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Dual oil coolers: Variable line diameters?

Old 08-23-17, 11:13 AM
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Dual oil coolers: Variable line diameters?

I have decided to run dual OEM style 1st/2nd gen oil coolers in my 13b 1st gen endurance racer.

I want to run them in parallel as this seems to me the best setup.

I have decided to use AN fitting to get the job done and so started shopping around for fittings.

My original thought was just to use 10-AN fitting/tubing all around since that seems standard but when I went to look for Y-splitters it seems most are 10-AN to two 8-AN. (Yes I did find a 10-10-10 but it's a 90 degree T splitter and that seems restrictive to me)

It occurred to me that going 10an from the front cover into two 8an fittings into the coolers and then back to 10an to the block would help minimize pressure drop when splitting to two coolers so my question is this:

Does anyone run 2 oil line diameters in their dual cooler setups? Would this be specifically ill-advised?

Or, like most things, is this just massively overthinking the whole thing and that either way would achieve the goal of keeping temps down on long stints?

Thanks!
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Old 08-24-17, 09:32 AM
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I figured I might be overthinking it. Will run whole system with 10AN
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Old 08-24-17, 10:33 AM
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As far as I know most people just use a t-fitting for simplicity and to keep the lines as short as possible. I'm not aware of anyone having problems with this type of setup except on street cars that have trouble getting ENOUGH oil temp in the system. Do you also have proper ducting surrounding the coolers and radiator? I feel this is a much bigger factor to whether the system will cool efficiently or not than using t-fittings vs y-fittings. You could also delete the thermostats in each cooler and go to a high flow t-stat like the improved racing unit if you are concerned about increasing the overall system restriction
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Old 08-24-17, 12:21 PM
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Originally Posted by Lavitzlegend View Post
As far as I know most people just use a t-fitting for simplicity and to keep the lines as short as possible. I'm not aware of anyone having problems with this type of setup except on street cars that have trouble getting ENOUGH oil temp in the system. Do you also have proper ducting surrounding the coolers and radiator? I feel this is a much bigger factor to whether the system will cool efficiently or not than using t-fittings vs y-fittings. You could also delete the thermostats in each cooler and go to a high flow t-stat like the improved racing unit if you are concerned about increasing the overall system restriction
Thanks for the input. So I am doing everything at once, that is, building an air dam, installing dual coolers, and making proper ducting for the whole system.

Can't keep wasting track weekends with an overheating car.
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Old 08-24-17, 01:20 PM
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Yeah. I'm going to revise my ducting to allow both oil coolers and fittings and lines to fit inside the ducting with just a hole for the feed and return oil lines to poke through and will hopefully be done with cooling concerns as well. My first iteration was the same width as the radiator core and that meant I had to cut holes in the sides of the duct where the stock oil cooler mounts because they are just barely too wide to fit like that. V2 should be pretty solid though
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Old 08-25-17, 12:16 AM
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If you ran in series it wouldn't matter, but if you run two coolers with different levels of resistance in parallel, wouldn't all of the oil only go through the one with less resistance?
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Old 08-28-17, 10:21 AM
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It's actually the opposite. The oil molecules in a parallel setup only have to go through 1 cooler so the pressure would be the similar to stock and the pressure would be a self regulating system. If there is a pressure rise for 1 cooler, molecules would flow to the other to a point where the pressure in that section rises causing molecules to be diverted to the first cooler, etc etc. There is slightly more line the molecules going to the furthest cooler have to pass through which would create slightly more restriction but not enough to be noticeable.

In a series setup you get worse delta T in the second cooler and you force all the oil through 2 coolers which increases your system resistance leading to pressure drop on the "cold" side going into the engine.

