When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello - recently purchased a 04 Z06 with 50K miles on it. It is my first Corvette and my 1st post.
Changed the oil and filter and experienced a low oil pressure indication that night, but with a few seconds the oil slowly came up to 40psi. Now, as some background only had the car a few days so don't necessarily know if it was there before or not. Did test drive a week prior to purchase and have inspected independently as well and no indication of the issue. Oil was noted dirty so changed it at one of those quickie places(read enough threads now to know don't do that again).
Action 1:
Took it in a second time to a more reputable service shop and put Mobil 1 5W30 and they put in a ProSelect filter. Problem of slow oil pressure rise still there.
Action 2:
Took it to a corvette shop and they replaced the Oil Pressure Sending Unit. Drove it home and upon a several restarts with 30 minute spacing it had a slow enough oil pressure rise to alarm, but cleared itself within a second and rise up.
Under normal driving conditions oil pressure goes up and down with rpm's. Typical cold start would be 45psi.
Extended idle with 215 Oil temp could come down and settle 15-20 at 650rpm and then rise to 30+ when cruising at 1800 rpms.
Have rerouted the Oil Sender and included a manual gauge into the line up to help verify of this intermittent issue is real or electrical/wiring related. One observation is that the manual gauges comes up much faster than the instruments do.
Was able to reproduced the low oil pressure and observe the manual gauge was in fact low as well, but both came up within a second of that.
Problem appears to be real. I'm of the mind that changing the oil filter with a Mobil 1 or PF46 could still be the fix, but from what I read there is a whole host of things it could be, but was hoping there is logical way to rule out certain things. Open to suggestions and ideas.
Thanks
Last edited by Jcrankshaw; 07-09-2016 at 06:39 PM.
I've run royal purple 5-30 in my car before, that stuff is thin at temp. At 200+ oil temp my pressure would register maybe 23-25. With German castrol it sits around 32-35 at 200+ oil temps.
Even with the royal purple at 200+ degrees I have never gotten a warning from my dic. The oil pressure has been instant (2-3 seconds) Given that Mobil 5-30 is between German castrol and Royal purple viscosity wise it sounds as if you have an actual oil pump pressure issue. I've read somewhere before about a pressure bleeder valve on the oil pump that can fail. I won't talk about something I'm unfamiliar with though. Regardless it sounds like oil pump replacement will be your solution.
A healthy pump shouldn't take any considerable amount of time to build pressure regardless of the oil or conditions. Only bandaid solution I can think of is just verifying that the oil filters your installing have an anti drain back valve in them.
If everything was normal, you would get a higher oil pressure on a cold start and then pressure should decrease as the oil warms up. Sounds like something is blocked. You said that the oil was dirty when you bought the car; could it be that the PO hadn't changed the oil in a long time? If the pump/oil galleys are all sludged up, that might be it. It might be worth a couple of cans of oil treatment before you tear into the engine.
Synthetic oil shouldn't sludge up, pull a valve cover to verify though. Maybe run some sea foam in the crankcase, 1 oz per quart. It won't break down the oils lubrication properties and will help clean it up. I doubt this to be the problem though but you never know.
Update: Tried some seafoam. Figured it couldn't hurt as next step may be to replace oil pump which probably means oil change as well.
Drove about 8 miles to store and returned. Engine temp was a hot as 232.
Some pressure numbers during ride home. AT 218 Oil Temp: 650 rpm = 15psi and at 35psi at 2000 RPM.
At 225 degrees Oil Temp: 38 psi at 3000 RPM
Home idling at 650 RPM, 14psi, but what is concerning is manual gauge is reading only 8 psi.
Definitely a problem just not sure about the root cause yet. Time for the shop though before driving further.
What is curious to me is the intermittent nature of it or is the problem really a constant problem that just appears intermittent with the low oil pressure warning?
Thanks for the input and if anything comes to mind to help narrow down the search let me know.
Like I mentioned before it may be the pressure relief valve or the o ring on the pick up tube. Your pressures seem fine with 35# @ 2000 rpm. The general rule of thumb is 10# per 1000 rpm.
Also not many people know this but a lot of oil filled gauges aren't as accurate in the bottom and top 20% of their gauge scale.
You've said your problem isn't oil pressures once it's at operating temp but it's from cold start up and building oil pressure. Your start up oil pressure should be in the 30-40s at idle WHEN COLD. That is where the concern is.
It maybe something as simple as a slugged up pressure relief valve though, which is in the oil pan.
Last edited by Nasbluec5; 07-10-2016 at 05:52 PM.
Reason: Clarifying
Trying to think about it logically though if say for example the pressure relief valve is stuck open at idle when cold that would create a pathway for the thick, cold oil to go instead of taking the path of greater resistance throughout the block. The oil pressure sensor/gauge is at the top of the block. Therefore it would take awhile for the oil pressure to build throughout the motor.
Say for example on my car if I get on it while the oil is still cold my pressure gauge will peg itself. 70-80# oil pressure instantly.
If your car cannot create that same scenario then logic tells me pressure is being relieved somehow. Not a whole lot that can happen to a physical oil pump aside from some gears stripping out.
Now once the car is warm and the oil is thinner the oil pump can overcome this leak because even if the relief valve is sticking open the resistance between the oil pumping through the block and the leaking valve would be similar.
First things first!
If it were ME,,,,,,,,,, I would install a MECHANICAL gage in the front drivers side of the block and see how that responds compared to what you are seeing.
The port is below #1 plug and a little forward on the side of the block.
I had to do this when I had a ZERO pressure indication after a heads cam/oil pump change. It ended up having excellent pressure and the problem was ELECTRICAL.
The mechanical gage cleared that up instantly!
I would also remove the oil filter housing and see if there is anything wrong there!
