Can hot weather cause lower oil pressure even when oil temp is the same?
07-06-2009, 06:59 PM
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Can hot weather cause lower oil pressure even when oil temp is the same?
Just curious... does hotter ambient temps affect an engine's oil pressure even if the actual oil temp is similar?
My car runs about 210 oil temp when fully up to temp on the street (no hard running). It runs the same in the summer and winter, but I've noticed over the past couple of weeks w/ the temps in the 90s my oil pressure is a bit lower at hot idle.
Oil is fresh Mobil 1 5w30.
My car runs about 210 oil temp when fully up to temp on the street (no hard running). It runs the same in the summer and winter, but I've noticed over the past couple of weeks w/ the temps in the 90s my oil pressure is a bit lower at hot idle.
Oil is fresh Mobil 1 5w30.
07-06-2009, 07:37 PM
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Re: Can hot weather cause lower oil pressure even when oil temp is the same?
So I'm probably not going to say anything that you don't already know, but that doesn't usually stop me..
I first thing that comes to mind is hotter engine temps, which can affect bearing clearances, etc., and that can change the oil pressure. Oil is going to be a certain viscosity at a certain temp, and that will change depending on how long the oil has been in the engine obviously (dilution and shear and all that stuff). BUT if the oil passages and bearing clearances are changing size because of differences in temp, oil of the same viscosity can have different galley pressure. It's also possible to have hotter oil in areas that are far from the oil temp sender, and then have the oil at lower temps as it passes through areas of the engine that are very well regulated for temperature. Basically you are measuring the temp of oil travelling through the engine, but not necessarily measuring the temp of ALL the oil in ALL areas of the engine. So some hotter areas in the engine in hotter weather may have hotter local oil temps that don't show up as well, or have only a small contribution to raising the average oil temp that the temp sender is reading. So pressure in those local areas could be different in hot weather.
The temp-based pressure effects are very similar to pressure effects from bearing wear; it's all just changes in clearances..
So I'm assuming that you're comparing oil pressure at the same idle RPM, and the hot idle RPM isn't higher/lower than what you're comparing to?
Could be something as simple as a small change in oil filter design too, which tends to happen every once in a while.
Fresh oil is a big factor though, so are you comparing the oil pressure to the dirty oil that came out or just the usual clean oil pressure after your oil changes?
Is that a murky enough answer?
I first thing that comes to mind is hotter engine temps, which can affect bearing clearances, etc., and that can change the oil pressure. Oil is going to be a certain viscosity at a certain temp, and that will change depending on how long the oil has been in the engine obviously (dilution and shear and all that stuff). BUT if the oil passages and bearing clearances are changing size because of differences in temp, oil of the same viscosity can have different galley pressure. It's also possible to have hotter oil in areas that are far from the oil temp sender, and then have the oil at lower temps as it passes through areas of the engine that are very well regulated for temperature. Basically you are measuring the temp of oil travelling through the engine, but not necessarily measuring the temp of ALL the oil in ALL areas of the engine. So some hotter areas in the engine in hotter weather may have hotter local oil temps that don't show up as well, or have only a small contribution to raising the average oil temp that the temp sender is reading. So pressure in those local areas could be different in hot weather.
The temp-based pressure effects are very similar to pressure effects from bearing wear; it's all just changes in clearances..
So I'm assuming that you're comparing oil pressure at the same idle RPM, and the hot idle RPM isn't higher/lower than what you're comparing to?
Could be something as simple as a small change in oil filter design too, which tends to happen every once in a while.
Fresh oil is a big factor though, so are you comparing the oil pressure to the dirty oil that came out or just the usual clean oil pressure after your oil changes?
Is that a murky enough answer?
Last edited by Fabrik8; 07-06-2009 at 07:39 PM.
07-06-2009, 07:53 PM
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07-06-2009, 08:12 PM
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Re: Can hot weather cause lower oil pressure even when oil temp is the same?
Oh, so I guess that the best test would be to check the oil pressure at hot idle when it isn't hot outside, like late at night...
But yeah, failing oil pump.. LOL..
j/k..
But yeah, failing oil pump.. LOL..
j/k..
07-06-2009, 08:18 PM
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07-06-2009, 09:16 PM
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Re: Can hot weather cause lower oil pressure even when oil temp is the same?
dude i so had my vette read lower pressure for a little while, thought nothing of it, my oil pump eventually failed..bad news
it failed racing a Ferrari F50, and i still won
it failed racing a Ferrari F50, and i still won
07-07-2009, 05:02 AM
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Re: Can hot weather cause lower oil pressure even when oil temp is the same?
Thanks guys 
I'm not comparing apples to apples now anyway. The oil in the car when I hit the chunk of concrete and first noticed lower pressure was 11 month old Amsoil 5w40 (but only 2400 miles) w/ a K&N oil filter. I didn't feel like ordereing Amsoil and now that I'm not tracking the car I just threw in Mobil 1 5w30 w/ a Mobil 1 filter. I did this because I'd actually like for oil pressures to be a bit lower now that I don't have an oil cooler in the car anymore.
What I really needed to do was put fresh Amsoil 5w40 in the car and a K&N filter but oh well. At this point I'm just going to drive it and if it decides to blow up then so be it. I'm not going to pull the oil pan etc. Chasing something like this when it still makes perfectly good pressure is pointless. If the hot idle pressure drops more then I know something is going south. and it's not just the weather.
The other big variable is the fact that I put a stock hood back on which isn't vented and has a hood insulator whereas the DRM hood was vented w/ no insulator.
I'm not comparing apples to apples now anyway. The oil in the car when I hit the chunk of concrete and first noticed lower pressure was 11 month old Amsoil 5w40 (but only 2400 miles) w/ a K&N oil filter. I didn't feel like ordereing Amsoil and now that I'm not tracking the car I just threw in Mobil 1 5w30 w/ a Mobil 1 filter. I did this because I'd actually like for oil pressures to be a bit lower now that I don't have an oil cooler in the car anymore.
What I really needed to do was put fresh Amsoil 5w40 in the car and a K&N filter but oh well. At this point I'm just going to drive it and if it decides to blow up then so be it. I'm not going to pull the oil pan etc. Chasing something like this when it still makes perfectly good pressure is pointless. If the hot idle pressure drops more then I know something is going south. and it's not just the weather.
The other big variable is the fact that I put a stock hood back on which isn't vented and has a hood insulator whereas the DRM hood was vented w/ no insulator.
Last edited by Cobra4B; 07-07-2009 at 05:06 AM.
07-07-2009, 05:09 AM
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Re: Can hot weather cause lower oil pressure even when oil temp is the same?
Are you low oil pressure at warmup or at operational speeds? What is the exact pressure at warm idle?
Last edited by Newbsauce; 07-07-2009 at 05:13 AM.
07-07-2009, 05:32 AM
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Re: Can hot weather cause lower oil pressure even when oil temp is the same?
I don't have low pressure... just lower than I used to have. I have a high volume pump and with my oil cooler and 5w40 oil and a K&N filter I was seeing 47-49 psi at hot idle (about 205-210). Then after removing my oil cooler setup I was seeing 52-53 psi hot idle.
Then the other day I noticed it at 40-41.... after I hit a chunk of concrete on 264. The thing is I took out my oil cooler back in February and never really paid close attention until the other day.
Then the other day I noticed it at 40-41.... after I hit a chunk of concrete on 264. The thing is I took out my oil cooler back in February and never really paid close attention until the other day.