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oil pressure fluctuation at high rpm?

Old 10-13-2018, 05:45 PM
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Default oil pressure fluctuation at high rpm?

my car has had this issue for a while.
at high rpm the oil pressure gauge will fluctuate and drop 1-2 bar. this only happens at high rpm (6k+)
car is running a older boundary engineering oil pump assembly. it has a mocal oil cooler thermostat adapter plate and dual oil coolers up front.
the car has had this issue for a long time, and it does not eat bearings. no metallic particles in the oil and its been running 400+ whp for years.

Wires from the oil pressure gauge have been checked/replaced and it otherwise works fine. im not sure how to go about fixing this, but i would be more comfortable if it didnt have this issue

any ideas or experiences ?
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Old 10-14-2018, 02:50 AM
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Originally Posted by hf-mx5t View Post
my car has had this issue for a while.
at high rpm the oil pressure gauge will fluctuate and drop 1-2 bar. this only happens at high rpm (6k+)
car is running a older boundary engineering oil pump assembly. it has a mocal oil cooler thermostat adapter plate and dual oil coolers up front.
the car has had this issue for a long time, and it does not eat bearings. no metallic particles in the oil and its been running 400+ whp for years.

Wires from the oil pressure gauge have been checked/replaced and it otherwise works fine. im not sure how to go about fixing this, but i would be more comfortable if it didnt have this issue

any ideas or experiences ?
There are some vibration harmonics that mess with the internals of he stock electric sender that mounts to the block. A fully mechanical aftermarket Gage won't read those fluctuations. Remote mounting the stock sender also seem to make it go away as well. Some spec Miata companies sell kits that run a line from the block so you can mount the sender to the chassis and isolate it from the vibration of the engine block at high rpm.



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Old 10-14-2018, 10:13 PM
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Pump is cavitating. Melling has some graphs on this.

Did a few data logs showing this with the Miata pump, LS3 pump and LS7 drysump.
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Old 10-15-2018, 03:13 AM
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is this a common problem with the old na8 boundary engineering pumps? would it be a good idea to get a new pump or would this still be the issue on those?
this car has been running for many years on the same pump, so if i could replace the pump and get peace of mind and see a stable oil pressure i sure would do that
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Old 10-15-2018, 04:57 PM
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Spoke with a couple of oil pump manufactures at the PRI show and its just a normal thing with oil pumps driven at crank RPM. Miata-GM LS ext.

Does not seem to be much of a problem on the Mazda motor as there are a zillion of them being hammered to death in many forms of racing.

As long as flow/pressure does not fall below threshold your motor needs? Remember your pump makes flow. Restriction & viscosity make pressure. Cavitation-foam reduces viscosity quickly.

One engineer did comment it could be a factor in stock cast/powdered pump gears giving out.

Can be mitigated a bit with oils that foam/cavitate less like Amsoil, Joe Gibbs ext. as well as optimizing hot on track viscosity. Its all a balancing act.
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Old 10-15-2018, 05:44 PM
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Is this on the stock gauge or an aftermarket gauge? Because the stock gauge tends to go wonky at high rpm sometimes. I assuming you have an aftermarket gauge but just thought I would ask.
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Old 10-15-2018, 05:56 PM
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this was on the stock gauge, in the process of connecting up a new pressure sender to my mini dashlogger
I THINK that my car actually has oil pressure.. since it has not blown apart even after a long time and running well over 400whp. but ill have to doublecheck. If i still get the same reading on a different gauge, what could cause this ? not enough flow from the na8 oilpump(i dont have VVT so it should be enough) ?
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Old 10-15-2018, 06:06 PM
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Originally Posted by hf-mx5t View Post
this was on the stock gauge, in the process of connecting up a new pressure sender to my mini dashlogger
I THINK that my car actually has oil pressure.. since it has not blown apart even after a long time and running well over 400whp. but ill have to doublecheck. If i still get the same reading on a different gauge, what could cause this ? not enough flow from the na8 oilpump(i dont have VVT so it should be enough) ?
My guess is the stock gauge is off, get an aftermarket gauge on it and I bet it shows normal.
I would think that pump would cavitate at very high rpms, are you revving past 7400 rpm? If you are maybe the stock pump is having trouble keeping up at the higher rpm.
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Old 10-15-2018, 06:44 PM
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im not revving really high, i have the limiter at 7600 but i see this fluctuation well before that.
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Old 10-16-2018, 12:09 AM
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My stock oil pump gets pushed past 9000 and the is no oil pressure fluctuations in my logs or on my aftermarket gauge. Good pressure (ie more than 50PSI) is fairly critical at high revs otherwise the bearings will fail rapidly. Given that your bearings are still alive at 400whp I'm guessing it's just the stock gauge failing rather than an actual pressure dip.

