TR2/3/3A Electric fan wiring

[GTP1960]

One of my winter projects is to install a electric pusher fan on my 3A.
i have the 12" fan, but I am wondering what is the best way to wire it ?
& are there pre-made harnesses available.

i am thinking I want it thermostatically controlled, but with a dash override-switch.
(I have heard the fan can continue to run long after engine shut down, draining the battery)

suggestions appreciated!

thx

Guy

 

[Geo Hahn]

the wiring is usually so straight forward that ready-made harnesses aren't needed.

the simplest way I found was to switch the ground side. you will want it fused and some use a relay.

I like a dash over-ride, but not one that shuts the fan off. what happens if you forget you over-rode it to be always off?

I actually changed the wiring on my british car with a stock electric to let it continue to run after shut-down. helpful for brief stops such as fill-ups on road trips.

I do have an override but that is to force the fan on irrespective of temps. sometimes it is a hot day and you are at the beginning of a 6,000' run up a mountain road and figure 'why wait for the fan to kick on?'.

another useful feature is an indicator light that tells you the fan is running.

I do recall there are some wiring digrams in the archives.

 

[TR3driver]

If you don't want the fan to be able to run with the key off, then you'll need a relay to control it. Probably the easiest way to go would be one of the aftermarket fan controller kits, like the DeRale

https://www.jegs.com/i/Derale/259/16759/10002/-1?parentProductId=758411#moreDetails

It includes an "air conditioning" input that you can wire to a dash switch instead, if you want.

I see they now have a PWM kit, which might be interesting. https://derale.com/products/electri...oller/pwm-fan-controller-push-in-probe-detail
The advantage of the PWM would be lower current consumption most of the time. The stock TR3 generator (even if you have the later 22 amp model) has a hard time keeping up with fan & headlights at the same time; especially in rush hour traffic.

Based on my own experience, though, I would advise against having a dash switch to disable the fan. I ran for some time with only a dash switch to control the fan, and I can't count how many times I forgot to turn it on. Kind of embarrassing, sitting at a traffic light thinking of something entirely different, and noticing the steam rising from the overflow Even if you don't opt for having the ignition control the fan, it shouldn't run for very long as long as the sensor is located where the fan can cool it with the engine stopped.

I "rolled my own" fan controller; and for my next version I intend to include both PWM and a timer to run the fan for a limited time after the key is off. I'm hoping that will make the car even easier to start when hot. The ARE heat shield helped a lot, but it can still take some cranking to get it fired up when it's only been off for a few minutes on a hot day.

 

[TR3TR6]

I installed an thermostatic controlled electric fan on my TR3A. I also installed a manual cut off switch under the dash. I just got into the habit of checking the manual switch to make sure it is on before I start the car. I have let the fan run after shutting off the car, and like Randall said, it doesn't run that long. What I have found is that unless it's a pretty warm day, the fan doesn't even come on unless I'm sitting at a stop light.

 

[Geo Hahn]

a consideration in all of the above is whether this electric will be your only fan or just be employed as a helper fan in addition to the stock crank-mounted fan.

if the latter, then that begs the question of why the stock fan isn't enough.

there are many reasons for adding an electric fan -- some better than others.

 

[TR3driver]

there are many reasons for adding an electric fan -- some better than others.

I agree; but in my opinion cooling systems in the 50's were simply not as robust and oversized as we have come to expect today. I was reminded of that last weekend, while I was explaining to the wife why there were signs for "radiator water" on Grapevine Hill (I-5 leading up to Tejon pass). Back then, we simply expected that cars would sometimes overheat under extreme conditions. I can remember taking road trips with the family : When we pulled into a rest stop, many of the parking places would have little puddles of coolant where cars had lost some of their coolant during "heat soak".

If you are having persistent overheating problems, especially while cruising at constant speed, then there is something wrong that really should be addressed. Such problems are common on old cars (not just Triumphs) and can be a wide variety of things. Just adding an electric fan is not a good way to deal with such things: it probably won't work and the underlying problem may lead to disaster. My first TR engine rebuild was after Dad's TR3A swallowed a valve, caused by lean mixture and high EGT. Dad said it looked "like a cloud of engine parts chasing me down the road".

