2.4l Opel 8V CIH Competition Engine

Oil & Water Cooling Systems

The oil system is fitted with a sandwich plate above the oil filter allowing the oil to flow through a 13 row oil cooler before it enters the engine.  The sandwich plate does not have thermostat control, but this is easily changed if necessary.  The oil cooler sits directly in the airflow to the radiator.

The cylinder head and thermostat housing fitted to my 2.4L CIH engine are from the Vauxhall Carlton 2.2L, as is most of the radiator pipe work.  The radiator is from an early 2.0l 8V Vauxhall Astra, which is modified and has a 4 row staggered core.  The radiator air intake area has been made bigger and boxed in.

Water System Problems and Solutions

During initial running in of the engine, we found that the engine water temperature ran quite hot (at around 90°C), compared to my old 2.0L engine.  We also found that  the water temperature was very stable while the car is moving, even at high RPM.  This is almost certainly due to the air intake area being bigger, and the radiator having been boxed in, so causing extra air to be directed through the radiator.  However, at tick-over, even with the outside air temperature down to less than 5°C,  the water temperature was only just being kept stable, even with the electric radiator fan running.  This was obviously going to be a major problem during the summer.

From the rolling road testing at Emerald Cams in November 2000, we found that the water temperature needs to be kept below 85°C, because above this temperature, the engine immediately looses about 10BHP.  At this time, the engine was still fitted with the original Carlton 2.2L 92°C thermostat.  So, we have immediately found why the engine is running hotter than the old 2.0L engine, which had an 82°C thermostat.  We decided that the 82°C Manta thermostat would be cutting it just a bit to fine, but we managed to find that a 78°C thermostat from a Porsche 924/944 engine was very similar to the Manta/Carlton thermostat.  This new thermostat immediately brought the water temperature down to about 80°C, which is a gives a reasonable margin below the 85°C upper limit.  However, the cooling system was still only just coping at tick-over.

From discussions with the guys at Emerald Cams, during the January 2001 visit,  I learned the following:-

1.    At tick-over, say 1000 RPM, the mechanical water pump is very inefficient, and does not pump enough water around the cooling system to cool a modified engine properly.

2.    At high RPM, the mechanical water pump is pumping too much water around the system, and the thermostat partially closes to keep the engine temperature up.  Also at this high RPM, the engine power loss due to pushing so much water around the engine becomes very significant, and can be as much as 10 BHP.

firstly, I thought of replacing the old copper cored  radiator, with a larger, higher capacity, alloy radiator, which because it was alloy, would have a much better heat transfer rate.  However, it was suggested that I should fit an EWP electric water pump and controller to the engine, to replace the mechanical pump.  It was thought that this would alleviate the cooling problems at tick-over and also give needed extra power at high RPM.

The Electric Water Pump controller monitors water temperature in the engine block, and adjusts the speed of the pump to increase or decrease flow accordingly.  This means that cooling will no longer be dependent on engine speed and should be less dependent on air flow through the radiator.

Power loss due to the mechanical water pump is quite significant at high RPM, and cooling on a modified engine is often inadequate at low RPM.  In the case of my engine, fitting a new low temperature thermostat is not adequate at tick-over, unless the radiator fan is running even at very low outside temperatures of 1-2°C, so it has no hope in mid-summer.

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Last updated: Saturday, 26 July 2003.