Thermo fan bypass

[Junosi]

Here's a few photo's showing how to wire up some bypass switches to your thermo fans. As noted by many people the thermo fans come on way too late on the P38 and by the time they come on you are already running very hot. If you know your temp is climbing you're better off switching the fans on early.

The fans have two speeds - I'll call them low and high speeds. High is quite loud. I turn mine on when I'm doing low range hill climbs and crawling in traffic in middle of hot summer with aircon etc on.

Wiring is easy - there's two connectors located near the lower left corner of the radiator. Both connectors are connected to part of the aircon system. Simply tap into both these (or one or the other if you only want one speed switch). Personally I ran a piece of 5 core trailer wire through the firewall to the area as it's tidier and easier to work with - 2 wires to each connector. I go through the firewall where Ron has suggested in another post (below the radiator expansion tank)


I forget which switch is low speed and which is high...
Photo's were taken with bumper off.

2 wires go to each connector. The connector on the right (photo's right) only has two wires so that's easy. Yellow and brown wires are my switch wires to this switch.
30728

Connector on (photo's) left has four wires - connect to the black and the black/blue wires. Red and green wires are my switch wires to this switch.
30727

Switchs mounted inside the ashtray - ashtray removed and bent bit of aluminium in place. Yellow switch is low speed, red is high speed. Knob is subwoofer control. HEVAC waiting for replacement to arrive ...
30729

That's about it.

edit: One thing to note is that the 'low' speed won't activate unless the aircon is on. High speed works regardless.

[Hoges]

Here's a few photo's showing how to wire up some bypass switches to your thermo fans. As noted by many people the thermo fans come on way too late on the P38 and by the time they come on you are already running very hot. If you know your temp is climbing you're better off switching the fans on early.

The fans have two speeds - I'll call them low and high speeds. High is quite loud. I turn mine on when I'm doing low range hill climbs and crawling in traffic in middle of hot summer with aircon etc on.

Wiring is easy - there's two connectors located near the lower left corner of the radiator. Both connectors are connected to part of the aircon system. Simply tap into both these (or one or the other if you only want one speed switch). Personally I ran a piece of 5 core trailer wire through the firewall to the area as it's tidier and easier to work with - 2 wires to each connector. I go through the firewall where Ron has suggested in another post (below the radiator expansion tank)


I forget which switch is low speed and which is high...
Photo's were taken with bumper off.

2 wires go to each connector. The connector on the right (photo's right) only has two wires so that's easy. Yellow and brown wires are my switch wires to this switch.
30728

Connector on (photo's) left has four wires - connect to the black and the black/blue wires. Red and green wires are my switch wires to this switch.
30727

Switchs mounted inside the ashtray - ashtray removed and bent bit of aluminium in place. Yellow switch is low speed, red is high speed. Knob is subwoofer control. HEVAC waiting for replacement to arrive ...
30729

That's about it.

edit: One thing to note is that the 'low' speed won't activate unless the aircon is on. High speed works regardless.


For several years I had a V6 Calibra (a b-e-a-u-t-i-f-u-l car :p:twisted:) and the thermo fan arrangement was such that when the car was parked on a hot day, the fans kept running to reduce the effects of heat sink...your wiring gives me an idea :eek:...thank you!!! :BigThumb:

[wayneg]

Thanks for the How to, looks very simple. Just wondering if I just make a permanent connection across the 2 wire switch so the fans come on with the aircon will the fans be on low or high speed.

[Junosi]

will the fans be on low or high speed.

If you put the short on the correct switch it will be low speed.

[wayneg]

D.one in 5 mins, easy peasy..... Driving the Holland Track starting tomorrow so extra cooling is there if required

[Keithy P38]

Just looking at this post, does anyone know which of the wires here are for the high speed of the fans? I’m tinkering at the moment and want to play around with manually switching the fans on high speed, but I don’t have access to the wiring diagram. I don’t want to just go cutting wires for the sake of it unless I absolutely have to.

From reading this post, it appears that the fan power supply is normally closed (that is, when the circuit is live the fans are told not to run), but when the earth/negative is removed the fans will be triggered to run.

