Oil Pressure Question

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Aug 17, 2003
Boise, ID
Hey guys need some insight on an oil pressure question. I have a 2003 Nissan 350Z. After completing the engine breakin with DINO oil (using Bosch oil filters) I switch to Mobil 1 5W-30 as per the owners manual recommended weight.

Still using the Bosch oil filter, I have noticed that my oil pressure (with M1) is about 15psi higher at cruising speeds and about 30psi higher at redline then it was with DINO oil.

According to my service manual the oil pressure is measured between the oil pump and oil filter.

The oil filter is getting nice and hot so it seems to be getting oil flow, but I have not tried replacing it yet. My questions are:
1. What would cause this large pressure increase?
2. Does increased oil pressure in this case mean more or less oil flow volume? Or is the flow volume the same but the oil filter may go into bypass mode sometimes?

Thanks in advance
That's odd, if anything the oil pressure should have dropped slightly with M1 at idle do to it's ability to flow better. I would install a new oil filter just incase the one you have on there now is defective some how.
Don't know your exact rpm's, but as a rule of thumb, oil pressure should advance 10 psi per thousand rpm. If this isn't in the ballpark, then try a new or different filter. Some engines are pickier than others when it comes to oil and filters.

[ September 26, 2003, 11:07 AM: Message edited by: Schmoe ]
Interesting, I have been lurking on this site for several months now with no real reason to post. Using the searches and such, I came up with most of the answers I needed. Still don't know about oil analysis yet, but that is another whole story.

I also have a 350Z that I recently switched to Mobil 1 5W-30 and put a larger Napa Gold 1356 (from the 2000 Max) cause I wanted a larger oil filter than the coffee can for the 350Z. Well, I also noticed an increase in oil pressure, although not quite as drastic as Z Licious states.

Our stock oil pressure gauge is real sensitive, more sensitive than I have seen in most cars. They really didn't dampen the gauge much. When the car is cold, and you rev it high, of course the gauge goes to its max output relatively quickly.

As for how much the increase on mine is, I would say it is about half of what Z Licious said. When I first changed it, it was a higher change, how long ago did you change yours Z Licious?? Now I have around 2500 miles on the oil, and I usually get 8-10 psi higher on regular cruises and 15 psi at the redline.

I am also like him in the fact that I am not sure this is a good thing or a bad thing. Some say more pressure means more restriction, but I don't know. Our stock oil filter is small with carboard caps, and is really a pretty badly designed filter. Maybe the increased effiency and/or filtering ability of the Napa filter made the pressure go up, but that is just a theory from a newbie (with a Chemical Engineering degree).

[ September 26, 2003, 02:09 PM: Message edited by: Deep_Freeze ]
Yeah, I am running an oversized Bosch filter as well. Maybe that is part of the issue?

I have about 3000 miles on the oil and filter so far.
Here is what I am seeing for pressure according to the gauge in the car (when fully warm)
idle: 28psi
2000rpm : 58psi
6000rpm : 110psi or so.

I am going to try a different oil filter brand and see what happens. It bothers me that when I get near redline with the engine the oil pressure pegs the gauge. That can't be good.

[ September 26, 2003, 02:18 PM: Message edited by: Z Licious ]
Well, dude, I don't think it is bad, but I am not an expert, YET, lol. The factory Nissan filter is crap. Using a filter like a PureOne might increase the oil pressure simply cause it is filtering out more contaminants. I just can't see how more filtering is bad. I haven't checked RPMs, but I will take a look at it today. This is not an uncommon thing, mind you, other Z owners have reported increased oil pressure by just switching to synthetic oil alone, even while using the factory Nissan oil filter.
If the sending unit is between the pump and filter and by changing the filter you get more pressure, that means the filter is more restrictive. Not a good thing.
I agree that the filter is more restrictive since it has a high amount of filtering medium. The Bosch filter is basically the Mobil 1 filter but at half the cost. The factory oil filter is a Fram piece of crap.

Now just because the filter is more restrictive does not mean the flow has decreased (but it could). The oil pump will pump a certain volume of oil through the engine regardless of pressure so long as the oil pump's pressure relief valve is not tripped.

My main concern is when running the engine at high RPM and my oil pressure gauge is pegged at max. I am not sure where the oil pump's relief valve kick's open. I am just worried about oil starvation at high RPM.

I am going to try a couple other brands of good filters and one cheap one and see what happens. I will post results here on Monday.
Anyone ever consider "pump slip" or "efficiency" when playing around with different filters and oil brands/weights?
The oil pump will NOT pump a certain amount of oil 'regardless' of pressure, restriction, viscosity, or temperature.

Most OEM oil pressure gauges are nothing but extravagant idiot lights. Get a quality aftermarket gauge(hopefully mounted after the filter if possible).

Doesn't the FSM list the oiling systems specs? oil pressure regulator opening PSI?....

Another thing to consider is oil temp. A synthetic, in most applications that I've seen with temp gauges, will usually lower the temp of the oil. Is it possible that the Mobil1, even though a thin oil for its weight, is at a higher viscosity because of lower average oil temp?

