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disabling cooling fans in very cold weather...good idea or not?

XJ XJ6 / XJR6 ( X300 ) 1995-1997

disabling cooling fans in very cold weather...good idea or not?

 
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Old 12-16-2018, 12:59 PM
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Default disabling cooling fans in very cold weather...good idea or not?

Hi, the next 3 months where I live are going to be mostly below freezing temperatures. My 95 XJ6 has the cooling fans hard-wired on all the time.

My idea is to remove the two 30-amp cooling fan fuses (11 and 17 in driver side) for these 3 months and run the car without cooling fans. This will: 1) let the engine warm up faster, 2) help batteries charge faster in short drives.
I do lots of short drives and maybe this will also warm up my feet faster

Is this a good idea? Especially when weather approaches 0 degrees Faherenheit in January and February...

thanks for the comments!
 
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Old 12-16-2018, 01:06 PM
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Nooooope

The fans will only turn on when the coolant rises above X degrees and the second at Y degrees ( negating the AC pressure switch Mod )

A cooler ambient ram air movement will bias it to a later spot in the engine power load regime with the fuses still installed

With no ram air at a stop depends on the temp of the engine coolant at that time and the need to get it down to operating tempdroping below Z gegrees

The thermostat in the coolant flow will keep the coolant from drooping below Z degrees negating skin heat transfer from the block

 

Last edited by Lady Penelope; 12-16-2018 at 01:34 PM.
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Old 12-16-2018, 01:16 PM
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I'd say that's a bad idea. If you get stuck in a traffic jam then the engine will likely overheat as you will be disabling the over temperature triggering of the high speed fan setting also.

You can easily make a mod to the car by cutting the wire jumper on the original Jaguar mod for the air con and attaching a toggle switch between the two wires. I've done this and have the switch mounted under the steering column. That way you can have the fans off if you want to but be able to turn them on if necessary also.

Picture shows the wire you are looking for (this is RHD car). You can test you have the right jumper wire just by unplugging it - the fans should stop.






 
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Old 12-16-2018, 02:24 PM
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I removed just fuse 11 (not 17 also)...this keeps the fans from turning on when I put key on and maybe helps batteries crank on super cold weather starts (my Jag doesn't have a warm garage).

Maybe the fans will still go on if the engine requires it (get some juice through other circuit, fuse 17 in parallel whnm thermostat switches).

I'll just try it for a bit in very cold weather and keep an eye out on engine temperature. I barely every sit idle with engine running...traffic jams not a concern.

thanks!
 
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Old 12-16-2018, 03:38 PM
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There is zero chance of the car overheating in freezing temperatures with fan disconnected, even in traffic, I've tried that and the car indeed heats up a little quicker, no problems at all. I've simply pulled the plug at the fan socket instead of removing the fuse.
 
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Old 12-16-2018, 06:10 PM
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That old x300 6 cylinder is BULLET PROOF!
Fix the fan relay its 15 dollars...…..
That way it will come on when needed.
gtjoey1314
 
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Old 12-16-2018, 07:55 PM
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I have the problem of my fans running all the time, and have not gotten around to diagnose the cause. If you choose to disable the fans, I think you should add a switch as shown. The x300 temperature guage stays at N over a wide range of temps, so by the time it started moving north it would probably be higher than you would like. Also with my issue I have noticed if you pull one fuse neither of the fans will work.

My car still warms up just fine now that I have a new thermostat installed.
 
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Old 12-16-2018, 09:08 PM
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96X300 ,

Remove the 4 wire connector on the high freon pressure switch and see if the radiator temp switch responds to give you the left fan only and both fans at the high coolant temp ( hard to get that hot )

The 4 wire high pressure switch is just aft of the 2 wire low pressure switch ( purple arrow in B1mcp's pic )

The fan control module is under the car just Fwd of the left front tire and can fill with water like mine

I developed a test months earlier on how to test the radiator temp switch and fan control module separate from the AC pressure switches

The instrument temp gauge is the single wire temp sensor next o the 2 wire sensor used by the ECU only , that is located atop the thermostat housing

The single fan will be on at all times with the jumper wire mod done

See the TSB as the jumper wire Mod seen in B1mcp's pic :

http://www.jagrepair.com/images/TSB/...%20Failure.pdf

Sometimes the 2 wire low pressure freon switch will not be installed

 

Last edited by Lady Penelope; 12-17-2018 at 09:26 AM.
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Old 12-17-2018, 09:10 AM
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gtjoey: i can't just fix a relay. the problem is that my car is hard-wired to have fans on all the time, but only when the key is on (a common xj6 hack done by Jag dealers).
The did that because before that, the fan would keep on going after the key was out and possibly drain the battery while "cooling" the engine faster...
 
