coolant circulation.

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coolant circulation.

Post by tomsheppard » 16 Jan 2003, 17:03

During the great fault tracing session of the last month, it has been a source of some frustration to find that bits of the cooling system suffer from some rather amusing design faults. Things like putting the thermostat in a potential air lock. Or putting the warning light switches in a potential air lock. Or putting the heater up higher than the filler cap. (cure: raise front of car with crane to 89 degrees from horizontal before filling system but remember to open the heater valve. A piece of old carpet for the rear bumper to rest upon will protect it from scratches...)Or failing to put in a temperature gauge at all. Or wiring the thermostatic fan to run only while the ignition is on. Or routing the bypass hose to the bottom hose side of the radiator so that it not only air locks the rad but prevents the thermostatic switch from working at all. The general upshot as you all know is that you need a new head gasket (or, I dread, the head itself...) and a new rad. Once my car is operational, I shall be flushing the whole system annually, you can be sure and still I shall remain in ignorance of what is really going on. What is needed is some idea of the overall cooling system behaviour. Hard wiring the cooling fan earth to a good sound earth would be good for the peace of mind as well as Running a good fat lead from the battery to the fan switch feed via a big fuse so that the fan can do its work with a minimum amount of interference from the car. Somehow though I need to find out if the stat is air locked. Here is an idea. The temperature in the bottom hose must always be lower than that in the top hose if all is well. While the stat is shut, this may not be the case because of the return from the bypass hose.It certainly isn't the case if the rad air locks. Take two pieces of aluminium pipe and tap them for sensors.Place one pipe in top and one in bottom hose. Send the outputs of the sensors to a little circuit that can register the hotter one. (This is easy for me, I can do electronics.)Turn on a light when the bottom hose temperature is greater than Top hose temperature. Bingo! Cooling system warmup light.
Will it work? Discuss.

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Post by AndersDK » 21 Feb 2003, 06:44

Dear Tom !
Amazing how many Cit lovers have their background in Electronics !<img src=icon_smile_big.gif border=0 align=middle>
I would'nt bother all the mechanics involved in your idea.
2 pieces of NTC resistors (say 10Kohm/25deg) in series between +12V & gnd - 1 placed surface on lower hose - 1 placed surface on upper hose.
Fixed to hoses by a couple of windings gaffer tape - then 1 winding of water resistent insulation (foam insulation tubing) taped on top of this, to prevent false temp sensing.
A simple opamp circuit then compares the midpoint voltage of the NTC's to a set reference - some antinoise (RFC) components mixed into the circuit - and an indicator (hi-intensity) LED - and you're up & running. You may even add a piezo screamer to really wake you up when calamities are coming up. <img src=icon_smile_cool.gif border=0 align=middle>