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.

Radiator Leak Repair

Since first getting the car on the road there has been a very slight leak from the radiator bleed bolt.  I'd tried tightening it up a number of times, including using PTFE tape on the threads, but it always continued to leak.

I tried one more time, but unfortunately this time I overtightened the bolt and stripped the thread in the radiator - turns out the tread is just tapped into the aluminium so is very weak. My solution was to re-tap the  hole to a larger size (M10 x 1.5mm thread) and use a spare cap head bolt of the same thread that I just happened to have spare.

Once the bleed bolt was fixed I could get back to investigating the leak.  Upon closer inspection it was not the bolt that was leaking at, but a pin hole in the weld around it!  With the engine running drops of coolant would slowly form.  I decided to leave this for a while as the coolant was only coming out very slowly.

Many miles later I got a coolant overheat warning from the Webcon ECU.  Turns out there was air in the top of the radiator and the coolant was no longer flowing properly.  The cause was air being sucked back in through this tiny pin hole each time the engine cooled down.  Something had to be done to fix this. I took the front of the car apart and removed the radiator.  This was when I discovered that the pin hole had turned into a crack, probably about 10mm long.  The body of the radiator was starting to split.

I quickly took the radiator to the friendly local welders who re-made the weld over the area where the crack was.

I'm happy to report that after a few hundred miles of use there is no longer a leak in the radiator.  This gives me added confidence for longer runs, particularly with another trip to northern France booked for later in the year.

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.

Exhaust Clamp Tested and Rad Fan Switch Changed

Ran the engine again, this time with the silencer clamped to the cat pipe.  No leaks, so that job is done.

The radiator fan switch supplied by Tiger activates at 84oC.  This is a bit low for the Zetec on fuel injection so I always thought that I'd have to change it over to the higher setting.  Anyway, when I looked at the higher setting it was about 147oC so obviously no use!  I bought a replacement switch (Intermotor 50102 - for Peugeot 205/Citroen BX C15).  The lower setting comes on at 93oC and goes off at 88oC.  The higher setting is 97oC/92oC.  I installed it on the radiator and checked it in operation.  It seems to work okay.

As I have no thermostat installed I need the fan to operate at the correct temperature.  While running the engine with the car stationary the Tiger ali radiator seems to be very efficient at cooling.  I'll have to see how it performs when the engine is working harder on the road.  I may have to watch out for over-cooling, especially in the colder months.

Cooling System - Mark 3

When previously installing the Tiger alloy radiator I re-used the 'puller' fan that I had bought for the Polo radiator.  This meant that the radiator could not be angled back fully all the way to the upper horizontal chassis rail.  Now that I'm able to trial fit the nose cone I can see that the top of the radiator is not low enough.  Time to replace the 'puller' type fan with a 'pusher' type.

With the radiator angled all the way back to the chassis rail the nose cone now fits properly.

The water rail was attached to the side chassis rail.  A dab of Sikaflex and a rivet at each end have made a strong mounting.

Radiator Change

While at the Tiger at the weekend I discussed my plans for engine cooling.  Weighing up the pros and cons of the Polo radiator I had a change of mind and a further lightening of the wallet.  My car (is it a car yet?) is now adorned with a shiny alloy radiator.

This new radiator choice has also simplified the plumbing.  Now I'll just be using the two 32mm hose connections on the thermostat housing to the radiator and the 15mm connection on the bottom of the rad to the expansion tank.  Both heater outlets on the thermostat housing will be blanked and the centre of the thermostat removed.  It will take slightly longer to warm up, but as the car will not be used on very cold days it should not be a problem.

I've kept my 'puller' fan, but it means the rad has to sit a little high.  I will only know when I get the nose cone on.  There is probably a bit of room to move the rad lower with some slight tweaking of the mounting brackets.

Polo Radiator Fitted

Some simple brackets made up from 5mm steel strip.  B&Q had exactly the right piece of steel available from which to cut these.  The brackets were given a quick couple of coats of Hammerite.

Lightweight (tinfoil and plastic) Polo radiator fitted and fan mounted.  I decided to go for a 'pull' type fan in the end. This leaves the front of the radiator free for fitting an oil cooler later - no plans at the moment though.

The 12 inch fan fits in very nicely behind the radiator.

The radiator was mounted at angle for two reasons.  The first, as I don't yet have the bodyshell on I don't know how much space I have to work with, so erred on the safe side.  Second, if mounted vertically both the pipe openings clash with other things (steering rack and upper chassis rail).

The fan wiring will be connected once the wiring loom in the engine bay is properly routed and mounted.