Also consider windage/aeration. I'm betting that a synthetic will stay together and not whip into shaving cream. The mineral oil might be bubbly at higher rpms, and might not drain down as quick which could lower the oil level at the oil pump pickup causing the oil pump to turn into an air pump.
I experienced similar results after switching to Amsoil 15W40 Marine oil and filters on my boat. Is this a common occurance? Anyway to determine if the flow is reduced or not?
In a high performance engine, I'd rather see a person use an oil filter that catches only the rocks and birds, and lets the small stuff, along with the oil through.
Or, use a full flow and a by-pass set-up.
In order of importance: oil first, clean oil second.
Brand, base oil group, and all of that, are a way down the list of priorities IMO.
Lucky for the Nissan motor its oil pump by-pass is not set for 45LBS.

Originally posted by userfriendly:
In a high performance engine, I'd rather see a person use an oil filter that catches only the rocks and birds, and lets the small stuff, along with the oil through.

This is my theory too, which is why I use the K&N oil filter on my Firebird, since I love to go full throttle as often as possible.
OK, so you guys are saying it is a bad thing? Well, I do know that it has been reported by most Z owners that switch to synthetic, that the oil pressure increases. And this is with the same factory oil filter. So are we saying no synthetic?? After some research here, I thought the Napa Gold oil filter was one of the better ones for the cost, am I wrong and should I consider something else??

I don't know, but I am considering on adding a turbo, so this oil pressure issue is an important one to me.
One thing that no one seems to have hit on here. This is ONLY a change in the oil ...not the filter (if I read this correctly). That is ..same pump ..same filter ..same rpm ..same engine ...DIFFERENT OIL. Everyone here is discussing the "more restrictive filter ..trash it and get ?????).

Your engine must have some effect on dino that is not realized with Mobil 1.

I am, of course, open to other schools of thought ..but this IS NOT a filter issue. It may be cured by one (if you even look at this as a bad thing _ I don't).
110 PSI at near redline is fine. Most modern engine designs bypass bdetween 110-180 psi with an average of 150 being the most widely used bypass seting.

It is true that filters can case an increase in pressure and decrease in flow. I doubt that the Bosch is causeing any problems though. The Bosch is made by Chapion Labs which also makes most Delco filters, STP, Car and Driver, K&N, Tech2000 andmany other brands.

My moms Tundra runs up to 158PSI before bypass I belive and my Dodge Dakota also ran past 150 before bypass. My Dodge ran 110 psi at 2500 RPM's. Oil pressure is generaly a good thing.

Check with all data and see what normal pressure is and where bypass starts. If you have a service manual it sould say in it as well.

If you think it is filter and you have 3000 miles already on a relatively new engine I would just change the oil and filter. The Tech2000 filters are known to flow well. If you just want to swap out filters then try one of them they are cheap.
I agree with Patman and others, oil flow and pressure first, then clean oil.

I think what is happening is that the synthetic oil is not shearing in the oil pump as did the dino. Shearing causes viscosity decrease, which results in reduced pressures.

As long as the overpressure valve in the filter adapter is working, I say you're ok.

158PSI before bypass I belive and my Dodge Dakota also ran past 150 before bypass. My Dodge ran 110 psi at 2500 RPM's.

Wow ..you people are quoting some REAL INCREDIBLE oil pressures! Are YOU SURE you're not reading kilopascals ..or some other metric equivalent? My 4.0 DC/Jeep has a 58 lb pressure relief ... only exceeded while accelerating when it's stone cold.

The only reason that I find this pecular is because most aftermarket (even most hi-performance - Autometer PRO COMP for one) gauges ..only go to 100. The Boss 302 and the Camaro Z28 (70 1/2 I think) had the distinction of blowing apart the factory oil filters when shifting at 7000 rpm due to hitting such high pressures. The FRAM HP1 and HP2 were used on these engines (I believe repackaged).

I'd sincerly (this is me) worry if I had anything as "common" as an off the shelf oil filter on my engine if I routinely experienced such high pressures.

The only thing that comes close to a "sensible" equivalent is "inches of mercury" (it isn't only used for vacuum), where my 58 psi limit would be approx 118 +Hg and the typical 0-80 psi span works in the ranges that you people are operating in.

This is NOT a sale link: conversions

[ September 27, 2003, 04:02 PM: Message edited by: Gary Allan ]
Patman, we experience these oil pressures normally, they are just a little higher now. I also wanted to point out that I am running the larger Napa Gold filter instead of the coffee cup filter that comes stock for the Z. I also stated that many other owners of the Z that have switched to synthetic have noticed an increase in oil pressure without switching from the coffee can filter. I said this to make sure that you guys know that while I have increased oil pressure, people are getting increased oil pressure from just the synthetic oil.

In my case, I got the oil and a different filter. Don't really know if my increase in pressure is more or less than the people who didn't change the coffee can filter. Because I have a larger filter, I am worried that my oil pressure difference is even more, but I am not sure of this.

Nissan does say in the manual that they advise to only use dino oil, but who listens to them.

[ September 27, 2003, 05:57 PM: Message edited by: Deep_Freeze ]
I'm not saying that there is a problem here, but I'm just adding that my 95 Firebird's LT1 engine doesn't go much higher than 40-45psi at full throttle and 5700rpm redline. Even when cold the pressure is never over 60psi. But every engine is different.
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