Home Up Getting Started Cooling System Air Intake System Auto Tranny Eng Support Eng Damper Instrument Cluster Cruise Control Speed Sensor Timing Belt

         Cooling System Planning

Updated - 2008 November 09

As you start to get into your Subaru conversion, one of the key areas to pay attention too is the cooling system. A number of cooling system configurations have been used - there is the KEP configuration that works well but is quite a challenge to bleed. The current Small Car configuration works well but some people in our colder climates have had concern about the engine running hotter when the heaters are removing a lot of heat. To address the fact that the EJ22 engine does not have a dedicated thermostat housing and to address the cold climate concerns, I have designed a separate thermostat housing and am using this in my 86 8 passenger conversion that I am working on in early 2005.


Based on Warren's comment I have revised concept 3 to put the burp tank in the heater circuit and thus eliminate any heat loss in the thermostat circuit. This is our best effort so far:

This configuration is implemented in our engine test stand and works very well with about 15 Deg F temperature drop in the heater coolant returning to the water pump - engine temperature stays steady.


- the line to the dedicated thermostat housing should not be larger than 1/2 inch. This 1/2 inch line provides all the heating necessary to open the thermostat in cold weather.

- The connections to the heater circuit should not be any larger than 5/8 in. In cold climates, if this connection is any larger, and the heaters are On full blast, the engine may never reach proper operating temperatures.

- The valve in the SC type bleeder line can be very small 1/4 or 3/8 inch ball valve. This valve can be closed after the air is bled out.

Refer to Cooling System Kit - Cooling System Kits

2008  - Concept 5 Cooling System Configuration:

This past summer I converted my 1985 Westy to a Subaru EJ22 engine  For this conversion I wanted to experiment with a further refinement to my cooling system arrangement. The one concern I had, about the concept 4 above, is that when both heaters are turned Off there is no flow through the pressure tank - thus trapping air in the pressure tank is not as efficient. So concept 5 puts the pressure tank in the thermostat housing circuit using 1/2in  ID heater hose for the connections. The initial filling of this system and the bleeding was very straight forward - with no need to elevate either end of the Vanagon.

Modified the diagram and added a bit more info.

Refer to Cooling System Kit - Cooling System Kits


This is what my engine bay looks like with this Concept 5 cooling system.



Here is another very successful cooling arrangement using the dedicate Thermostat housing:

This is the configuration that Peter/Dieter used and they have reported excellent heat from their heater with No overheating of the engine in very cold weather. They are going to modify their Syncro skid plate to avoid the interference with the thermostat cap.   Thanks goes to Dieter and Peter Miller for their testing and feedback.


Here is what my thermostat housing looks like:
This picture shows the thermostat housing loosely assembled to a water pump.


For details regarding the  thermostat housing please click -  Thermostat housing

A small quantity, of the housing, are available for purchase.

By the way - do not be fooled into using after market thermostats. The small after market one was removed from an EJ25 vehicle I was servicing - with cooling problems. USE OEM THERMOSTATS only.    
 NOTE: Use these ideas at you own risk - no warranty or guarantee implied or included.  Tom    
Home Up Getting Started Cooling System Air Intake System Auto Tranny Eng Support Eng Damper Instrument Cluster Cruise Control Speed Sensor Timing Belt