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Old 12-17-2018, 09:11 AM
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the cause is a dealer "fix"
 
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Old 12-17-2018, 12:45 PM
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But won't the thermostat insure that the motor won't go below 180 ? Regardless of the fan's operation?
 
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Old 12-17-2018, 03:01 PM
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I would think the radiator, water pump, and properly working thermostat should be able to keep the engine cool... in freezing condition.
Obviously the engineers realized it's not enough in warmer weather and so they added a radiator fan.
I'll report back in a week how the experiment turns out.
 
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Old 12-17-2018, 10:56 PM
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I've driven my car in very cold weather (coldest was -44C) and the only mod I did was unplug the white jumper wire mentioned above. It is surprising how the temperature can rise in stationary traffic, I have had my fans come on in -10C weather, even with the heater on. Don't forget the AC runs in the winter to dehumidify the air, and that puts a heat load on the cooling system.

Regarding starting, I used the largest battery that fits in the tray, I think a group 49. It weighed nearly 60 lbs! That was standard fit for Canadian cars, and combined with 0W40 oil I never had trouble starting, even in -40C temperatures.
 
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Old 12-17-2018, 10:59 PM
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Originally Posted by smartobject View Post
But won't the thermostat insure that the motor won't go below 180 ? Regardless of the fan's operation?
Only too a point. In very cold weather on the highway with the heater pulling out a lot of heat it is possible to lose more heat than the engine can generate.
 
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Old 12-18-2018, 05:57 AM
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Originally Posted by madijag View Post
I would think the radiator, water pump, and properly working thermostat should be able to keep the engine cool... in freezing condition.
Obviously the engineers realized it's not enough in warmer weather and so they added a radiator fan.
I'll report back in a week how the experiment turns out.
It will keep it cool, nothing to worry about, even in summer that top fan is mostly there for AC as x300 doesn't have its own AC fan like the XJ40 used to have so have it disconnected during summer and you'll possibly loose refrigerant in traffic due to pressure build up in the system.
I've driven my previous x300 with both fans off in winter, it never went over 90C, even in Cambridge traffic, I usually disconnect the top fan as soon as it gets cold so no problems with AC. I've driven XJ40 with both fans off(as the sensor in the radiator died on me) and it was also fine, even in summer in traffic on german autobahn, although that one had the AC fan.
 
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Old 12-19-2018, 10:05 AM
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I tried pulling the fuse to stop the fans when the outside temp started getting down to 40f degrees.
The engine started smoking from the exhaust manifold area and looked like it was gonna overheat so I put the fuse back in.
The temp gauge is always way below N. Sometimes even into the blue.
I haven't figured out what's going on.
I have heat. I don't over heat. The car runs fine.
I noticed, when I first checked the car out that the AC was on but it was still kind of warm and humid in late September.
The car ran fine and the temp was fine but the AC was on.
The guy I bought it from actually delivered it to me.
He drove up from Warwick to Providence so it had plenty of time to overheat if it wanted to.
The AC, I noticed, was still on when he arrived and handed it over to me.
The next day, my first day as a lion-tamer, I turned of the AC and the car started to brew up!
I shut it off (I noticed that the electric fans weren't coming on).
I looked up the fuse situation online and found the correct fuse panel and noticed that one of the 30 amp fan fuses was pulled out and sitting right there.
I put the 30A fuse in and both fans came on.
They're always on until I shut of the car.
WTF?
I'm not comfortable seeing the water temp. gauge riding so low but I realize it's not really a gauge. It's a switch. A true "idiot light".
The car runs fine and only wants to overheat when I disable the fans regardless of the outside temp.
I don't really want to drive it in freezing weather if the engine isn't at the correct operating temp.
I figure that if I have heat then the engine is at least warm enough to give off heat , but it still makes me a little duck-billish.
 