Again, I think proper ducting is the most important piece but if you are set on going to a 2 cooler setup I don't see why you wouldn't plumb them in parallel.
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Old 08-28-17, 11:56 AM
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I used -10 hose and tee fittings at the inlet/outlet of the first oil cooler that allowed me to run a second oil cooler in parallel. Below is my quick sketch. Even though the flow might take a small hit with tee fittings over "y" fittings, the overall number of joints/connections/fittings/hoses was a bit lower using tee fittings. I viewed this as an advantage; the less AN hose ends I had to assemble together, statistically the lower the risk of a failure.

I kept the thermostats in both oil coolers and have done temperature measurements that proved that oil flowed pretty much equally to both coolers.

Just for reference, the advice on ducting is also key. For my streetport NA 13B, I had the following for 85-90f ambients at 6,000' elevation, primarily 2nd and 3rd gear speeds:

Single oil cooler, stock location: 280f+ (yikes)

Dual oil coolers, simple flat aluminum under tray sheet: 230f

Dual oil coolers, complex aluminum ducting: 200f, max 210f drafting


Last edited by Andrew-s; 08-28-17 at 12:04 PM.
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Old 08-28-17, 01:33 PM
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Originally Posted by Andrew-s View Post
I used -10 hose and tee fittings at the inlet/outlet of the first oil cooler that allowed me to run a second oil cooler in parallel. Below is my quick sketch. Even though the flow might take a small hit with tee fittings over "y" fittings, the overall number of joints/connections/fittings/hoses was a bit lower using tee fittings. I viewed this as an advantage; the less AN hose ends I had to assemble together, statistically the lower the risk of a failure.

I kept the thermostats in both oil coolers and have done temperature measurements that proved that oil flowed pretty much equally to both coolers.

Just for reference, the advice on ducting is also key. For my streetport NA 13B, I had the following for 85-90f ambients at 6,000' elevation, primarily 2nd and 3rd gear speeds:

Single oil cooler, stock location: 280f+ (yikes)

Dual oil coolers, simple flat aluminum under tray sheet: 230f

Dual oil coolers, complex aluminum ducting: 200f, max 210f drafting

Awesome thanks! I see you put the T fitting directly in the coolers. Not sure why I didn't think of that, but I think that's the best solution.

I was for sure overthinking things with my -8 / -10 combo lines. I'l def doing just-10

Also, I buy fully into the church of radiator ducting and will most assuredly be making some crazy duct work to properly channel air to both coolers and radiator.
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Old 09-03-17, 12:53 PM
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Originally Posted by Valkyrie View Post
If you ran in series it wouldn't matter, but if you run two coolers with different levels of resistance in parallel, wouldn't all of the oil only go through the one with less resistance?

This is why I was steered away from a parallel setup. The hotter cooler has thinner oil in it, so it flows more, so more oil flows through the hotter cooler, and the cooler cooler ends up being stagnant.

Might work okay if you kept the thermostats, though.

I'm a little surprised that you can't find 10-10-10 Ys. I know they exist, just this week I worked on a low mount turbo oil scavenge system that uses a 2-stage pump and a 10-10-10 in the return to the oil pan.

Whole bunch of them at Summit

What is interesting is the system I worked on didn't have direct male fittings, it was just a block with AN female threads, so you needed an O-ring seal type fitting to adapt to male. So it was much heavier and bulkier.

Last edited by peejay; 09-03-17 at 12:55 PM.
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Old 09-05-17, 01:40 PM
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Originally Posted by peejay View Post
This is why I was steered away from a parallel setup. The hotter cooler has thinner oil in it, so it flows more, so more oil flows through the hotter cooler, and the cooler cooler ends up being stagnant.

Might work okay if you kept the thermostats, though.

I'm a little surprised that you can't find 10-10-10 Ys. I know they exist, just this week I worked on a low mount turbo oil scavenge system that uses a 2-stage pump and a 10-10-10 in the return to the oil pan.

Whole bunch of them at Summit
So I was searching on Amazon, since I have some gift cards, but yes, I then went to summit and the Y splitters are readily available.

