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Old 04-28-2012, 03:40 PM   #1
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Default Oil cooler in front of or behind radiator

Just something I've been thinking about lately... you usually see oil coolers mounted in front of the radiator, but is this really better than behind it?

assuming they are stacked directly on top of each other the pressure drop, and therefore the flow rate, through the two should be the same in either configuration. The only difference will be the air temp each one sees.

With the same flow rates, the temp differential should be the only variable which effects the heat exchanger's effectiveness.

Lets assume:
1. The heat exchanger increases the air temp by 20% of the temp differential (which seems pretty reasonable for these size/type from some quick research)
2. The air temp is 100* F
3. The water temp is 200*F
4. The oil temp is 250*F

With the oil cooler in front:
Oil temp differential: 250-100=150*
Rise in air temp: 150*.20=30*
Water temp differential: 200-130=70*

Combined differential (which should be an indicator of total system effectiveness): 150+70=220*

With radiator in front:
Water temp differential: 200-100=100*
Rise in air temp: 100*.20=20*
Oil temp differential: 250-120=130*

Combined differential: 130+100=230*

So with the oil cooler behind the radiator you should have more effective overall cooling system.

Of course, this is over simplifying things...as to actually calculate the heat transfer you have to solve a couple simultaneous equations with iteration, which I haven't done in years and am wayyy too lazy to try... but even so, both configurations should be pretty similar in terms of effectiveness, and the physical location of the oil cooler behind the radiator is definitely preferable (easier to install/repair/replace, less hose, easier to check for leaks)

What do you guys think? Am I missing something? I feel like there must be a good reason to mount the oil cooler in front, since most OEM's do it that way.

Here is a graph of heat transfer across a typical car radiator
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Old 04-28-2012, 06:09 PM   #2
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um...what makes you think air is going to go through the more restrictive oil cooler/radiator area than just through the radiator? You need ducting.

If you must, oil cooler in front of the rad assuming you have enough surface area to cool the water after accounting for the oil cooler. I still think you're going to struggle to make that oil cooler work. Even when I had it ducted under the car is was fail/aids.
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Old 04-29-2012, 01:58 AM   #3
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My question is, behind the radiator where? All that space on my vehicle is occupied by my bigass fan motors. Of course, real race cars have no fans, but I don't have one of those.

Second question is how do you get any airflow through it assuming you can mount it behind the radiator. Duct one of the fans to exhaust through it? This will decrease overall flow through the radiator and fan significantly.

I think if we were talking about a completely passive airflow scenario involving no fans, and if the oil cooler were the same dimensions as the radiator, then this could work. But my first impression is that mounting logistics and airflow realities get in the way of this being feasible on our vehicles.
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Old 04-29-2012, 02:32 AM   #4
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Along a similar line of thought, I've wondered about placing mine in front of the valve cover, so when the hood closes it's up against the extraction scoop.
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Old 04-29-2012, 09:12 AM   #5
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Hustler: Some air will still go through the more restrictive stack, just less... but that's not really important since either configuration could be ducted. After seeing the B&M cooler in person I see what you mean, no argument here

Mobius: This is the "Race Prep" forum I've got plenty of room behind my radiator... a lot more than in front of it!

Curly: That's not a bad idea at all.
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Old 04-29-2012, 05:45 PM   #6
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Handyman, you're ignoring flow. If you put the oil cooler behind the radiator, you are requiring the oil cooler to draw air only from air that has already passed through the radiator. The oil cooler would need to be ~2x as big as it otherwise would be to maintain the same temps.

If you put it in front of the radiator, the oil cooler gets some direct fresh air, and whatever doesn't go through the oil cooler is diverted to the radiator (either intentionally or by default, depending on your ducting).
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Old 04-29-2012, 09:16 PM   #7
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Quote:
Originally Posted by Handy Man View Post
Hustler: Some air will still go through the more restrictive stack, just less... but that's not really important since either configuration could be ducted. After seeing the B&M cooler in person I see what you mean, no argument here
I'm not always right, but when I am, um...lol.

