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Jonny Hart

Rear Mounted Oil Cooler project.

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Hi All,

Having weighed up the pros and cons of a rear mounted oil cooler with thermostatic fan I’ve decided to move ahead with this project.  
 

The goal is to delete all of the factory oil lines and thermostat for a simplified and cleaner looking installation.    
 

There should also be a fairly good weight saving and cost savings too when compared to the price of original parts. 
 

At the moment, the way I have configured the new oil lines is for cars with SSI/early style exhausts layout. 

Having spend considerable cash on OEM oil lines around 7 years ago, I was quite surprised to find them in quite grotty condition and very difficult to undo as if they’d been on there for 30 years. 

I’ve always thought this peculiar arrangement of bends and rubber pipe to the opposite of ‘form follows function’

So here is the starting point:

802024C4-D38F-4343-821F-BA3BD7E5A821.thumb.jpeg.d044bb5194750d37c735d609e0e974c7.jpeg

TBC...

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Looking at the aftermarket, the biggest 3.2 style under wing oil cooler is a 44 row unit that is 110 x 344 mm giving a surface area of 40,000 mm2.   This is considered a BIG oil cooler suitable for a 3.6.   Because of space constraints it is limited to running a 5 inch fan in a blowing configuration.  The fan covers less than half the cooler.  
 

The rear fender quarter (opposite side to oil tank) allows fitment of an oil cooler that is 62,000 mm2.    The square form factor allows fitting of an 8 inch fan with full coverage of the entire cooler.   It will be a sucker fan which offers greater flow than a blower. 
 

These numbers give me confidence that my 100% fan assisted cooler will be able to perform at least as well if not better than the largest aftermarket cooler which gets a little ram air from the front (supposedly).  

TBC...
 


 

 

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Posted (edited)

Oil cooler in place (fan not fitted)

A53247CD-FB35-47CD-940B-E9B9AFD9AFAA.thumb.jpeg.4bece55c775daeee7470010394d400d7.jpeg

Pipework will be 3/4 inch ID hose which when mated to a fitting gives a bore size of 15.5mm.    Now of course Porsche use 22 mm pipe and most of the fittings have a bore of around 17.5mm.   I stewed on this for a few days, reading about the importance of ‘wide bore’ oil coolers etc.   Maybe I need to go to 1 inch pipe?  Expensive and hard to find.    Then a lightbulb moment, isn’t the case scavenger pump fitting M22?  How could they thread that and maintain 17.5mm bore?   Only one way to find out!

857530A9-831E-425A-BC5C-5ABF18143394.jpeg.3e71e317f02d7881cee0aff07853ec3d.jpeg

Guess what?  15.5mm ID on the crankcase fitting!  

I am using lightweight alloy -12 fittings with a push fit hose.  Yes, push fit with no tools required. The hose has a special diagonal weave that tightens the hose to the fitting under pressure.  Good for 250 PSI so no issues there.
 

TBC...

 

Edited by Jonny Hart
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I'm not understanding/convinced of the need of a rear mtg oil cooler so following your progress with interest 🤔

Watch out for electric fan CFM no's as most are only relevant for a perfectly sealed, fully enclosed duct installation and have no built in contingency for any for any leaks in the installation. The numbers quickly drop off a cliff when leaks are factored in.

Jonny, do you plan to market a kit when your done or a personal project to tidy up your car?

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Posted (edited)

So I swapped that out for a -12 fitting.  Same ID.  

699C59B3-4E8E-45F1-AB19-39F3884BD2A3.jpeg.7ab70b3ed2270520bee5dd322a96d1a3.jpeg

(Can only get these in blue.  Not my thing but it will be hidden)

So I set about routing the pipes and find a place for the oil thermostat.   If you are familiar with the SSI setup you will know the J (or ?) pipe that goes under the gearbox.  This routing is ideal to get across from the oil tank.  After a clean up, this is what my arch looks like, tidy!

A7457D03-4650-4AFC-8809-37741A40CB33.jpeg.4d5f06ff0459ed616d65401ad6bc2b30.jpeg

On the other side, the new scavenge pipe meets with the cross pipe and joins at the new thermostat:

13E1FAA1-F8E2-41CD-961F-406C40E630C6.jpeg.36160fa1515eca6534ca96c5ac691b3d.jpeg

Where the pipe is close to exhaust I’m using a temp shield sleeve.  Probably overkill as it’s only on the heat exchanger, not the manifold itself.

TBC...

 

 

 

Edited by Jonny Hart

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Posted (edited)
9 minutes ago, World Citizen said:

I'm not understanding/convinced of the need of a rear mtg oil cooler so following your progress with interest 🤔

Watch out for electric fan CFM no's as most are only relevant for a perfectly sealed, fully enclosed duct installation and have no built in contingency for any for any leaks in the installation. The numbers quickly drop off a cliff when leaks are factored in.

