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The Oil System - in Racing Cars

The Oil System - an Overview

Oil coolers are sometimes necessary on tuned and high performance engines.  The oil thins as the temperature rises and therefore its lubricating properties may be reduced. The oil temperature needs to remain at its ideal temperature or it will lose its viscosity.

If your engine (or gearbox) suffers from high oil temperature, fitting an oil cooler will help reduce this greatly.  However, a form of controlling the temperature increase and decrease should be considered so that the oil cooler does not over-cool the oil, which can be just as bad as over-heated oil.  There are two different ways of trying to control the temperature, the first is to have it so that the system is constantly flowing, and the second is to use a thermostat which will try to keep the oil at optimum temperature.

On race cars and special builds, a remote oil filter housing is sometimes a useful addition to your oil system. Standard engines will have the filter housing attached to the engine block. This is not always ideal given space restrictions in a competition car engine bay. Moving the filter on to a remotely mounted housing means that the oil filter can be accessed and replaced easily, somewhere more convenient, like a bulkhead for instance.

Go to - Oil System parts including Oil Coolers, Sandwich Plates, Cover Plates, Remote Filter Heads, Thermostats, Take Off Plates & more


Oil Coolers

The coolers are traditionally made in two matrix (core) widths, 115mm and 230mm.

We call the 115mm matrix “narrow” and the 230mm matrix “standard”.  Setrab also have a 310mm matrix which is known as “extra width”.  The 115mm gives an overall width of 210mm, the 230mm gives an overall width of 330mm and the 310mm gives an overall width of 405mm. The coolers are then sized by the amount of rows. These range from 7 rows right up to 50 rows.

As a (very) general guide, most applications will use ½” or -8 hose for the pipe work. Larger engines (V6/V8) may use 5/8” or -10 pipe work.  Some serious race applications or dry sump systems may use even bigger ¾” or -12 hosing and fittings. The bigger the hose, the more flow the oil will have in the pipe but be mindful that the restriction to flow will be the cooler.  Regardless of the size of the cooler or the pipe work running to it, the cooler tube diameters do not change, only the cooler matrix gets taller and/or wider. The surface area of the cooler dictates how efficient it will be. The bigger the cooler, the bigger the surface area, so theoretically, the more it will cool the oil passing through it. The image below describes how the oil and air flow through the oil cooler.

Our favourite Oil Coolers, and the ones we supply are from Mocal, Setrab and PWR, along with the Laminova Oil Cooler Heat Exchangers made by Mocal. Go to - Oil Coolers

Oil coolers are fragile components. Damage can easily be caused to the cooler if they are not securely mounted from vibration damage, over pressuring of the cooler and over tightening of the oil hose unions. The cooler should be mounted in a way that it cannot be damaged by vibrations. This means rubber mounting the cooler and making sure that the oil hoses running to and from the cooler are not under tension.

We sell various rubber mountings suitable for the job and also a professional mounting bracket made by SUSA which comes complete with rubber bushes and all mounting hardware. Go to - Oil Cooler Mounting Brackets & Accessories

Over tightening of the hose unions should be avoided. It is also extremely important that when tightening the hose union onto the cooler that BOTH the hex on the cooler and the hex on the hose union are held with a spanner at the same time. NEVER use just one spanner to tighten up the hose union.  As the image below highlights, the unions which are fixed to the top of the cooler are delicate and are attached to the cooler body by a thin plate. Not supporting this hex on the cooler means the fixing can easily be fractured which will undoubtedly cause the cooler to fail.



Sandwich Plates and Filter Heads

Depending on whether you have enough room, often the easiest way of plumbing in an oil cooler is to use a sandwich plate between the original oil filter housing location and the filter itself, we can supply the sandwich plate with or without a built in thermostat.  

Another way to plumb in an oil system is to use a sandwich plate with a cover plate, or use an engine specific take off plate and make the oil filter remotely mounted.  You cannot use a thermostatic sandwich plate in this instance as it would prevent oil from flowing round the remote filter when cold and unfiltered oil would enter the engine.  If you want to make it thermostatic then you will need to use an inline thermostat which can either be 'push on' or 'threaded' (BSP or JIC) and sits in the pipe work.

Please see the diagrams below for examples of both systems.

System 1: is where you use a sandwich plate which can either have a built in thermostat or not. If you are plumbing in your system this way then you will also require an extension bolt. The arrows indicate the direction of flow of the oil.

NOTE: Oil always flows up the centre of a filter.


System 2: is a little more complicated, again you will need a sandwich plate but this time you won't need an extension bolt, instead you will need a cover plate.  We sell the Mocal cover plates to suit most engine applications.  Below we show the correct way to install a thermostat into this system.  As mentioned, you can only use the inline thermostats on a remote filter installation.  You do not have to fit a thermostat if you do not require one.  A remote head will be needed to mount the filter.  We keep a wide range of remote filter heads, both Mocal and SUSA, with different in and out port orientations to give you almost infinite plumbing options.

WARNING:  When plumbing in a remote filter make sure you plumb it in correctly depending on the direction of flow. Some oil filters have a non return valve on them and if you have plumbed in your system incorrectly then you will prevent oil from flowing around the engine




Oil thermostats, as mentioned, control the flow of oil to the oil cooler. They are not always necessary but should be considered, especially on road cars. The thermostat works just like the one in your engines water system, only that it restricts the amount of cold oil that goes to the cooler until it reaches its set opening temperature.  When the oil reaches 80°C, it will begin to open the thermostat and the oil can then flow freely to the oil cooler.  Contrary to belief, it does not block all oil flow to the cooler when cold.  It still allows minimal oil to flow to the cooler when cold but because oil is thicker when it is cold, the oil will take the easiest flowing route, which at this stage is through the thermostat and back to the engine.  When the thermostat opens, the easiest flowing route is through the thermostat to the cooler and return.

The fitting instructions for the thermostat are below:

1. Select suitable place for fitting the thermostat away from moving parts and at a place where hoses run parallel.

2. With ignition turned off (high tension lead disconnected), turn engine over on starter and note which pipe carries the oil supply from the engine.

Connect up hoses as shown in FIG 1 below.


FIG 2, above, shows how the thermostat can be plumbed in on certain applications where the oil hoses do not run parallel for sufficient length for the thermostat to be fitted.

We stock a huge range of oil thermostats from both Mocal and SUSA. These are available with push-on, BSP or JIC hose connections.


Take-Off Plates

Much like the sandwich plate and cover plate method, a take-off plate is a neat way to install a remote mounted oil filter.  These are generally more engine specific than using a sandwich plate and cover plated.

Normally a take-off plate is a machined or cast aluminium adaptor which removes the original oil filter head entirely. It then allows the oil hoses to be attached directly to the engine, up to the remotely mounted oil filter head. These are also handy for engine conversions where the original oil filter location is hard to reach or would foul the chassis.

We sell a small range of take-off plates for generic applications as well as some BMW engines, BMC engines, Jaguar engines, Chevy V8’s etc.

We also sell a Rover V8 oil pump cover which replaces the standard unit for use with an oil cooler installation. The standard pressure switch and oil pressure relief valve should be removed from the standard unit and used in this Mocal item.


Go to - Oil System parts including Oil Coolers, Sandwich Plates, Cover Plates, Remote Filter Heads, Thermostats, Take Off Plates and more

See our other technical documents for information on Laminova Heat Exchangers and Accusump Oil Accumulators.

Archived in: Oil Coolers | Oil systems

22nd August 2019