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Originally Posted by Savington View Post
If you put it in front of the radiator, the oil cooler gets some direct fresh air, and whatever doesn't go through the oil cooler is diverted to the radiator (either intentionally or by default, depending on your ducting).
It's still an insanely gay set-up because you're limiting efficiency. I had this discussion with a retard a while ago who claimed "turbos are more efficient because they atomize air". Seriously.
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Old 04-30-2012, 03:33 AM   #8
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you have a modified front bumper so it depends, what size cooler did you get. my experience with this car is somewhat limited but ive done oil coolers on several cars. if you ran a nice duct from the bumper to your core i think you would be set. if you dont want to disrupt air flow or whatever mount a big core between the rad and IC. at some point volume be comes a burden on the oil pump but that is out my knowledge but I dont think you will have a issue.

if you have a big 8x11 or 11x11 size I think you will be fine with no special ducting. if you use a smaller core you will need air flow. I'm going to move my little 2x5x6 core to the passenger wheel area and then duct some clean air from the sides of the intercooler. Ive not done it yet but I think it will be ok the last event I was running a little hot with any ducting, core mounted behind the latch for the hood, so like zero air.
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Old 04-30-2012, 12:16 PM   #9
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Quote:
Originally Posted by Savington View Post
Handyman, you're ignoring flow. If you put the oil cooler behind the radiator, you are requiring the oil cooler to draw air only from air that has already passed through the radiator. The oil cooler would need to be ~2x as big as it otherwise would be to maintain the same temps.

If you put it in front of the radiator, the oil cooler gets some direct fresh air, and whatever doesn't go through the oil cooler is diverted to the radiator (either intentionally or by default, depending on your ducting).
Have you tried it? I guess what I'm trying to get at with all of that is that with the oil cooler behind the radiator, the oil cooler wont work quite as well, but the overall cooling system should be more efficient.


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Originally Posted by hustler View Post
It's still an insanely gay set-up because you're limiting efficiency.
It depends on your perspective. If you don't care about aero, and don't mind having a bunch of air inlets to feed various coolers; yes, each cooler will be most efficient with its own ducted flow

HOWEVER, if you do care about aero, it's much more efficient to use less air inlets (more specifically, having air inlets with less total frontal area). To achieve the same amount of cooling with less air inlet frontal area, you will have to use less airflow, but transfer more heat to it. This can be accomplished by using larger/thicker heat exchangers, and/or stacking them.
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Old 04-30-2012, 01:35 PM   #10
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Here's where I put mine:


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Old 04-30-2012, 02:07 PM   #11
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Quote:
Originally Posted by gtred View Post
Here's where I put mine:


Cool!
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Old 04-30-2012, 02:07 PM   #12
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My oil cooler is below the radiator and at an angle. All the air coming in through the front opening is ducted and goes just through the radiator. Ducts from openings in the front lip spoiler feed air to the oil cooler separately. Seems to work pretty darn good.

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Old 04-30-2012, 09:44 PM   #13
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looks pretty nice, how are the temps? do you run a under tray? IF you built a box attached to the core and the housing it would be likely be even better


Hustler what core is that? I was looking at a fluidyne unit but I'm not going to drop that coin right now. how do you have the lines routed? i;m surprised you have clearance for the fitting with the port location on that core.

the air flow I plan to use with be the open space next to the inter cooler. the problem is that my car does not have fog holes so I either need to find a set of the oem fog surrounds before they became part of the bumper (99 i think?) when I set up my brake vents.