Jonny, do you plan to market a kit when your done or a personal project to tidy up your car?

Yep,   I know a bit about fan sealing from AC... and static pressure - that’ll do your head in. 
 

You do know IB is the birthplace of our kits, right? 👍

 

Edited by Jonny Hart

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27C7D272-014E-4512-BBF3-81C25E12BC53.jpeg.07c9f9722a45b36b2e0d076a4e041a76.jpeg

So that’s where we leave it, pending a couple of adjustments on fittings - need slightly different angles on the cooler. 
 

Fan mock up.  Will be designing a sealed shroud for this.  Not the actual fan we will use in the photo either...

C5DDDB4D-C740-4157-8371-F56DB2F0F03C.jpeg.889e10835d856f41492fc78032b02eee.jpeg

 

15 minutes ago, World Citizen said:

I'm not understanding/convinced of the need of a rear mtg oil cooler so following your progress with interest 🤔


If you been to the ‘crushed oil line / I broke my thermostat / want SSIs’ triangle you would understand .

 

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Posted (edited)

...or an early car without an oil cooler. 

Edited by Jonny Hart

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5 minutes ago, Jonny Hart said:

27C7D272-014E-4512-BBF3-81C25E12BC53.jpeg.07c9f9722a45b36b2e0d076a4e041a76.jpeg

So that’s where we leave it, pending a couple of adjustments on fittings - need slightly different angles on the cooler. 
 

Fan mock up.  Will be designing a sealed shroud for this.  Not the actual fan we will use in the photo either...

C5DDDB4D-C740-4157-8371-F56DB2F0F03C.jpeg.889e10835d856f41492fc78032b02eee.jpeg

 


If you been to the ‘crushed oil line / I broke my thermostat / want SSIs’ triangle you would understand .

 

Only had one out of the 3, wasn't really a biggie

I do however have a basic understanding of design/engineering of cooling systems on performance cars and also witnessed 1st hand how difficult it was to out 911 Porsche on the Singer DLS project when it comes to engine/oil cooling which is why I'm following with interest.

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^ We will see and of course every system has its limits.   It might not be suitable for all cars or super hot climates but that’s more the reason for having a go.  
 

On my SC, it had the tube type cooler with no fan and no slit in the bumper.  
 

i have a limited understanding of aero but I’ve been reading a lot about air flow in wheelhouses and as far as I can make out, there’s just a riot of turbulent air In a wheel house, not so much a flow.   The front wheel will have a high pressure area in front of it, right below the standard oil cooler.  This could be a potential barrier to  hot air escaping below. 

With the 911 engine, the air is pushed through  the fins to the underneath of the car by the engjne cooling fan.  The low pressure area below the engine will also suck the air through and aid the fan. Since my fan will be in the same area I expect a similar effect.  

Thoughts / experience welcome.  

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From ‘build your own race car’

Another useful technique is to use the natural high and low pressure areas created by the bodywork to perform functions. For instance, Mercedes, back in the 1950s placed radiator outlets in the low pressure zone behind the driver. The air inlet pressure which fed the radiator became less critical, as the low pressure outlet area literally sucked air through the radiator.’

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Posted (edited)

^^^ not relevant when stuck in traffic

My concerns are free flow motorway driving will create very different cooling challenges compared to stuck in traffic driving, 2 very different conditions for a radiator/cooling system to cope with

From 'been there, done that, seen that on a race car but I know enough to know I don't know enough'.... 😅

'Call me if you want to chat!' 

Edited by World Citizen

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^. But my SC has no fan at the moment.    
 

Re stuck in traffic.   Are you seriously suggesting that an SC tube rad with no fan is better than a bigger modern oil cooler with a fan?   🤷‍♂️ 

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Trying to work out what the raison d’etre is for this experiment/modification. Are you looking to improve cooling? What for? Cooling on air cooled cars is pretty good. Are you looking to simplify? What for, the existing system is plumbing. To negate need to replace crushed pipes? Thought they were available from ECP. Thermostat? That’s not big bucks in the scheme of things is it. I’m guessing you need room up front for a CR product/upgrade? Or why bother. 🤔 But can’t you fit what you need at the back? 
Didn't @Beaky fit a fan to his rad he can switch on for added cooling in London traffic? Later car granted. 

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^ I did list a whole bunch of reasons already at the top and on the other thread.  

Here’s a recap:

1 - Thermostat is expensive and fragile.

2 - Oil lines expensive and get crushed. 

