]

No, the issue is with the relatively larger clearances in the SHO motor, it takes a lot of volume to keep the pressure up, and there is not that much volume at idle. So, raising the idle speed increases the volume and therefore helps avoid the oil light coming on.

I personally never used heavier than 10W30 oil in any of my SHO engines, I would change rod bearings when needed. Its really not hard to do in the car, just annoying that oil will be dripping on your head as you are working under there...

 

[slowSho21]

Today I finally got around to putting an oil pressure gauge on the engine and got some numbers. Cold start at idle the engine makes almost 60 psi. Seems good to me. Pressure stayed steady through the revs and never dropped. After a drive to get the oil warm, I had about 14 psi at idle (about 900 rpm) and at 1500 rpm the engine made about 34. I believe that the sensor is just inaccurate because the spec for the idiot light is supposed to be around 7 psi. I will be ordering a replacement soon. Thank you all for the help and replies. Let me know if anyone has any opinions about what oil pressure you should have at idle.

 

[SalukiSHO]

Today I finally got around to putting an oil pressure gauge on the engine and got some numbers. Cold start at idle the engine makes almost 60 psi. Seems good to me. Pressure stayed steady through the revs and never dropped. After a drive to get the oil warm, I had about 14 psi at idle (about 900 rpm) and at 1500 rpm the engine made about 34. I believe that the sensor is just inaccurate because the spec for the idiot light is supposed to be around 7 psi. I will be ordering a replacement soon. Thank you all for the help and replies. Let me know if anyone has any opinions about what oil pressure you should have at idle.

are you sure it was fully up to temp? Mine typically will rest around 11-13 psi at idle once FULLY warmed up, like just drove around for a while and then let it sit and idle for a while too. I actually hate that the oil psi is so low on these cars. Seems like such a dumb design, rod bearings, while they are a wear item, should not be considered "routine maintenance" in my opinion. Especially not before 200k miles. I understand thats the nature of these engines but I want to know what the Yamaha people were thinking when they decided on the whole "high volume, low psi" oil system...