# Oil Cooler line size ???



## Seax_Smith (Jun 1, 2007)

Looking to install an aux oil cooler onto my ABA digi hybrid. Recently did a racco rad instal and pushed the rad to the far left which left me a fair amount of space on the right side behind the grille. 

Will be filling that space with an oil cooler - a tall, not so wide one as deep as I can find. Want to keep the lines as short as possible and the over all path of the oil as close to the 'elevation' of the oil filter flange. 

Questions I have are: 

What is the best diameter line to run with it to minimize the loose of pressure and volume? 

Would I be better off running the lines off the top of the cooler or running flow in on the side top and picking up the return off the side bottom? 

Thanks much.


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## ps2375 (Aug 13, 2003)

1/2" line should be fine. And mount it however you want and as close or as far from the motor, with that size line (or bigger) you will be just fine. The "euro" style cooler has both lines on the bottom, I had them both on the top when I had the sandwich plate and radiator type cooler, it seems not to matter much, as the air will get pushed out however it is mounted.


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## Seax_Smith (Jun 1, 2007)

-8AN huh? 

Seems what most of what I am finding is set up for too. 

I think too much sometimes, and really enjoyed minima/maxima problems in calc. 

Thinking the shorter the runs to and from the sandwich plate the the less the elevation change, the less pressure & flow I will loose. Trying to avoid tight 90* bends is proving to be a bit of a pita too. The 90* sweeps I have found have rather restricted ID's too. Found some banjo bolt style AN fittings, but they have a height requirement issue and their own flow issues.


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## ps2375 (Aug 13, 2003)

45* turns and the hose should be just fine.


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## nairmac (Jan 22, 2004)

I run -10an lines to a Volvo 740 turbo oil cooler, each line has a 90* near the cooler and a 45* at the sandwich plate. I never have exceeded 100*C in hard or stop and go driving in Vegas on 110*F+ days.


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## Seax_Smith (Jun 1, 2007)

What engine and oil pump?

What's the pressure at the head look like?


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## nairmac (Jan 22, 2004)

Seax_Smith said:


> What engine and oil pump?
> 
> What's the pressure at the head look like?


It's an Audi 3A block, ABA oil pump, digi hydro 8V head with work done. Pressure at the head i'm not sure, have only gone by the interior gauge and verified with a second gauge. 5+ bar cold, 2.5 at the lowest when hot, but usually right about 3. I run 15w 50 synthetic oil currently.


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## Seax_Smith (Jun 1, 2007)

nairmac said:


> It's an Audi 3A block, ABA oil pump, digi hydro 8V head with work done. Pressure at the head i'm not sure, have only gone by the interior gauge and verified with a second gauge. 5+ bar cold, 2.5 at the lowest when hot, but usually right about 3. I run 15w 50 synthetic oil currently.


Thanks. 

The stock Audi 5 bar is pressure at the head.
5 bar = 72.50 PSI
2.5 bar = 36.25 PSI

Pressure at the flange tops out about 10 bar a/o 150 PSI

Funny thing is I know it isn't going to matter in day to day driving, but I still want to maximize cooling and at the same time minimize the decrease in pressure and volume of the oil flow. I'm sure adding the extra distance that an oil cooler will add plus the added restrictions in the lines, that there will be a flow loss and a pressure drop. Then there is that whole pressure volume interaction.

Wish I didn't have to figure out stuff like this. Am sure -8AN to -12 AN will both cool my lubricate Digi/OBD1ABA more than sufficiently, but I need to know (a good approximation of) the optimum option to stop thinking about it.


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## ps2375 (Aug 13, 2003)

Oil is not a compressible fluid, so those issues will be a minimal factor. I have run coolers in the past with as much as 4-5 feet of total hose length with no notice-able pressure drops at the head.


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## Seax_Smith (Jun 1, 2007)

I know. I am worried about a theoretical (minimal) loss in pressure and flow rate. Until I work it out, I won't do anything - then I'll install whatever I find (i.e. RP&P the first Volvo turbo I find).

Sad thing is I won't be satisfied until I do volume and pressure tests at different diameters and lengths - which isn't going to be happening. Sometimes, I really hate what one of my calc. profs instilled in me.


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## ps2375 (Aug 13, 2003)

You are way over-thinking this. I have the Volvo set-up on the mkIII Golf, and those hard lines might be 1/2" on the outside and that car has never had any issues with oil pressure since it was installed in the car.


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## nairmac (Jan 22, 2004)

ps2375 said:


> You are way over-thinking this. I have the Volvo set-up on the mkIII Golf, and those hard lines might be 1/2" on the outside and that car has never had any issues with oil pressure since it was installed in the car.


Agreed. Oil temps and oil weight will have more to do with the flow than anything else.


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## Seax_Smith (Jun 1, 2007)

Have admitted I am over thinking it. Until I have an understanding of how the variables interact with each other, I wont do anything. I already know that I am talking about handful of PSI and or a degree or two. In essence it all comes down to work load on the pump anyhow. Outside of the high volume pump I am already running, there isn't much to be change there. 

[You are talking to someone who spent a couple of extra hours and a whole lot of extra bullet connectors and heat shrink installing Euro tails so I can do a plug-n-play swap back to US spec lighting. Will I ever use this? probably not.]


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## ps2375 (Aug 13, 2003)

Unless you mount/install pressure senders and temp senders and even flow meters through out the system on a running motor in a car identical to yours, you will never know how all these variables will interact.

OCD is one thing, but you are getting kind of ridiculous, you may have a few #'s in press drop, but the added viscosity of the cooler oil will more than cover that.

And the pump really won't be working any harder than normal, cause the only time a pump works hard is when the oil is cold and the pressures are at their max to the point the internal relief lifts. Just before that point is max load on the pump.


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## Seax_Smith (Jun 1, 2007)

You don't get it. It isn't about .01 PSI and 3 drops/minute at the head. It's about the problem itself. It's a system with three variable: flow rate vs temp vs pressure. It can be optimized or minimized.

http://www.youtube.com/watch?v=FrFlkNHwIVM

Practical solution is easy: Availability of oil cooler ID is the limiting constraint. Someone has already done the measuring and the math. (Gotta love capitalism for making things better.) Second constraint is the farther you move something the more energy it takes. ....

End result: Install the oil cooler with the biggest / most efficient surface area possible. Be sure the ID of the sandwich plate and the oil cooler are the same and match that ID with the connecting lines. Make the lines as short as possible and keep the intake and output of the cooler the same height as the connectors of the sandwich plate. The larger greater the variation in cooler ID vs the line ID will determine if cooling and flow rate will be maximize or if pressure will be maximized. ...

Does any of this matter for an 8-valve that doesn't have an oil temp issue? No. Do I want to have understand what I am doing and why I am doing it? Yes.


[Won't tell you about how long I spent optimizing a 32 quart filter for a 125 gallon aquarium: turn radi vs diameter. Will tell you that after a year of running it was maybe 40% 'dirty']


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## ps2375 (Aug 13, 2003)

There isn't going to be much variance in thermo sandwich plates, and depending upon conditions, that will be sending a varying amount of oil to the cooler, so all the things you are worried about go out the window. And I think, but not 100% on this, most oil coolers have the same size inlets and outlets on them, not much to "tweak" there. And your motor will not be at a constant rpm the whole time it is running either, unless you have a CVT tranny, which I doubt.Again, all those calculations are null and void, well except at that one optimum pressure and flow rate that corresponds to that one optimum rpm.


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