I'm going to seal off the sides of the bumper to force air through the IC and mount a napa duct and either make a custom duct to the core or just buy one. I'll post pictures this week, have a 3 day event this weekend so I need to do something. I might just say screw it and order a b&M core for 70 bucks and be done. cheap and I pretty sure that will take care of the temps.
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Old 04-30-2012, 10:09 PM   #14
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Don't worry, Hustler will proceed to remind you repetitively how bad of a choice the B&M is

Have you considered the used ebay Setrab's that are like $90? I'm considering returning my B&M and ordering one of them... but plenty of the guys I race with have had good luck with the B&M despite its inferior design.
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Old 05-01-2012, 01:22 AM   #15
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well yes I have, I'm not sure it is worth saving 100 bucks to use a oil cooler that may have been on a blown motor is worth it.

what happened? did he get a leak or something? he is generally very opinionated which is fine but Ive used them and if you go a little big they are fine. they have the same design as other manufacture. I know they are not efficient as the better cores, setrab, mocal, fluidyne, but they cost 1/3 the price. I also see to recall a thread where he used 8an lines and if he had a pressure issue it may have been the lines. I'm open to hear what he says but I know from prior experience they are ok, Ive used on on another car, it was also a 1.8,a audi 20v big turbo and the core worked awesome for many years on track. I had no ducting, just mounted it in place of the stock intercooler and all was well.

I was also thinking about buying a oem model from another car, I was checking out one from a jag and one from a bmw, oem new. not a bad route but then I gotta adapt whatever they are BSN to AN fittings so that will add 20 bucks.
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Old 05-01-2012, 12:07 PM   #16
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Quote:
Originally Posted by psreynol View Post
looks pretty nice, how are the temps? do you run a under tray? IF you built a box attached to the core and the housing it would be likely be even better
Plywood splitter extends forward of the lip ~4 to 8" depending on which one I put on and extends back to about 6” in front of the steering rack so I don't run a factory undertray. I had thought about building a duct plenum to force all the air from the hoses through the oil cooler but it really is no worse now than sticking the cooler in front of the radiator not all the air is going through it there ether.

I don’t have good oil temp data but I will say overall engine temps are reliably steady for a 30 minute session or more with the car making ~350 RWHP and running laps 5 to 10 seconds under spec Miata lap records.

Bob
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Old 05-01-2012, 05:34 PM   #17
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psreynol; I couldn't agree more, glad to see I'm not the only one who thinks used coolers aren't the best idea.

One warning about the B&M: I know a guy who cracked the inlet on his because the hose was pulling on it, luckily he caught it early, but if it had failed suddenly on track, it could have been the end of his motor. He still trusts them enough to use them again, just make sure your hose routing doesn't put stress on the cooler's inlet/outlet. (to be honest, I bet this could happen to any AL cooler. Metal fatigue is a bitch)
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Old 05-02-2012, 01:49 AM   #18
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Quote:
Originally Posted by Handy Man View Post
psreynol; I couldn't agree more, glad to see I'm not the only one who thinks used coolers aren't the best idea.

One warning about the B&M: I know a guy who cracked the inlet on his because the hose was pulling on it, luckily he caught it early, but if it had failed suddenly on track, it could have been the end of his motor. He still trusts them enough to use them again, just make sure your hose routing doesn't put stress on the cooler's inlet/outlet. (to be honest, I bet this could happen to any AL cooler. Metal fatigue is a bitch)
that will happen to any core, it will happen to fittings, and you can "pre fatigue" them by not holding on to the core fitting when you tighten them... or so they say.

I had a setrab core on a car and all the paint fell off after a being on a car for one winter in Chicago. that is pretty shitty. I know they make a good core but that is lame, and reminds of other companies that say " oh its a racing part when you question durability yet they brag it is 'track proven and tested for the street ( stoptech).

I wanna try a fluidyne core. might buy one of those use and see if i can have it "professionally" cleaned or something
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Old 05-02-2012, 04:21 PM   #19
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How about internal oil cooler in the radiator? Ron Davis makes em.
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Old 05-02-2012, 06:02 PM   #20
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Quote:
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How about internal oil cooler in the radiator? Ron Davis makes em.
This is exactly what I've been looking for. Do you have a link?
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