View Full Version : TR2/3/3A Think I'll add a fan on TR3 before I need it. Am I being overly cautious?

04-05-2013, 10:37 AM
I've not had my TR3 in the peak of a Florida summer. I expect to be idling in traffic occaisionally. Haven't had a problem yet, but from what I read, I anticipate the possibility.
PO installed a new core 7 years ago ( 3000 miles). No crank hole. 4# cap. I haven't verified the thermostat.
I'm running negative ground and a generator. I'll install a simple on/off switch... no thermal switch.
From what I've read the Hayden 12" pusher looks to be my first choice.
What are your thoughts on this?


04-05-2013, 11:35 AM

I think a fan, properly installed, is a good idea. I'd install a thermal switch and an on/off switch, and use a pusher fan. Chances are that with a radiator in good condition, proper coolant, and proper thermostat, you will rarely need a fan, if ever, but it's a good idea to have one if you are in a warm climate. Also, after you park the car, the thermal switch will turn the fan on to cool the radiator as long as you haven't disabled the battery.

04-05-2013, 12:46 PM
If you're going to try to survive with the stock generator, then I would recommend using a controller of some sort. I used to run a manual switch and I was always forgetting to turn it off (or on). The generator won't keep up with the fan unless the engine is turning fairly fast, especially if you have the lights on.

04-05-2013, 01:11 PM
I know engine temps will rise when you shut the engine off (no coolant circulation). But wouldn't running the fan in that situation simply cool the radiator and not the motor?
Randall, my thinking was that by using a manual switch, I could choose which accessories to use with the fan. I have my light bar and radio wired through led lighted toggles and I'm in the habit of checking them. Even with my CRS.
What about size? Does 12" seem adequate. (I'm talking about the fan here)

04-05-2013, 02:04 PM
What about size? Does 12" seem adequate. (I'm talking about the fan here)

12" is about as big as you can attach to the TR3 radiator. Of course, there are 12" fans, and then there are 12" fans. When I went to replace the inadequate 10" fan on my TR3 (I have no engine driven fan), I ran into a lot 12" fans with wildly differing cfm outputs. I settled on one that puts out about 1600 cfm, which is quite a bit. I only found one 12" fan that put out more, but the amperage draw was more then I wanted to deal with. As it is, the Spal fan I bought draws about 15 amps while running.

Below is a pic of the 12" Spal that I installed, and the 10" unknown that I took off.

04-05-2013, 04:09 PM
I'm running the 12" Hayden as a puller (which is only rated 800 cfm in free air but also only draws about 9 amps) without a mechanical fan and it works fine for me even in prolonged stop and go traffic in 100F heat. The gauge did creep up a little when it was 115F in Palm Springs a few years back, but the car still took the heat better than the driver did!

My current controller only runs the fan when the water coming back from the radiator gets over 190F. Typically when sitting still, it will run the fan for 40-60 seconds and then shut it off for 20-40 seconds; which reduces the average current draw. The stock generator on a TR3 is only rated 19 amps and even that isn't until the engine is running pretty fast. Subtract 12 amps or so for the headlights plus a couple for the ignition and there just isn't much left to run the fan.

Personally, I really like not having to worry about turning the fan on & off; one of those "Why didn't I do this sooner" moments. But obviously it's your choice.

Next time around, I plan to try building a PWM controller (so the fan runs slower when full cooling isn't required, reducing average current draw even more) and add a function to run the fan when the carb bowls get too hot even if the key is off. But at the rate I've been moving lately, it will probably be another decade before I get that done :)

04-05-2013, 04:50 PM
Good info. My reasoning for the manual switch is that I don't want to pop a fuse if my lights are on. One of these days I'll put in an alternator.

04-05-2013, 08:32 PM
Good info. My reasoning for the manual switch is that I don't want to pop a fuse if my lights are on.
You lost me there. How is having a manual switch going to prevent popping a fuse? Especially when the lights don't even have a fuse.

04-06-2013, 11:04 AM
I've added fuses to my lights, driving lights, and radio. Haven't really thought about where to tap in the fan. I was just thinking that "something" in the system would be overloaded if my amp draw exceeds the generator output? Somethings gotta give, if not a fuse, what?
And my thoughts were that having a manual switch would assure me that the fan would not come on (automatically) if I had the lights on.

04-06-2013, 02:29 PM
Ah, I see. No, nothing will be "overloaded" when the load exceeds the generator output; the battery makes up the difference and all you see is discharge indicated on the ammeter. This is quite normal, even for a car that has not been modified in any way, since the generator produces nearly nothing at idle.

The problem is that the battery only holds so much, so there is a limit on how long it can go on supplying the difference and still be able to start the engine in the morning. As a very rough estimate, a fully charged and nearly new battery should be able to supply 20 amps for about an hour and still be able to start the car (if the weather isn't too cold, etc). But the battery capacity drops off as it ages, so this may be overly optimistic if your battery is near the end of its life or the weather is cold.

Around here, driving at night without headlights is apt to get you pulled over, if not an actual ticket. I'll flip them off if I'm going to be stopped for awhile (like a railroad crossing) but for the most part, I want to be certain that the other drivers have no excuse not to see me.

PS, I don't know what you have now, but I would suggest giving the fan its own fuse, fed in some fashion from the brown/blue (NU) circuit. I mounted a 4-fuse Lucas fuse box next to the original control box and wired it into the A1 terminal on the control box.

04-06-2013, 03:06 PM
Randall, you continue to enlighten me... thanks. I like the idea of a fuse box, neater than inlines. And I have to laugh, I didn't plan to drive without lights. I used to as a kid, but I lived in the country. Here in Sarasota they frown on that.

04-07-2013, 06:33 PM
Even when the water is not being circulated, heat still radiates from hot (the water in the block) to cooler (the water in the radiator). That is why you might want the fan on after shutdown. Bob

04-07-2013, 08:56 PM
Of course you could something easy , cheap, and effective.Simply take off the old paddle fan,
cut off the blades, smooth up the stumps and bolt on a tr7 fan.It is the perfect size and has 13 blades.
The issue with the old tr radiator is getting air to go through the thick core.This trick fixes every thing, and
works in the worst heat you can stand to drive in.
Electric fans can fail, switches burn up, generators overload.Why tax an already marginal system???
MD( mad dog)

04-08-2013, 08:15 AM
Electric fans can fail, switches burn up, generators overload.Why tax an already marginal system???
MD( mad dog)

Modern electric fans are very reliable. Just about all the cars made in the last twenty or so years use them exclusively. Using a relay to control the fan will ensure that you don't burn up any switches, and the marginal generating system can be overcome by installing an alternator.

It's fine if you don't really want to deal with an electric fan, but if you do, a few precautions such as relays, fuses and adequate wiring and charging rates will assure you that all will function well over the long haul.