3 - Cleans up the side of the car if you don’t want cill covers or are doing a backdate.

4 - Removes the need for spendy backdate oil pipes when doing an SSI conversion. 

5 - Allows easier addition of a thermostatic fan as the electrics are right there in the engine bay.  

6 - Engine may well get to temperature sooner with shorter pipe runs.  Better for short journeys.

7 - Reduces the number of joins in the oil system so less prone to leaks.  I think I  can do this in just 8 connections including a modern thermostat.  

8 -  Allows installation of twin condensers at thefront of the car for better AC performance. 

9 - Saves some weight.  Although it moves it to the rear it is counter balanced with oil tank.

10-   because it seems like a fun project and something that is a least worth trying   

(edit.  Point 6 doesn’t hold)

I’ve always thought the external oil lines were a bit daft - sometimes evolution gives you an appendix.  

 

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It's annoying when people poo poo something you are trying to do isn't it........

I can see the merits of this system. I've always thought the oil pipes under the sill were a bit ugly but they do work well. I have two observations. I think then only reason someone is likely to change is when they are doing a complete rebuild otherwise the existing system is fine. Second, my concern, and I'm sure you have thought about this, is the filth that flies about in the rear wheel well. If you add shields to protect the rad will you not reduce then cooling effect?

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Posted (edited)
12 hours ago, Jonny Hart said:

27C7D272-014E-4512-BBF3-81C25E12BC53.jpeg.07c9f9722a45b36b2e0d076a4e041a76.jpeg

So that’s where we leave it, pending a couple of adjustments on fittings - need slightly different angles on the cooler. 

 

What is the thermostat attached to?  How are you going to get the cam cover off with it in the way?  Not poo pooing. Just asking 😊

 

Edited by Wingnonut

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I'm liking the install.  

I'm no engineer tech but won't that thermostat get a wrong read due to heat transfer from the engine/cam cover?  Also if you plan for early car install the rear bumper/valance area is much shorter than an IB so the cooler would need to mount higher into the wing space.

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My C3 had the trombone oil cooler. In the summer, stuck in traffic, the oil pressure would drop to the bottom of the gauge and the engine would get noisy and run a little rougher. so I know there is a need for some early cars to improve there cooling. I had a crushed tube to the front and ended up breaking the thermostat trying to remove the pipes, plus cutting one of the engine pipes off. I can tell you that the early 2.7RS to C3 oil pipes are very expensive. I know have new pipes, thermostat, 3.2 cooler and electric fan and bumper cut outs.

If a kit like this had been available, I would have jumped at it. Keep up the good work Jonny. All projects like this are interesting and fun, whether necessary or not.

Jason.

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@Phill Must be an oil thing. 😂   Either resto, SSI swap or upgrade from ‘trombone’ or SC type.  

@Wingnonut,   At the moment, it is just supported by the pipes and can be moved out the way quite easily for access to the valve covers.  I’ll probably design a stay to secure it but it’s not going anywhere!

@Nige, most oil thermostats on ‘normal’ cars are directly attached to the engine block.  The 911 already has one thermostat in the centre of the engine for the ‘onboard’ oil cooler.  

Noted on the rear quarter on early cars.  
 

I have elected to run my fan thermostat on the return line to the engine and have gone for 90 deg C.   The oil thermostat will let oil into the cooler at 80 deg C.    This gap should give me some idea about how often the fan is required and whether the cooler provides cooling unassisted at all.

 

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I’m looking forward to you posting this on Pelican Jonny, it will wake up all of the naysayers who went on for ages about your AC not being viable.......

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Hi Jonny,

What a great project, some really great engineering going on there 👍

Out of interest did you consider trying to mount the cooler in the engine compartment ? I think I’ve seen oil coolers on rally 911s mounted length ways in front of the fan. I guess they put it there, so less chance of getting damaged by flying stones etc.

P

 

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12 hours ago, Busybee said:


Didn't @Beaky fit a fan to his rad he can switch on for added cooling in London traffic? Later car granted. 

Yup, I fitted the Elephant Racing kit, you can set it up with a manual switch or control by a thermo switch.

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A couple of additional thoughts, will your rad and fan location compromise the use of wheel arch liners and will they be susceptible to damage from stones thrown up from the rear wheels? 

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This is interesting, if you are to develop a kit, please, if possible consider the engine swappers also. My shed is a 3.8 with two coolers up front with the required pipes connecting them, it's all a ton of oil, pipe runs, and connections in a car that sees some rough roads, and hard use. I can offer no insight as to its efficiency, but have had to fit fans on both rads, with bumper mounted scoops, and I still have concerns when at low speed. Its not even hot yet in SoCal............

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