But if it is just a matter of the gauge "creeping up" in traffic then an additional electric fan is a good solution. Lots of folks (including you as I recall, Geo) use bigger mechanical fans and/or other changes (like a scoop to direct more air into the radiator). But the nice thing about electric is that it only sucks power (and fuel) when it is needed. Those oversize mechanical fans take power to turn, even when they aren't.

 

[poolboy]

I would recommend a switch in the cockpit that can turn the fan on in advance of the thermostatic sensor.
If you anticipate a situation that you know is going to activate the fan, you can use that switch to get a head start on the situation.
I wouldn't see the need for the switch to turn the fan off IF the sensor says it needs to be on though.
You might check out what "Northcoast Performance" has listed on ebay..They have some nice package deals, just read the description and don't rely solely on the picture.

 

[TR3driver]

FWIW, I use only an electric fan on my TR3, with a controller I built myself (mostly from junk box parts). I installed a dash switch as a backup in case the controller fails; but I've never had reason to use it. The fan almost never runs, except at stop lights or stop-n-go traffic. Then it comes on, runs for a minute or less, and shuts off again. The needle on the temp gauge never quite gets above the '5' in 185 (and my thermostat doesn't open until it touches the '8'). Now I do have a few other cooling improvements (no crank hole, recovery bottle, 10 psi cap) so yours may not work as well. But there shouldn't be any need to turn the fan on "in advance".

 

[jfarris]

Guy,
On my TR6, I used a Northcoast Performance fan (on Poolboy's recommendation) with a Derale relay kit. I put a "turn on" switch on the dash that had a lighted end showing when the fan was being powered. I did have to put a diode in the line as the fan spun in the wind and acted as a generator illuminating the light all the time. I was very satisfied with the install and outcome. I haven't had any overheating problems with my TR3.

 

[GTP1960]

a consideration in all of the above is whether this electric will be your only fan or just be employed as a helper fan in addition to the stock crank-mounted fan.

if the latter, then that begs the question of why the stock fan isn't enough.

there are many reasons for adding an electric fan -- some better than others.

My short saga of going with an electric fan, ends with Murphy's law:
running hot & couldn't figure out, or pin point why.
Since I am planning to go with a narrow belt conversion & an alternator anyway; I added everything else (under the apron) on the menu:
GT6 yellow 8 blade fan
Chinese aluminum radiator (pre configured with pusher)
6 blade water pump
bellows thermostat
evans waterless coolant

after i purchased all this stuff; my mechanic points out my motor mounts are worn out & crushed: the engine is sitting a couple of inches to low and causing a kink in the upper radiator hose........and that was my problem.

murphy's law

 

[TexasKnucklehead]

I have an electric fan added because I live in Houston, and it gets real hot, and we have terrible traffic. The mechanical fan was replaced with the backwards yellow plastic fan. I do not have an override switch to enable (or disable) the fan. I purchased the cheapest Hayden controller they had at the local auto parts store because it included a relay and temperature probe that sticks into the radiator and some wire -and no adjustments. (I have the probe stuck into the top but it could be stuck into the bottom to turn on sooner.) I have it wired to only run when the key is on (and above the temperature/probe set point), and I still have the starter crank hole in my radiator. The fan is mounted just above the hole. -Not all fans are created equal. Some have curved blades, and some take a lot more power to run than others (but cool better/faster). I have a cheap fan, with flat blades that doesn't take too much power so my generator can keep up -mostly because it rarely needs to run.

I have not overheated in my TR3. -even when stuck in traffic during the repaving of I-10 at night between El Paso and Tuscon with the outside temperature barely under 100. Like Randall, I have seen old signs indicating that cooling systems have changed. My favorite is "turn off A/C to avoid overheating on hill". -seems like an oxymoron to me.

I would like a light to indicate the fan is running. But, usually, it is only running when I am in stop/go traffic and I can easily hear it turn on and off. I like to pull the choke cable a little so the idle increases to the point the generator is keeping the ammeter on the plus side. I am much more comfortable knowing I have an aux fan.

 

[GTP1960]

Thanks fella's!

i appreciate the input ; your a BIG help.
i went with that harness Randall mentioned (wiring is not my strong suite), but I'm going to find one of those lighted switch, to assist my old memory, and hook it up to activate as needed.

Texasknuckle: Columbia, SC is about the same size as Houston was back in the late '60's ( when I lived there) , but we have already mastered the traffic jam over here.

On the other hand, if I head off to the west on state hwys. , in 5 minutes it's just me and the road, and the countryside.

thx again.