Cooling System Updated (Again!)

1. As advised by Tiger I originally ran the car with no thermostat and no bypass plumbing.  I understand this is a fairly standard set up for race cars.  However, if quickly became apparent that the engine was being over cooled.
2. My next configuration had a thermostat with a 3mm hole in it as a bypass.  This worked very well all summer - the engine stayed at a constant 88oC, unless the fan needed to cut in.
3. Once the cold mornings of autumn arrived the engine started to run cool again.  Things were fine at lower speeds, but once there was a significant air flow through the radiator the coolant temperature struggled to maintain 80+ oC.  So I decided to introduce a full bypass pipe and fit a thermostat with no bypass hole.  To do this I had to fit a thermostat housing from an earlier Silvertop Zetec.  This was necessary in order to fit the coolant temperature sensor in a place where it would get a reading prior to the thermostat opening (as the Blacktop Zetec housing has no sensor holes and I'd previously had the coolant sensor in the main pipe to the radiator).  This set up generally worked very well, but there was one problem: somehow air from the expansion tank would make its way to the top of the radiator, which is higher than the pipe that feeds it from the thermostat housing.  A little bit of air would get trapped there each time the engine was run until there was sufficient air there for the flow of coolant to break down - not good.
4. So one more modification and hopefully the final configuration.  A 8mm hose barb was welded on to the top of the radiator and plumbed into the pipe joining the thermostat housing to the expansion tank. Now all works well.  Any air can return to the top of the system and an added bonus is that the hole coolant system is now self bleeding, which will help when I come to renew the coolant at future services.

Here is a schematic of my final cooling configuration:

8mm hose barb welded in to the top of the radiator.  It is just above parallel with the ground.  This is to allow it and the pipe to fit under the curvature of the nosecone.

Full routing of the new pipework (apologies for the poor quality mobile phone pictures, must use the proper camera next time).

C-shaped brackets were fabricated from aluminium strip.  These were fixed under the camshaft cover bolts and rubber lined p-clips were riveted to them.

Reintroducing a Thermostat

As I am not happy with how the cooling system is working (over-cooling) I am going to re-introduce a thermostat.  One option is to add a lower water rail and connect this to the bypass outlet of the thermostat housing.  Only problem with this is that the sensor for the coolant temperature is mounted in the main cooling pipe and would not read properly, especially during warm up.  I've read that the thermostat housing can be drilled and tapped so that the sensor can be mounted here, but I don't want to take a chance trying to do that with something made of plastic.

In the end I've gone for the option some other Tiger owners have adopted: a thermostat with a bypass hole for the warm-up phase.  I've used a 88oC thermostat from a Ford Focus 1.8 diesel (part # QTH316K).  Prior to fitting a 4mm hole was drilled through the outer edge.

The Tiger provided radiator fan switch was a 87oC type, so that was changed for one that operates at 92oC (Intermotor part 50200, used on Alfa 33's, Audi 80's, etc.).  I took the car out for a spirited drive yesterday afternoon.  55 miles approximately.  Once warmed up the coolant stayed very steady at 88oC.  When I stopped in traffic it rose to 92oC, at which point the fan was running.

So far I am very pleased.  I'd just like to test the car in colder and warmer conditions, with a bit of time stationary to make sure it's not going to get too hot.  I've got the temperature warning light on the Acewell digital dash set to 95oC so that should alert me if there is a problem.  There's also a coolant overheat warning displayed by the ECU warning light.  This is via the temperature sensor that is screwed into the engine block.  I don't recall at what temperature this activates.

During this whole process one thought did occur to me: if your car does not have a coolant warning light it would be easy to add one by using the second (higher) temperature setting on a dual-temperature radiator fan switch.

Sunday Drive

Had a great drive today with a fellow Avon owner.  130 miles in all.

Very cold to start with, especially on the hills, but it warmed up later on.  As I was still concerned about over-cooling of the engine I made a shield to block the airflow slightly to the radiator.  Can be seen in this picture taken at the breakfast stop.

Even with the grille partly blocked off the engine was still running too cool, so I will have to sort it out properly.