Last edited by Bill Curlee; 07-11-2016 at 10:46 AM.
Update - Oil Pressure confirm to be zero or slow to rise with mechanical by me as stated and also by a shop. They say they hear noise, but it does not sound noisy to me anyway but that does not mean much since this is my corvette.
May do a 3rd oil filter swap with Delco PF46 just for one last ditch effort.
Beyond that:
One approach is to drop the pan and verify pickup tube etc..
Nothing there then remove oil pump and look to see if relief valve is sticky.
This has some cost to it obviously or an alternative would be to drop engine and trouble-shoot from there with the reasoning that it could be cam bearing related.
Since a shop is doing it there will be a decent amount of money for labor.
My question is the following: Say I try to the pan-oil pump combo and it is no go in terms of resolving the intermittent low/slow oil pressure at start.
Now have to tear into engine to solve the problem. I assuming there is already bearing damage at this point and so what would be the cost ramifications of driving the car knowing the bearings or something causing the low/slow intermittent oil pressure build up?
At that point could I just delay the engine re-build, use a thicker oil like 10W-40 and drive the car knowing an engine repair is in order at some point? As long as there is > 10psi pressure at warm idle it is technically within spec of GM so why not save up some money and then opt for engine swap?
Update - Oil Pressure confirm to be zero or slow to rise with mechanical by me as stated and also by a shop. They say they hear noise, but it does not sound noisy to me anyway but that does not mean much since this is my corvette.
May do a 3rd oil filter swap with Delco PF46 just for one last ditch effort.
Beyond that:
One approach is to drop the pan and verify pickup tube etc..
Nothing there then remove oil pump and look to see if relief valve is sticky.
This has some cost to it obviously or an alternative would be to drop engine and trouble-shoot from there with the reasoning that it could be cam bearing related.
Since a shop is doing it there will be a decent amount of money for labor.
My question is the following: Say I try to the pan-oil pump combo and it is no go in terms of resolving the intermittent low/slow oil pressure at start.
Now have to tear into engine to solve the problem. I assuming there is already bearing damage at this point and so what would be the cost ramifications of driving the car knowing the bearings or something causing the low/slow intermittent oil pressure build up?
At that point could I just delay the engine re-build, use a thicker oil like 10W-40 and drive the car knowing an engine repair is in order at some point? As long as there is > 10psi pressure at warm idle it is technically within spec of GM so why not save up some money and then opt for engine swap?
Personally if you have the funds for an engine build I would just build the motor. You have no idea what damage could be or is done without tearing into it anyways. You'll get a dozen opinions but this is just mine.
It'd be silly to spend a grand or more on doing all the investigative troubleshooting when you can put it towards a fresh motor build.
Would you take the tact of rebuilding the exiting motor, making the assumption that it probably it not too damaged and is worthy of a rebuild effort?
Personally I feel the block should be fine. If it's not making any bizarre noises it probably will just need new bearings and rehone the cylinders, maybe some oversized Pistons. Have you found any ferrous or non ferrous material in the oil filters?
Update: Oil filter changed to a AC Delco, probably a PF46, but will confirm. Mechanic noticed that it seemed to go from 40psi average on cold start idle to 43psi and that it idled at 25psi warm, but didn't note the temperature. Don't have high hopes, but maybe that is really enough to make a low oil pressure warning at start go away. Is is possible that with tolerance stack ups that this engine is just on the high side of the clearances and therefore runs lower oil pressure than average?
Update: Ok Mechanic started and moved around all day Saturday, started it Sunday and today and did not note any more low pressure issues and drove around got it warm up and thought it may be okay. Obviously, not sure but stated it seemed better than before oil filter changed from a engine sound point of view. Anyway, unfortunately drove it home let it set for an hour started it up it was slow to build pressure with low oil pressure alarm for a second before oil built up an alarm went away. Weird how it happens right away for me.
Readings are from a days driving with multiple starts. Just for completeness there have been several zero oil pressure starts where pressure does not build. Usually a restart and it comes up. Normally, it starts and come up to pressure but frequently it starts and low pressure warning, but comes up within several seconds. If a cam bearing has spun wouldn't the oil pressure be more contant and not have the longer zero oil pressure starts versus the pressure relief spring in oil pump being weak or slightly stuck open?
Had shop attack pickup tube, o-ring, and oil pump as I had another day where there was zero oil pressure on multiple starts and figured it was most likely not a CAM Bearing issue, so decided there was a high probability this may solve the problem, assuming there were not two problems going on. Lucked out and it worked!!! Now have at 220 oil temp idling around 750 rpm 25psi versus 15psi and now no warning message at startup in 3 days of driving.
Look at amount of blockage compared to the tube diameter, covers a large percent.
I'm having similar problems...this is mine, any advise would be sincerely appreciated. On start up, zero oil pressure for about 10-15 sec, then normal. If I start the car with it pointed up hill, zero oil pressure until flat or going down a hill then normal. Hilly driving etc. normal oil pressure. I don't think it's the pump, and I've had the sending unit replaced. I'm thinking that it may be that o-ring. Thoughts? TIA -- Leroy
I'm having similar problems...this is mine, any advise would be sincerely appreciated. On start up, zero oil pressure for about 10-15 sec, then normal. If I start the car with it pointed up hill, zero oil pressure until flat or going down a hill then normal. Hilly driving etc. normal oil pressure. I don't think it's the pump, and I've had the sending unit replaced. I'm thinking that it may be that o-ring. Thoughts? TIA -- Leroy
Your best bet is to install an analog gage in the aux port just forward of #1 cylinder spark plug. That will give you a real time pressure reading .
If it truly is LOW,,,,, I would look at the O ring at the pump/suction tube joint and also look at the pick up screen for blockage..
07-09-2016, 06:37 PM
Intermittent Low Oil Pressure on Start
