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Low oil pressure at idle

29K views 21 replies 7 participants last post by  CanyonRider 
#1 ·
I have a 2004 Mazda 6 wagon V6 with 122k miles. Recently the oil light started flickering on and off. Eventually it got to a point where at operating temp it was on all the time at 1500RPM and below. Mechanic put a gauge on it and said it is reading 10PSI at idle then jumps up to 25+ once above 1000 to 1500RPM.
He was not sure whether an oil pump would fix it or whether it could be internal seals which would be a big job to investigate and fix.
1) Is 10PSI too low at idle?
2) could this just be a bad sensor?

Any other suggestions are appreciated!

Thanks

Pete.
 
#2 ·
Yes. 10psi is too low.

I have a very accurate mechanical oil pressure gauge with 270deg sweep in my 6. At cold startup it idles between 90-100psi. Under hard driving conditions it varies from 30-70psi. At hot idle it sits at 20psi.

CR
 
#3 ·
Odds are that you have bearing clearance issues. It MIGHT be the oil pump, and on some engines it's reasonably cheap and easy to change it. I'd probably do it simply because if that's not the issue you're looking at a complete tear-down and at that point for most cars you begin to think about engine replacement instead.
 
#4 · (Edited)
What weight oil are you using? If its a 20 weight step up to a 30 weight and see what the oil pressure is then.

Idle oil pressure doesnt have to be very high to keep the engine protected since there is very little load on the bearings. On my VR4, Mitsubishi says the minimum oil pressure at hot idle is 11 PSI. in most cases as long as the oil pressure rises at a rate of at least 10PSI per 1000RPM you are safe.

Edit: I should state that I still dont like to see oil pressure that low at hot idle, even if the manufacturer says its safe.
 
#5 ·
Sludge could also cause low oil pressure.

If you have a good engine I would then remove front valve cover and check for sludge or burnt oil. If there is sludge then check the pickup screen to see if it is clog or sludge. This can reduce flow into the oil pump and cause low oil pressure.

I would check for compression wet and dry to see if you have a good running engine before do anywork.
 
#7 ·
The oil pan was dropped fairly recently due to a bad pan gasket, so there is not sludge in there. Looks like the bearing issue is most likely unless the pump is bad, but I hear this is not as likely.
I am using 5W-20 so I will try stepping up to 5w-30. can I go up to 5w-40?
 
#8 ·
Just because the pan was dropped doesn't mean the screen on the pump intake was inspected, unless YOU dropped it and looked.

And yes, this IS a potential issue. I've seen a number of Audis with this problem; it's common in those cars and a new oil pump (with a new and clean screen, of course) fixes them right up.
 
#9 ·
With excessive bearing wear I would assume rod knock or engine noise. If you don't have low oil level, no sludge and clean oil screen, and pump is good it might be the oil sending unit.

It could be gasket at the oil pickup or oil pump is bad. It could be oil pump gear is just worn. Then replacing the oil pump and gaskets is no issue.
 
#10 ·
Thanks for the advice. The mechanic that did the oil pan gasket replacement specifically said that he cleaned everything in the pan and I have been using this guy for years, he is very honest and thorough! I would assume that the pump screen would be part of that clean up but I will check with him. There is no knocking or abnormal engine noise.
My dilemma is that I was planning on replacing this car in the next 12-18 months and don't want to put a lot into fixing it up, but I also do not want to blow an engine.
Would a good plan of attack be to switch to a heavier weigh oil first and see if that helps, then change the oil pump?
 
#13 ·
Decided to try a heavier weight oil and some motor honey as I was due for an oil change. Put in 5W 30. Still the same problem.
One thing I did notice when driving was the the longer I drove, the higher the rpm was when the light came on. After 40min drive, light was coming on at 2000rpm instead of idle.
mechanic confirmed he cleaned everything when the pan was dropped so a clogged oil pump filter should not be the cause.
still no bad noises, running fine. I would think pressure switch if he had not hooked up a manual Guage and got the 10psi reading at idle.
any suggestions on other causes based on the fact the light comes on at a higher rpm the longer the car runs?
 
#14 ·
Yeah, bearing clearances probably, or possibly a stuck or malfunctioning pressure control valve in the oil pump. The latter is reasonably cheap to fix (change oil pump) the former is, of course, not.

The reason the pressure goes down the longer the car runs is that the viscosity goes down the hotter the oil gets. Oil temperature doesn't stabilize for a good 10-20 minutes after a cold start (coolant temp stabilizes quite a bit more-quickly.)
 
#15 ·
Interesting development today - on my way home from work - the oil lght barely came on at all - even at idle - just barely flickering. Wondering whether the heaver oil was taking effect, but that was 75 miles ago.... earlier today it was coming on as before at round 1250RPM and staying on.
I bought a replacement pressure switch just to see if that was the culprit. Doubtful as a manual gauge was reading 10 PSI at idle, but some people have said that the light does not come on until 3-4PSI....
I am going to attempt to change out the switch out tonight, even though I know it is a nightmare to get to....
 
#19 ·
Very interesting. I have the same symptoms you've had and had my mechanic test the oil pressure and he said it was 10psi or too low. I wonder if he got a false reading or something since it looks like you had the same thing said to you. My motor is running great with no ticks, knocks or smoking. Lots of power and smooth as can be. I really hope it's the pressure switch.
 
#20 ·
For reference, I have a mechanical oil pressure gauge in my car. At cold startup it reads 90-100psi. At hot idle it reads 40-50psi. It fluctuates dramatically on the track with RPM, but never drops below 30psi. I'd say 10psi at idle is too low.


FWIW, I still have the oil pressure switch connected and it has never come on while the engine was running.


CR
 
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