posted by
someone claiming to be gert
on
Tue Jan 6 07:35 CST 2004 [ RELATED]
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For cooling the recently fitted B20F in my 444 I want to try (and bought) an electric fan and therefore I had a provision made in the lower radiator part for mounting a thermostatical switch. Now these come in an enormous number of variaties (see for instance www.facet.it and enjoy the Italian language).
I was advised to try a 85/75 degr. C switch when a 82 degr. C thermostat is mounted. What do you think? And what do you estimate the temperature will be in the head when it is 85 degr. C in the lower radiator?
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Normally rad fan switches are fitted high up in the radiator. We used and ajustable switch on the 544, it just fits through the top hose.
Regards
Pete
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posted by
someone claiming to be gert
on
Tue Jan 6 22:37 CST 2004 [ RELATED]
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Peter, these switches are normally mounted in the lower radiator (except VW, but they use a 1,5 bar pressure). The reason for the low mount is preventing the fan to activate more often than would be necessary. At least so I was told by a specialist.
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I guess the smartarse response to that is "so what is this guy actually a specialist in?"
The principle behind this is simple enough, the hottest water wants to be at the top of the radiator, as it cools it will fall to the bottom. Indeed if the rad is tall enough, and the cooling system large enough, the cooling system will thermo syphon, as it does on many a vintage car, without using a waterpump.
The object of the exercise is not to keep the fan from coming on, but to keep the water at a teperature where it cools the engine to an acceptable degree.
It still seems sensible to me to react to the highest temperature, that of the water coming out of the head. It seems to me that if your fan reacts to the water temperature after it has cooled, potentially you could have excessive temperatures in the head.
At the end of the day it's your engine and your money. But I know what I'd do based on building many an historic rally car and sometimes learning the hard and expensive way.
Regards
Pete
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posted by
someone claiming to be gert
on
Thu Jan 8 00:40 CST 2004 [ RELATED]
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The guy is a specialst in radiators since 1977. What he says is that in low pressurised systems (as in our cars) the elctric fan will activate more than necessary (for instance when driving) when you mount the sensor high up, because temperatures there vary more than in the cooler and lower part of the radiator. Important is that the water is cooled sufficiently before it goes back to the engine. Around 10% of the car makers mount the sensor high up, but only on high pressure systems. So the question is, do we know better than them?
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Actually my take on this is that the important part of this is to get the engine to run at the right temperature, always.
As I said earlier the last rallying PV I built has the fan switch in the top hose. It also has a light on the dash to show when the fan is actually running, and an, on, auto, off switch on the dash.
Experience shows the fan normally only comes on in heavy traffic, towns or when being driven very hard in mountains.
I don't doubt that you can control the temperature by measuring the temperature of the cooled water. The fact of the matter is however that using a proprietary switch it will have been designed for something different. If for argument sake you use an 80 degree switch in the bottom of the rad you could end up sending water back that is either too cold, or with temperature control that is so marginal that if something hapens, like getting stuck in traffic, that you overheat. What I DO seriously doubt therefore is that you'll hit the right combination without experimentation.
Using such a switch you'd need to put it at the correct height in the radiator, and use the correct temperaure range for the cooling capacity of your radiator. Bear in mind also that most modern cars have crossflow radiators, In a standard volvo rad you can only put it in the top or the bottom.
If you use an adjustable top hose switch you know you're reacting to water that is actually flowing, and you're controlling the temperature your engine is actually reaching. Often modifying cars on a budget isn't about the ultimately best engineering solution, but creating something that works straight out of the box, at a reasonable price.
As I said it's your money, your engine, and you asked what we thought would work. This works.
Regards
Pete
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Personally I would prefer to have a fan come on too often than not enough.
If there was a reduction in flow through the radiator, then a smaller volume of liquid moving through the radiator would loose more BTU's than the design delta T. Therefore, a condition could occur where the temperature of liquid leaving the radiator will not exceed the fan-on setpoint of the sensor located on the discharge side of the radiator while the engine was not obtaining sufficient cooling _capacity_.
Of course, that condition is dependent on a compromised radiator. I never tested the flow or cooling capacity of my radiator and wonder how many people do. Perhaps having the fan come on more than expected could serve as a warning sign that something needs attention.
Just my 2 cents,
Joe in WV
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Pete;
...the sensor must sit low enough to be submersed in the coolant though, or else it may not sense when the fan needs to move additional cooling air...
Gert;
Which temperature sensor to use, and where, is a complicated thing which the engine design guys probably spend weeks measuring, checking, trying, etc. so just asking what the temp would be is oversimplyfying the problem...temp at any particular point on the rad is a complex thing influenced by a number of variables...that's why I'd just start out with whatever was stock for that engine in about the same location...naturally, an adjustable like Pete has will allow you to optimize...especially when the weather changes seasonally...
Cheers
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Ron,
I've got the sensor on mine in the upper radiator hose as well. If the thermostat is open, it's in the coolant, even if the radiator level happened to drop low.
Gert,
Hot water from the engine goes in the top of the radiator, and cooler water goes out the bottom of the radiator. It makes sense to put the sensor where the hot end of the system is, no?
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"It makes sense to put the sensor where the hot end of the system is, no?"
Actually, my thought would be that the fan only needs to be on when hot water is coming out the cool end of the system. Unless it is hot there there is no need for the fan to be on, regardless of how hot the water is at the hot end.
Of course, that being said the thermostatic probe on my electric fan setup is inserted into the fins of the radiator about 1/3rd of the way down.
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I don't know if this makes any sense, but...
I have an E head on my B20 (in a 122) and am running HS6 carbs, so no need to use the temp sensor on the passenger side front of the head. I also don't know if the F head heas a similarly fitted sensor (location), but could this be used to activate the fan Gert's installed? Or in lieu of that, would Pete's adjustable work in this location. It's "behind" the thermostat, so that might mess with reading temp into the radiator, but...
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