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Old 07-01-2014, 01:38 PM   #1
Improbus
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Default Oil Pressure Fluctuation with Temperature and Humidity Increase

In your guys experience, is it normal to see a 2-8 PSI difference in oil pressure when the ambient temperature and humidity increase? I did some searching and saw a lot of different opinions on this topic. I'm running Motul 5w-30 Eco-Energy and a Purolator PureOne PL14660 filter on my 2011 WRX for full disclosure.

Every summer my oil pressure dips down to 10 PSI or so at 700-800 RPMs when I have the clutch depressed and coast with it depressed or I am stopped. Under boost and normal driving, the pressure is within the acceptable ranges outlined in the service manual ~80 PSI under full boost and between 70-80 PSI cruising at 3k RPMs, and around 100 PSI on cold start. Oil on the dip stick is always at the hole or notch.

I have my sender hooked up to a braided line that uses the NPT Fitting near the turbo because I wanted to keep the stock sender hooked up as well. Any information or knowledge would be appreciated, thanks in advance.
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Last edited by Improbus; 07-01-2014 at 01:57 PM.
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Old 07-01-2014, 02:41 PM   #2
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At idle there will be a drop in oil pressure when the oil is warmer. You notice the oil drop 10psi in the summer because its warmer outside so the oil is warmer than what it would be in winter.

As temperature goes up the thinner the oil gets (up to an extent) and with the low rpm (idle) the typical car engine is not rotating fast enough to produce higher oil pressure
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Old 07-01-2014, 02:42 PM   #3
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If you read your oil temps and pressure in winter and in summer youll notice that the temps increase and pressure decrease (again up to an extent)
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Old 07-01-2014, 02:50 PM   #4
Improbus
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hungrymonkey27 thanks for the input I appreciate it. I understand that oil thins as temperature increases but I was unsure about how much of a difference that would make on a pressure reading but from what you have stated a 2-8 PSI difference is within an acceptable range. Thanks again for the input.
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Old 07-01-2014, 05:09 PM   #5
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Never saw less than 20 psi even when oil is in the 230~240F range (so, yeah, pretty hot). I'm using M1 0W40 at the moment and my sender setup is identical to OP (NPT fitting bolted to galley port next to turbo, going into a braided line and to sender).

EDIT: seems like OP is "stage 2+" and I'm not sure Motul 5W30 Eco-Energy is the best choice.
It seems like a robust oil but it was designed for fuel economy.

Last edited by neg_matnik; 07-01-2014 at 05:22 PM.
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Old 07-01-2014, 05:16 PM   #6
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Mine is never below 20psi either. Mine is setup under the alternator in the stock location. Im using t6 5w-40. 10psi seems kinda low even for 5w-30 in the summer.
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Old 07-01-2014, 05:29 PM   #7
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I think we need Dennis / bluesubie's input on this one.

Datasheet of Motul 8100 5W30 Eco-Energy here: http://www.motul.com/system/product_...pdf?1357580406

Seems like it meets Renault's RN0700 standard but this standard is only good for their N/A engines and 100HP or less 1.5L turbo Diesel engines.
It seems like this oil wouldn't work for any of the N/A or turbocharged Renault Sport engines.
To me, this means it's no good for a souped-up EJ255/EJ257.
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Old 07-01-2014, 05:38 PM   #8
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I'm doubtful it's the oil itself. The gauge reads same with OEM filter and oil and read same with no mods.

I'm also a religious 3k oil changer.
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Old 07-01-2014, 05:42 PM   #9
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If its been dropping like this for a few years and you havent had any problems then it should be fine I guess.

I wouldn't put that oil or any energy conserving oil in my car for that matter but thats just my preference.

Mine drops from about 25psi to 20psi at idle in the summer for reference.(on warm motor).
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Old 07-01-2014, 06:20 PM   #10
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Quote:
Originally Posted by meinct View Post
If its been dropping like this for a few years and you havent had any problems then it should be fine I guess.
Yeah I've just always been a bit speculative about the issue/quirk. I've never had any engine issues and I monitor Feedback Knock closely with my AccessPort and have never had a problem.

Oil on the dipstick is always good, and I've never needed to add oil between the 3k changes. The car has been Stage 2+ for ~30k miles at this point.

It is a Prosport Gauge and I know some people have had issues with the gauges and sending units so perhaps I will consult them and see what they think.
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Old 07-01-2014, 06:31 PM   #11
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Could be. Im usin a defi for boost and oil pressure and I have never had any problems.
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Old 07-02-2014, 09:59 AM   #12
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I am currently having email traffic with Kyle from Prosport. He believes the gauge isn't receiving enough amperage to report the proper readings from the sender. He has provided some troubleshooting steps which I will perform this week and report the outcome. I wanted to keep everyone informed in case anyone else is having a similar issue.
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Old 07-02-2014, 01:19 PM   #13
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Quote:
Originally Posted by Improbus View Post
I am currently having email traffic with Kyle from Prosport. He believes the gauge isn't receiving enough amperage to report the proper readings from the sender. He has provided some troubleshooting steps which I will perform this week and report the outcome. I wanted to keep everyone informed in case anyone else is having a similar issue.
Yes, make sure you have a ground wire between the sender and the chassis (or the engine block itself). I think the braided line between the sender and the engine block can't be relied upon to provide a good ground.
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Old 07-02-2014, 01:34 PM   #14
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Yeah. My plan of action is as follows.

1. Disconnect the Oil Pressure Gauge from its current power source.
2. Run the new wiring harness with some alligator clip test leads directly to the battery to see if the gauge behaves properly by being powered by the battery directly. If it still is not functioning properly then I will get a replacement.
3. If the gauge is grounded properly and the battery test works, I plan on rewiring the gauge via some fuse taps to the following fuses.

Constant 12v - Fuse # 3 - DOOR LOCK
Switched 12v - Fuse # 26 - IG2
Illumination/Dimmer - Fuse # 16 - ILLUMINATION

If that doesn't work I'll replace the sending unit and if all else fails, I'll get a gauge from a different company. Good news is, its nothing mechanical or engine related.
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Old 07-02-2014, 11:00 PM   #15
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Prosport gauges are pretty but not very accurate. I have 3 Halo series and the egt gauge reads hot by a good margin. The other two are suspect. You get what you pay for. I'm keeping them because they aren't mission critical gauges and at least provide me with a relative point of reference. And did I mention how perty they are? My oil pressure and boost gauges are Greddy and are spot on. And ugly lol
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Old 07-03-2014, 10:51 AM   #16
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Oil pressure does not only fluctuate with temperature, it varies with the second set of numbers of the oil rating, after the W.
A xxw50 vs a xxW40 will increase hot idle oil pressure, for the same oil temperature by close to 8 PSI. if you use a xxW40 instead of your 30, you'll probably land close to 18 PSI.
However, if your idle pressure would be 14 PSI at 176F, you'd land over 20.
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