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Reversed Coolant Manifold

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Site last updated on 15/08/08

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  Reversed coolant outlet manifolds reposition the radiator feed pipe from the LH rear corner of the engine (as installed in a rear engined vehicle) to near the starter motor, This is done by turning the manifold around 180 degrees. However, they do not fit as standard when reversed. The solution is to cut the manifold up, and tig weld it back together to make it a slightly different shape. The gap which the repositioned coolant outlet has to fit through on some engines is very tight, so RJES reversed coolant manifolds are cut and welded in fixtures for accuracy.   


   Standard coolant outlet manifold points towards LH rear light:










  Reversed coolant outlet manifold points past starter, towards T25 pipes:



  Reversed coolant outlet manifolds have a number of advantages. They:

  • Simplify the coolant plumbing on installations where the radiator is installed in front of the engine
  • Help to make the installation look more ’factory fitted’ - no long runs of pipe / hose visible in the engine bay.
  • Can make the coolant system easier to bleed
  • Allow the installation of a header tank system which actively purges air from the coolant as the engine runs
  • Point the coolant outlet directly at the radiator feed pip in a T25. Convoluted rubber hoses are not needed, as a piece of straight hose fits fine

   Reversed coolant outlet manifolds are suitable for use on all four cylinder Subaru engines. Due to the large number of variations in fuel system plumbing, etc. on different model engines, they can not be guaranteed to clear the fuel pipes on every engine. However, they are known to fit naturally aspirated 2.0. 2.2, and 2.5 engines from 1990 - 2000. They probably also fit many others, and if they don’t, maybe one fuel pipe will need re-routing. Some lengthening of the wires to the temperature sensor(s) fitted to the manifold may be necessary, but extra length can often be ‘freed’ by unwrapping the conduit and tape from the Subaru engine harness.

   RJES reversed coolant manifolds also come with the heater feed pipe repositioned to a natural high spot near the outlet. This helps make a self bleeding system, and solves the problem of the original Subaru steel heater pipe fitting fouling the induction manifold when reversed - the location of the original steel pipe is blanked off. Plumbing so all the heater coolant flow goes through the header tank is highly recommended, as this helps the system self bleed. This requires the header tank to be repositioned (for a neat installation). We also make a bracket to reposition the header tank at the front of the engine bay, on the right hand side.

Temperature Sensors:
  Early models have a separate tapping for the coolant temperature gauge in the dash. This is the small sensor with a 1/8” BSP thread (strange, on a Japanese engine). Later models use the signal from the ECU to drive the gauge, so don’t need the second sensor.
  You are fine using a late model manifold on an early engine, if you don’t need the standard Subaru temperature gauge. If you are fitting an aftermarket gauge, you can drill and tap the manifold boss to suit.
  If you fit an early manifold to a late engine, you will have an extra 1/8” BSP tapping. This can either be used for an aftermarket gauge, or blanked with taper thread 1/8” BSP plug, or the Subaru original sensor.
NOTE: 1/8” BSP is very similar to both M10 x 1 and 1/8” NPT - so close that they will go in for a turn or two, but the pitch is NOT the same. Using either of these is very likely to strip the thread

 Inventors of the Subaru - VW conversion bell housing using Subaru flywheel, clutch and starter

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