Last edited by Jimi Shelter; 12-19-2018 at 10:10 AM.
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Old 12-19-2018, 10:32 AM
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Testing of the AC pressure switches portion only of the fans control :

Remove he 2 wire freon pressure switch connector and jumper with a paper clip , This will give you the left fan only

Remove the 4 wire connector on the other freon pressure switch and jumper any colored wire to any black wire and this will give you both fans

There are 2 colored wires in the 4 wire connector and the other one disengages the compressor clutch during freon overpressure so no harm in picking wrong colored wire

The current through these switches is small and not the high power current spinning the fan motor

No need to run engine for test , just key on
 

Last edited by Lady Penelope; 12-19-2018 at 10:35 AM.
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Old 12-20-2018, 06:09 AM
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Thanks for that, Lady P.
I'll try that.
I would like to know more about the relationship between the fans and the AC system.
It seems like it's all tied together somehow.
Having the AC on and preventing the car from getting overheated seems counter-intuitive to me.
I've always thought that if an engine gets hot I should turn off the AC and crank the heat on full blast to
get the heat out of the engine, but this system seems different.
I drove it in to work this morning (50 miles, almost 40 degrees outside at 5am) and , as usual, I had heat, the gauge never hit N, but ran just fine.
Once the salt and sand hits the roads, Mr Lion is going to hibernate for the winter
 
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Old 12-20-2018, 08:58 PM
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The priority of the radiator cooling fans is to prevent the engine from overheating by passing more ambient air through the radiatorhave

The secondary is to move enough air though to the A / C condenser behind the radiator to keep the cabin cool under various cooling demands / Freon pressure increases

The test of the engine coolant temp switch, Not to be confused with the 2 coolant temp sensors atop the engine coolant thermostat housing :

Remove the 3 wire connector on the engine coolant temp switch on the lower aft left side of the radiator .

Put a paper clip on the White wire to the black one and you should get the left fan only

Put a paper clip on the White / Blue wire to the black one and you should get both fans

If the TSB mod has been done you will always have the left fan on with key in the on position

If you don't get a right fan you can bring that fan motor connector over the the left and if the fan runs it proves the fan control module works as well as the high temp position on the 2 position temp switch

To test the temp switch you would have you remove it and dunk it in a cup of boiling water . At this point the White / Blue pin to Black would be closed with a meter check or zero resistance

As you put a ice cube in to cool the water the pins should open with the meter soon . 100 C

Over on the White pin to Black should be closed from the beginning boiling point and open as the water gets cooler . 86 C

The inter relationship between the 2 control systems when things are not working perfectly are :

You can turn on the cabin heat and this will act as a mini radiator to cool the engine block

By turning on the A/C you will command the left fan on only if the TSB has not been done , and if enough freon pressure is generated by cooling load you will get both fans .

Since the ambient air must first pass through the radiator before the condenser the effect is you'll get that missing radiator temp commanded fan/fans

The counteractive part is by turning on the A/C in the driveway the RPM gets bumped up a bit by the A / C ECU to the engine ECU hence generating more engine block heat

This all changes as the car moves and you have ram air passing through the radiator / condenser

The newer coolant thermostats fail in the closed position opposite the fail passive or open of the past . Now add that to your heat balance equation which in reality what your looking at in a big picture

By the thermostat failing closed the engine coolant radiator and fans are removed

Editing
 

Last edited by Lady Penelope; 12-20-2018 at 09:54 PM.
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Old 12-20-2018, 09:21 PM
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The FIX with the 'jumper-wire' was to address the problem of the low speed blown-fuse issue. The JUMP to HIGH SPEED without the fans first being in LOW SPEED would blow the 30 amp fuse and the fans would be disabled causing over-temp.

The fans PERMANENTLY being in LOW SPEED would alleviate this issue.

You might want to drive VERY SLOWLY to not have airflow through the radiator to duplicate the fans being disabled!!!
Fans ON and driving more than about 40 miles per hour is kinda REDUNDANT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!duh

Disabling fans and then driving normal speeds is a stupid idea. I would suggest that the fan blades are actually slowing the airspeed. Moving or not, they are in the way!!!
Take them out completely and then shut the engine down when stopped or moving slowly. (ultimate logic)

30 years ago I worked on a Cosworth Vega setup for SCCA racing that did NOT have a radiator fan. A customer walked up and noted that the radiator fan was missing. I told him it was not needed. He asked "what if you are stopped or going slow?" I said SHUT IT DOWN, YOU LOST THE RACE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

bob
 
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