Engine Plumbing

Why is Cooling important?

Generally Cobra replicas are running large capacity, high performance, expensive engines, as such, protecting your engine from overheating is vital.

Typical System Description

The cooling system used in the Sumo typically uses an inverted Seirra Radiator and expansion tank……


Pilgrim usually supply a pair of 10" Pacet puller fans (CHECK THE SIZE), these fit on the back of the radiator and "pull" air through the rad to cool it down. Pacet fans come with a set of fixings that consist of plastic tubes and things a bit like cable ties that you simply push through the rad by parting the metal fins. These generally work ok, but some owners have found that leaks can occur around the fixings, but one major draw back of these fixings is they are not reusable. If ever you need to remove your fans, the fixings must be cut off and replaced. This is a pain, but replacements are also expensive at around £16 for both fans.

A common alternative is to mount the fans on some simple brackets which can be fixed across the radiator and allow the fans to easily be removed and replaced at no cost.

The below picture shows how simple aluminium angle (B&Q) can be used to made simple reusable fan mounts:


The fans are controlled by a thermostatic switch which fixes into a threaded hole on the radiator. The switch simply grounds (connects to the chassis) the fans which are permanently connected to 12v thus completing the circuit. This may need to be done via a relay depending on the current rating of the switch vs the current draw of the fans. If in doubt, use a relay. (the more recent Pilgrim Loom comes with a relay fitted as standard)
You should check that the temperature at which your fans come on is suitable for your engine. Ideally the fans will come on at a temperature well above that of the engine thermostat but plenty low enough to protect the engine from over heating when stationary and running. A typical example if running an engine with an 82 degree stat would be to get a fan switch that comes one at 88degrees and goes off at 84 degrees. This will provide protection for the engine without you finding the fans are constantly running when not needed.

A nice feature is to add a manual override to the fans inside the cockpit, then should you find yourself in a traffic jam or running the car while stationary you can simply flick the fans on to prevent any unwanted build up of heat. The switch only needs one wire from the the fan side of the thermostatic switch which then connects to ground, see diagram below:


For the switch in the rad, there are a wide range of switches available:

Fan switch info

Radiator Mounting

The radiator is bolted directly to the chassis at the bottom, but at the top you will need to make up some simple brackets. This is just a case of finding a bit of steel, a bit about 10mm wide and 3mm thick is about right, then bending it until it fixes to the top of the chassis rail and the rad to make the radiator site nice and vertical. Its also a very good idea to fit something flexible between the rad and the bracket to take up any vibration. An idea solution is a pair of exhaust bobbins (available from all decent motor factors and even some halfords) The pictures below show such a pair of brackets.


Rover V8 Cooling

Below is a schematic of a typical Rover V8 cooling system as used in a Sumo:



With a standard Sumo cooling set up a problem can occur that the water being circulated by the water pump will not flow through the radiator, instead it finds the path of least resistance through the expansion tank, this can lead to greatly reduced cooling effects. A simple solution is to restrict the flow to the expansion tank for the water, this can be done by placing a simple restrictor in the bleed pipe that runs from the top of the rad to the expansion tank. One easy way to do this is to place a blockage in the pipe and drilling a 2-3mm hole it in, this will not restrict the bleeding of air, but will stop large amounts of hot water bypassing the radiator. This can be achieved using a piece of solid cylindrical plastic that fits tightly in the pipe, of depending on your hose size, some copper water pipe filled with lead with a hole drilled in it. The picture below shows another option to use an inline valve to allow the flow to be adjusted. It also shows where to place the restrictor. This position is good if you are using a blockage in the pipe as the flow of water will move it harmlessly towards the expansion tank.


Rover V8 and Edelbrock Performer Manifold Cooling Mod

A rather common complaint when fitting an Edelbrock performer manifold on a Rover is overheating. It be the case that even after setting up what seems like a perfect cooling system in your Sumo, bleeding all the air out, fitting the restrictors etc it still over heats. This can be caused by hot-spotting. The Edelbrock manifold has a number of water channels in it that bring the hot water up from the engine to flow out into the rad. What can sometimes happen is this very hot water can get to the temp sender and give a very hot reading, BUT, not get to the thermostat and so it initially stays shut. This can be seen if you invest in an infra-red heat gun, you can find that some areas of the inlet manifold are very hot, others quite cool.
If you find your car is overheating after what seems like a very short time after starting, this could well be your problem, before the engine is even properly warm the sender is surrounded by very hot water but your stat isn't opening. It doesn't seem to be consistent across all cars, some suffer from this, others don't. If you do, the fix is to apply a simple mod to the inlet manifold.
The original inlet manifolds fitted to the Rover SD1 had a couple of small holes within it to allow water to circulate and even out the temperature even when the stat is closed. To put a couple of these holes in an Edelbrock performer is pretty simple and can be done without even removing the inlet manifold.

This is how you do it:

  1. drain the system of coolant down to a level that the stat housing can be removed.
  2. remove the stat housing and stat.
  3. check you have a stat with a bleed hole in the flange, if not, while its out you may as well do this, simply drill a 4mm hole in the main flange and when you put it back make sure this hole is at the top.
  4. carefully examine the inlet manifold to see where the channels are, you are aiming to connect the main central chamber with the tributary water channels either side with small holes.
  5. Once you are confident you are not going to do something silly, use a 4mm drill, place it into the inlet manifold so its pretty flat and at about 45 degrees to the direction of travel of the car.
  6. Carefully drill both sides. Pictures below of the holes:
  7. Now you need to get as much of the swarf out as possible, you can use all sorts of things to do this, sticky tape on a stick, bluetac etc. Be careful if you decide to hover it out as it will create a lot of turbulence and may push the swarf further in. (remember that trick where you try and blow a feather into a milk bottle?) Another method is to put the stat housing back on without the stat fitted, and over the end if it put a baggy bit of cloth (ladies tights are perfect) then push the top hose over the tights so there is like a little fishing net in the top hose. Fill with water and run the engine, the flow will push all the swarf into the tights. Stop the engine after a minute, drain and you should find the tights full of all that swarf.
  8. Once done, refill with coolant mix.

You should now find the temperature is far more even across the inlet manifold and shows a more accurate and steady reading on the gauge.

The radiator used for the Sumo is from a Diesel, 2.3l Sierra. These might be available from these guys for a good price: Northern Radiators

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