Thermo fan info

Joined: 25 Oct 2003 Location: Melbourne Australia

Thought this might be useful to some people eg when converting to electric fans.

Pinched from another forum.

Joined: 31 May 2006 Location: Bellarine, Brackistan

Thanks CB!

I have fake EL thermos with stock RRC rad cooling 350 Chev. Second fan runs on adjustable switch, first fan is on all the time which is excessive.

Sometimes in winter it doesn't even get up to normal op temp and I was looking for a cheap option to switch first fan on only when up to temp.

cheers, DL

Joined: 30 Dec 2002 Location: Adelaide

This might be of interest to anyone who is using dual thermofans:

Note the use of the Tridon 2FS 214 thermal switch which has two inbuilt switching points. (Info originally from here http://www.fordforums.com.au/vbportal/forums/html/showthread.php?t=57070&page=1&pp=25&highlight=wiring+diagram+AU )

I'm also currently converting my Suzuki XL-7 using a similar circuit, but instead employing two Jaycar Universal Voltage Switch to do the temperature switching. That way I've got adjustable switching points (and hysteresis) plus I can use the factory ECU temp sensor to get the reading. I'm using a Spal dual 11" thermofan with built in shroud- but the circuit would work fine for any dual thermos.

Joined: 31 May 2006 Location: Bellarine, Brackistan

That's great!

This should really all be a sticky.

Chimpboy............. how well do you know the big chimp?

Joined: 25 Oct 2003 Location: Melbourne Australia

Below are specs for Davies Craig thermo fans. Should do as at least a rough guide for other brands' current draw, cfm etc. One thing to note is that although a lot of people go for the dual 14" fans, the total flow is better from a single 16".

Joined: 30 Dec 2002 Location: Adelaide

I'd highly recommend checking out Spal fans over Davies Craig, they're a bit harder to find in Australia but there are some bargains on ebay.com Wink

http://www.spal-usa.com/

Joined: 25 Oct 2003 Location: Melbourne Australia

murcod wrote:

I'd highly recommend checking out Spal fans over Davies Craig, they're a bit harder to find in Australia but there are some bargains on ebay.com Wink

http://www.spal-usa.com/

For the record, I'm definitely not pushing these particular brands... just gathering together some rough data for people thinking of using electric fans.

Joined: 30 Dec 2002 Location: Adelaide

chimpboy wrote:

murcod wrote:

I'd highly recommend checking out Spal fans over Davies Craig, they're a bit harder to find in Australia but there are some bargains on ebay.com Wink

http://www.spal-usa.com/

For the record, I'm definitely not pushing these particular brands... just gathering together some rough data for people thinking of using electric fans.

Sorry, I wasn't suggesting you were! A lot of people don't realise there are a lot of higher performance fans out there- most people in Australia just naturally think of Davies Craig and don't look into it any further.

I was just adding on the link to add to the informative nature of the thread. Wink

There are spec sheets for the Spal fans on that website I posted so people can do comparisons for themselves.

Spal also make a larger selection of fan sizes (including dual 11" and 12" shrouded versions) plus straight/ paddle or curved bladed options.

Flexalite also make some high peformance fans and even have kits out for converting common USA model 4WD's eg. Jeeps. http://www.flex-a-lite.com/auto/html/electric-fans.html

Joined: 25 Oct 2003 Location: Melbourne Australia

murcod wrote:

I'm also currently converting my Suzuki XL-7 using a similar circuit, but instead employing two Jaycar Universal Voltage Switch to do the temperature switching. That way I've got adjustable switching points (and hysteresis) plus I can use the factory ECU temp sensor to get the reading. I'm using a Spal dual 11" thermofan with built in shroud- but the circuit would work fine for any dual thermos.

I have been thinking about this since you posted it... actually since before you posted it, mulling over the most logical relationship between the fan switch/temp sensor and the car's thermostat.

My thinking is that I am not 100% sure I like the idea of picking up the fan switching temperature from the engine side of the thermostat. I think it is better to have it on the radiator side of the thermostat. But I dunno. I would really like to hear all the different thoughts on these setups. I've even done a few saucepan tests of switches and thermostats to get the juices flowing.

First, some facts that I think are pretty solid:

1. It is the thermostat's job to be the primary ruler of engine temperature. Generally speaking a thermostat begins opening 2-3 degrees below its stated temperature and is fully open about 11 degrees later. So an 88-degree thermostat opens slightly at ~85 degrees and is fully open at ~96 degrees. Obviously different makes vary slightly. And some older thermostats may have both an opening and fully open temperature stated.

2. Assuming your coolant is sufficiently cooled by the radiator, the exact temperature that your thermostat maintains in the engine will depend a bit on the engine, water pump, radiator, etc. It won't necessarily be exactly 88 degrees for an 88-degree thermostat but it will be in spitting distance of that.

3. If your cooling system is right, your thermostat will never actually fully open. It will oscillate between fully closed and partly open, but if it gets fully open then you've essentially lost control of the engine temperature.

4. Slightly off-topic, but still a relevant fact - both engines and cooling systems are more efficient if the engine runs at a higher temperature. Basically the hotter the better as long as the engine design permits. Too hot kicks in when different metals expand differently (so bearings fall out or whatever), or when materials soften or warp. But there is no sense in any idea that cooler = better. Stable is the goal.