Very interesting point on the heat and viscosity. Because while I wouldn't expect much flow difference between two identical coolers it would make sense that the thinner-hotter oil would more easily flow through the cooler, thus putting more oil through the cooler that is working the hardest.

That said, I suppose you could make the argument that the slower moving-thicker-cooler oil would then just meet up with the hotter oil and equalize temps a bit as it flows into the motor.

Again, I just think perhaps it's all a bit of overthinking. With two coolers plumbed in, with proper ducting to both, I think temps will come way down into the manageable range.
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Old 09-05-17, 07:45 PM
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Yes, certainly it will function at least like a single double-height cooler, in that every header-tank radiator will have hotter and cooler areas. But as long as you get the additional area with "height" instead of "length" or "depth" then it will definitely be beneficial.
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Old 09-15-17, 03:03 AM
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I'll be running two of these. One with a temperature sensor, the other with a pressure sensor. Should help me get an idea of what's going on in the system as a whole.

https://www.summitracing.com/parts/m...6120/overview/
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Old 09-18-17, 08:14 AM
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Originally Posted by SirLaughsALot View Post
I'll be running two of these. One with a temperature sensor, the other with a pressure sensor. Should help me get an idea of what's going on in the system as a whole.

https://www.summitracing.com/parts/m...6120/overview/
Yeah, I was actually thinking there must be splitters with sensor ports as well, although those are freakin $$$$$$

Let me ask you this though: I assume you would want to take temp post cooler, which leaves you the pre-cooler splitter to take pressure. This shouldn't matter though right? As pressure should equalize through the entire system?
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Old 09-18-17, 09:07 PM
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No the pressure will be different (lower) after passing through the coolers. fluids always flow from high pressure to low pressure. If it were me I would want to know the temperature pre and post cooler and not really care about the pressure because you have a pressure regulator as it enters the rear of the engine anyway. The oil post oil pump should be the hottest it is through the whole system which is why Racing Beat recommends not going over like 210 at the oil pedestal which is post cooler. Pre cooler will be decently hotter than this
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Old 09-26-17, 01:06 PM
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Originally Posted by Lavitzlegend View Post
No the pressure will be different (lower) after passing through the coolers. fluids always flow from high pressure to low pressure. If it were me I would want to know the temperature pre and post cooler and not really care about the pressure because you have a pressure regulator as it enters the rear of the engine anyway. The oil post oil pump should be the hottest it is through the whole system which is why Racing Beat recommends not going over like 210 at the oil pedestal which is post cooler. Pre cooler will be decently hotter than this

This man speaks the truth (with regards to temps as well as the parallel vs series question). We have a target of ~240 degrees pre cooler on our RX3 and GT cars and always run parallel coolers if allowed/legal.
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Old 09-26-17, 07:12 PM
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Originally Posted by dguy View Post
This man speaks the truth (with regards to temps as well as the parallel vs series question). We have a target of ~240 degrees pre cooler on our RX3 and GT cars and always run parallel coolers if allowed/legal.
Do you/have you ran a sensor post cooler? If so, have you checked the ΔTpre/postfor the different setups (series/parallel)? It seems worth checking out.

Based on the graph below (10W-40), the viscosity of oil seems negligible from 70-100C. This makes me curious about the flow in a parallel setup.


Source: Engine oil ? viscosity table and viscosity chart
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Old 11-05-17, 04:24 AM
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In my experience, two stock FC coolers whether in series or parallel will easily do the job given enough airflow. Getting fresh air to the coolers is sufficient to eliminate all math and engineering in this thread.The two added vents in the front bumper and a deflector that sends that air over rather than through the radiator dropped oil temps from about 240* down to 200*. That's at ~480whp 20 minute stints The coolers are in series.
Attached Thumbnails Dual oil coolers: Variable line diameters?-racerx72.jpg   Dual oil coolers: Variable line diameters?-img_6025.jpg  

Last edited by Carl Byck; 11-05-17 at 04:31 AM.
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