Electronic Cooling System Control

Cooling Control Unit:


As the Tatra is an air cooled engine, it is fitted with a control box to control if the air intake fan runs or not.
How it is supposed to function is that it monitors the engine temperature and oil temperature, once the engine head temp reaches 150 deg  a voltage is removed from an oil valve that allows oil to drive the cooling fan,  thus if the system fails the fan runs all the time.

There is a light on the dash that tells you the system is working or indicates a fault.
Here is a picture of the said control box,  very industrial looking isn't it.

The fan on my truck was running all the time, however the warning light was not working either,

I started my investigation by checking continuity from the control box to the various sensing elements, there are two temperature sensors on the engine heads, there is an oil temperature sensor, there is a wire to the oil valve for the fan and there is a wire to the warning light.
There is also a ground and a +24v

All of these connections were present at the control box except the 24volt from the ignition, on further investigation i discovered this wire had been taped up inside a loom and never connected. Furthermore there was no bulb in the warning light.

Once i had connected the control box to the 24v feed and put a bulb in the light all was well.  So that's the cooling control working as it should.




The alternator charge light:

This little problem was really easy to fix,  the warning light had broken at the back and the bulb holder had fallen to bits, i checked all the wiring, it will be sorted once i replace the part.

Electrical issues, Temperature Gauge

Since i collected the truck i have noticed a few minor problems with electrical things not working at all or working incorrectly.  What i have spotted so far:

Temp gauge not working.
Oil light not working.
Alternator light not working.
Electronic cooling controller not working correctly


Temp Gauge

I verified that the temp gauge it's self was working first, then i identified the sensor on the engine block,  remember this is an air cooled engine so the gauge reads engine head temperature from a sensor directly in one of the cylinder heads.
There are two more similar sensors the signal a control box that controls the oil clutch of the engine cooling fan. The control box also monitors oil temperature
A simple test is to remove the wire from the sensor and short it to earth, the gauge should move to max,   It didn't.

So i started tracing the wire from the gauge to the sensor,  i used a tone sender that is used in the telecoms world, after a lot of dismantling and loom stripping i finally found the wire i was looking for,  of course it changed colour twice just to confuse me.   But i finally tracked it down, it was at the back of the engine instead of the front where it should be, just taped up in a loom not connected to anything. It took me the whole day to sort this one out.


Loom stripped to reveal the elusive wire.

 The wire where it shouldn't be.

Air Leaks, Continued

Most of the air leaks are now eradicated,  I am just waiting on some parts to finish the job.

This job has been a lot easier than I originally thought,  the main cause of the problem was fibre washers in the pipe joints were either just worn or had become two compressed and got loose.

Apparently I am told that this fibre washer system is an old way of doing it,  you would think that by now someone would have invented a better material to do the job, but it appears not.

So I got a big box of fibre washers and pipe fittings and doughty seals and off I went.  It's all a learning curve, I have never worked on pneumatic systems before.

I am sure it would be easier if the fittings were all BSP instead of Metric, it is very hard to get metric fittings here.

I also managed to tidy some of the wiring that seems to have evolved on the truck whilst I was at it.

It's looking a lot better now.

This is the old valve, i removed it cleaned and painted it the refitted with new seals

 I Added a silencer to the brake blow off circuit.

 Looking a lot smarter, and not leaking