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  #1 (permalink)  
Old 08-08-2008, 04:47 AM
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Cobra Make, Engine: Homebush, Dodge Viper blue, white stripes, black traditional interior 347, AFR heads, Morrison injection, motec, T5, live axle, lead car Bathurst drivers parade 1999, 5.0L Cobra Nationals sprint title 2001
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Default Less oil Pressure

Boys

Snaken is back running, no more oil leaks from the custom individual throttle body intake manifold.
BUT you have to make changes, so I fitted an oil cooler
The out come ............... suddenly I have less oil pressure. WHY would that be.
I am running from block through filter down to cooler and back to the engine. Running same oil, gauge is manual ( Smiths) but gone from 50 ish to 40 ish ???
Got 30 lbs on crank but only 40 ish on 1500 rpm. Only just got it fired up still on axle stands will give it a rev up in the morning, but anyone got ant ideas
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Old 08-08-2008, 05:41 AM
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I lost about 8 psi of oil pressure when I added an oil cooler to my road racer, small block Ford engine... I have used 4 different oil coolers over the years (headered type and single pass type) and get about the same results with all four... also using 12 AN lines... Talking to others about this, I think a 5 to 10 psi loss with an external oil cooler seems about the norm...........

David
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Old 08-08-2008, 05:52 AM
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David,

What pressure did you drop to, and what is a normal oil pressure with oil cooler ?????
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Old 08-08-2008, 06:08 AM
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I have a Melling HP series oil pump that is adustable for pressure... Normally I run about 50 to 55 psi on track at speed once the oil is at temp (220 to 240 degrees)....idle oil pressure is 30 to 35 psi at temp...
I really like this oil pump, it is a blue printed pump from Melling is under 50 bucks.... it is stock pressure and stock volume (I don't care for high volume pumps), but where the spring is, instead of a plug in the hole, it has a large Allen head screw, screwing it in or out will adjust the pressure......

Start-up, cold oil, it goes to 60 to 65 psi, as the oil warms up, pressure drops....I'm runnig Mobil I 15/50...... I have tried other oils and get within 5 psi regardles of what type/weight oil I use....

Motor is a 331 cu in stoker, 12.75 to 1 compression, turning from 3000 to 7000 rpms on track......

For a street car/motor, I would think anything over 40 psi at speed would be fine, and 25 to 30 psi at idle.....
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Old 08-08-2008, 06:08 AM
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I also dropped 9 psi hooking up the cooler. This was with the oil cold. Once it warmed up and the oil thinned the oil pressure actually went up and almost matched hot oil pressure with no cooler Don't worry about it and don't beat on it until it's fully warmed up.


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Old 08-09-2008, 05:06 PM
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Default Thanks

Thanks guys, took it out for a spin yesterday in the Melbourne sun.
Runs at 45 lb with engine warm. Will leave the cooler on and test at the Nationals in October.
Thanks for your help.
Snaken
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Old 08-09-2008, 06:49 PM
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I have a 351W with oil cooler, high volume oil pump, -10 lines and a thermostatic sandwich adapter. Using 10-40 oil I run 55 lbs pressure until the thermostat on the oil cooler opens, then the pressure drops to 50 lbs. Believe it or not, I have found some pressure differences depending on which oil filter I use. Remember also that oil viscosity can also affect oil pressure. In my opinion, 45 lbs in a warm engine ain't bad so I would leave well enough alone. If you are not running a thermostat, please do yourself a favor and install one.
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Old 08-09-2008, 07:16 PM
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Remember flow pressure drops around 5 psi for each right angle turn, your cooler adapter between block & filter more than likely has a couple of drillings that nearly equate to this. The reason the pressure seems to increase when hot in this situation is the oil has thinned and has less resistance to flow. The advice not to rev it when cold is VERY GOOD and will save you $$$$ long term.
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Old 08-09-2008, 07:34 PM
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My oil pressure sensor is at the end of all the plumbing, after the filter and after the cooler. By going from 20W-50 to synthetic 5W-30 my oil pressure increased. I imagine the thinner oil can navigate the system far more easily and so loose less pressure along the way. I would have to think that less oil (if any) is now being sent through the bypass valve.

Bob
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Old 08-11-2008, 06:21 AM
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Thanks Guys,

I will check out the thermostat. May even try thinner oil at the next change. For now I will drive with one eye on the speedo as I am running out of points and the other on the oul pressure guage.

Snaken
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