...

I think those statements are solid. Now here's my speculation. Purely looking at an electric-fan-only arrangement; if you have a mechanical fan as well then it's totally different.

5. The fan should switch ON at a temperature lower than the fully-open temp of the thermostat. So if the 88-degree thermostat is at approx. 85-96 degrees from closed to fully open, the fan should kick in at no higher than 96 degrees.

6. The fan should also switch OFF at a temperature higher than the fully closed temp. So, if you have an 88 degree thermostat that is at approx. 85-96 from closed to fully open, a fan switch that such as a 95-On, 90-Off would be the go.

7. If your fan switches OFF at a temp lower than the fully closed temp of the thermostat, it is pretty much going to run 100% of the time IF the temp sensor is on the engine side of the thermostat. That's the scenario that I think is not quite right, but it probably is okay if you have an adjustable switch and you adjust it correctly anyway.

I have fitted an 88-degree t'stat and a 95-on/90-off fan switch, with the fan switch in the t'stat housing on the radiator side. I can't report on how well it works yet but I am hoping it will maintain a pretty constant running temp.

Anyway, I could have this completely wrong. So what do you reckon?

Joined: 30 Dec 2002 Location: Adelaide

Yes, I'd agree with probably all of what you've said. A lot of those points you've mentioned are also why I'm going for adjustable switch on points and dual speed.

This is my second conversion and I learnt a lot from my first on my old Feroza. For a start don't use those harnesses supplied with fan kits (eg. the Davies Craig kits)- the wire is simply too small and drops too much voltage, even a slight drop will be very noticeable in fan speed. Use 6mm squared cable minimum.

I'm also going dual speed because that's what most modern factory setups do. It also means greater regulaltion control over the coolant temp - you're not trying to suddenly cool things once they are starting to get too hot (which is often the case with a single speed fan.) On my Feroza it struggled to pull the temp down on 40 + degree days with the A/C on.

The controllers I'm using are adjustable for switch on points and at the moment I'm monitoring what constitutes a "normal" coolant temp sensor voltage range with the viscous fan fitted. I'll be setting my low speed fan point at the top of this range and high speed slightly out of this range.

I'm doing the monitoring to ensure that I'm not "fighting" the thermostat (ie. cooling the coolant so much that it will be closing.) I know that the coolant sensor voltage oscillates around 0.545 -> 0.555V on cold days at 60km/h plus, so this would appear to be the set point maintained by the thermostat and i don't want the fans running when close to that range.

The factory systems also use the ECU coolant sensor (from what I've seen) which is in the block. However I can see the merits in possibly locating it at another point (eg. radiator outlet hose to determine if the radiator is cooling enough before the coolant enters the block.)

I dearly wish that my Suzuki was OBDII compliant as that would make monitoring everything so much easier. Instead of monitoring voltages I would be reading actual coolant temps. Crying or Very sad

Joined: 06 Mar 2006 Location: Melbourne-Australia

Tried the voltage sensitive switch system and found the following...

Little ecu coolant temp voltage variation at operating temp - The ECU coolant sensor is mostly used during warm up and is non linear. Had to completely remove the hysteriesis and disable the input divider

Variation in ECU reference voltage caused shifting of switching points with differences in electrical load.

Ended up going to a temperature controller ( jaycar again ) with a seperate sensor - now works fine.

Sooooo - check exactly how stable, what voltage and span is available from the ECU coolant sensor BEFORE you get too carrried away. Would work fine with some and be a PITA with others makes and models.

Also whilst im ranting.... have a look at the flow specs of a Davis Craig vs SPAL for example. When in free air they both appear to flow almost the same. But look at the figures when operating with a restriction - the Davis Craigs falls in a heap - a sign of pretty average blade design.

And...... there are blade sets for Push and Pull applications and it does make a difference. Anyone who says "one will do both" is probably just proving how bad their blade design is.

Joined: 30 Dec 2002 Location: Adelaide

For anyone who's interested I've got more info on how I'm doing my conversion on this forum: http://www.suzuki-forums.com/suzuki-vitara-grand-vitara-xl-7/22213-conversion-12v-thermo-fan.html

Joined: 30 Dec 2002 Location: Adelaide

MightyMouse wrote:

Tried the voltage sensitive switch system and found the following...

Little ecu coolant temp voltage variation at operating temp - The ECU coolant sensor is mostly used during warm up and is non linear. Had to completely remove the hysteriesis and disable the input divider

Variation in ECU reference voltage caused shifting of switching points with differences in electrical load.

Modern factory EFI systems use the same sensor to control the switching of stock electric thermos, and do so very accurately. So there's no reason why an aftermarket add on shouldn't work just as well.

Yes, I've found the factory sensor "normal" range with the viscous fan on is small (around 0.06V variation.) However that is the range measured with the viscous fan operating - so in theory the electric thermofan wouldn't need to be on until the voltage got somewhat outside that normal region.

I have modified the Jaycar circuit and have got the hysteresis down to around 0.025V which should be more than ample. The only reason why I've gone that low is because I'm using two controllers to give me dual fans speeds- if it was a single speed set up it wouldn't need to be that low a voltage difference.

The reference voltage shouldn't vary greatly and perhaps might be a vehicle specific problem?