Also as a side topic, oil pumps in wet sumps tend not to cavitate unless they are sucking air like a dry sump pump. Oil by itself won't boil to a vapor as quickly as water so you actually need air bubbles trapped in the oil that will expand to cause cavitation. I also run a sump baffle because under very high braking G's I was seeing an oil pressure dip. That means the pickup was sucking air partially due to the oil moving forwards in the sump under brakes and also that more oil was being trapped up in the head due to the higher revs. It's not normally a big problem in a turbo miata because you guys aren't high in the revs when the pressure dips happen, but when you are money shifting to 9000 rpm the big end bearing load is at it's highest load right when that air is being pushed through the bearings. I only noticed the dips once I was running aero and slicks and then a few laps later I did a big end. Since the rebuild and installing a sump baffle I'm now pushing more G's under brakes and I'm not seeing the same dips in oil pressure.
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Old 10-17-2018, 04:43 PM
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Connected a additional pressure sensor to the ECU and did some logging today. low boost pressure due to slippery roads but still a good test.
The stock gauge dropped a lot at high rpms like before, but the pressure logges as violet line in the ecu shows stable oil pressure all the way to the rpm limiter in 2-3 gear.

Looks like i need to change the stock pressure sensor.

Thanks for the tips guys.


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Old 10-17-2018, 05:53 PM
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Originally Posted by hf-mx5t View Post
Connected a additional pressure sensor to the ECU and did some logging today. low boost pressure due to slippery roads but still a good test.
The stock gauge dropped a lot at high rpms like before, but the pressure logges as violet line in the ecu shows stable oil pressure all the way to the rpm limiter in 2-3 gear.

Looks like i need to change the stock pressure sensor.

Thanks for the tips guys.

I wouldnt even use the stock pressure sender, I would just get an aftermarket gauge that will be more accurate anyways. Good to know the stock gauge was incorrect.
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Old 10-17-2018, 06:32 PM
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thats why the new gauge sensor was connected to the ecu so i can display it on the dashlogger
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Old 10-17-2018, 11:49 PM
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I dont see the point of getting an aftermarket gauge if you have a miata with a "real" gauge. It still shows a pressure that you can use for reference.
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Old 10-18-2018, 03:16 AM
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For a car that sees track time I think the only priority gauge to have is a good oil pressure gauge. I have a Longacre Accutech SMI with 3 stages of warning lights and I've stuck fluro markers onto it for cold idle pressure, and target hot pressure. I use a second oil pressure sensor to run for my engine safety which I rely on to drop the ECU into limp if pressure drops. I basically monitor the oil pressure gauge over time so that I can tell if my engine is down on pressure which can tell me if the oil needs changing or there is a larger issue etc. It's really only there for startup and quick checks during the warmup / cooldown to see where the pressure is sitting and that I'm not getting dips (LED flashes) on hard sustained braking. Once I'm at full pace I really don't have time to look at any gauges other than my lap time delta. I have ECU logs I can check if I'm looking for oil pressure dips, oil temp, coolant temp etc etc.
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Old 10-18-2018, 11:17 AM
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Originally Posted by sshamrockk View Post
I dont see the point of getting an aftermarket gauge if you have a miata with a "real" gauge. It still shows a pressure that you can use for reference.
Because as this thread has already stated its inaccurate rendering it basically useless.....
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Old 10-18-2018, 12:12 PM
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its not useless. if it worked properly i could atlease see that i have oil pressure. but now i have this logged in the ecu with warning in the dashlogger, but i would still like to fix it so i can have the stock gauges not scaring me
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