If you’re super keen to get an idea of why I’m doing it, check out this video series:

Thermofan Installation Series - YouTube (https://youtube.com/playlist?list=PLjuYKRXivJ98HbfpH9BEy5Fn2bs-GxVcV)

Cheers
Keithy

[prelude]

I would have to look that up, don't know from the top of my head. However, I remember your thermofan project. Did you ever revisit your original post on here? I updated it a while back with some power experiments: Thermofan over Viscous? (https://www.aulro.com/afvb/technical-chatter/278182-thermofan-over-viscous-4.html)

Wonder what you are thinking :)

Cheers,
-P

[Keithy P38]

Cheers mate, I did a bit of research playing around with the factory A/C thermo fans yesterday afternoon and worked out that they’re negative switched, and normally open (so applying a negative/earth activates the relays).

Watch this space!

Ill go and re-visit the post now! I completely forgot about it!

Cheers
Keithy

[Keithy P38]

It’s easier to explain the outcome via video than over typing, so here it is!

Operation extra-cool with a TWIST - Can I enlist a helper to back up the Range Rover thermofan? - YouTube (https://youtu.be/wWokW6f3bFU)

Cheers
Keithy

[old dirt bikes]

It’s easier to explain the outcome via video than over typing, so here it is!

Operation extra-cool with a TWIST - Can I enlist a helper to back up the Range Rover thermofan? - YouTube (https://youtu.be/wWokW6f3bFU)

Cheers
Keithy


Hi Keithy, I have looked at your videos and I am having a bit of the same problem. Although mine is a bit of my own doing. I have rebuilt my motor and made it a 5lt with 9.8 to 1 compression ratio. So it generates a fair bit more heat than a standard motor. Also I have fitted aftermarket headers which dump a bit more heat into the engine bay. I have also fitted a Aussie Desert Cooler all alloy Radiator which holds 25 percent more coolant. 37c here the other day and I was out playing in the traffic and the motor got up to 94c. I have the condenser fans wired up to a switch so I turned them on and the temperature stopped rising. Once the traffic got moving the temp went down to the normal 85c. I am going to stay with the engine driven fan, but I will add a bit more viscous fluid to it to get it back to original performance. I am interested in that gauge you put in your dash. What brand is it as I would like to make the thermos come on automatically. I cringed when I saw you drill that hole in your dash. I made and fitted a gauge pod on top of my dash that holds 5 gauges and there are no holes in the dash. A lot of thought went in to that. I will let you know it the extra viscous makes any difference. I am also looking a a bonnet scoop with a rear opening to let some of the hot air out. My background is the last 40 years I have worked in the automotive air conditioning industry, so I have some experience in trying to get air flow and AC to work on vehicles that were not designed for this climate. I did spend a lot of time up your way out at Century mine where the temperature in summer averages 52c and down in the pit can get up to 65c. Air cons work really hard up there.
Regards, Alan Temperley

[Keithy P38]

G’day mate,

I’m feeling your pain re: the drilling into the dash! I didn’t take that one lightly! It came out great though, I’m very glad that I did it. It’s a SAAS thermofan control unit that I got from my local auto parts store.

It sounds like you’ve had a bit of a tinker with yours too, I like what you’ve done keeping the viscous and adding the A/C fans and the bigger radiator. And the bigger displacement interests me too - how does it go with the bigger capacity and compression? I’d imagine pretty well 😁

I regularly visit out west, although I haven’t spent a great deal of time exploring past Cloncurry. It’s beautiful out that way in its own way!

Cheers
Keithy

[old dirt bikes]

Hi Keithy,
yes I agree the gauge in your dash looks good. I bought another P38 just to get a good dash so when I decided to fit some extra gauges I was not going to drill any holes in the dash. So my gauge pod with 5 gauges is fitted without any holes in my dash.
The engine fan when working properly will pull a heap of air. The problem is they are all getting old and have lost some of their efficiency. I am also looking at fitting a bonnet scoop to vent some hot air out the back of the bonnet.
I have only done one decent trip in my P38 since I got it going, and it went really well. Some of the problems with the 4.6 are the low compression, poor camshaft, badly designed cylinder heads, terrible computer fuel and timing maps. Yes just about everything. But it can be improved fairly easierly. It just takes time and money. But I only paid $1,000.00 for the vehicle so I could afford to spend a bit on the motor. And it does go very well. It gets about 11.3 lt per 100k's on a run and 15 to 18 around town, depending on how many V8 Toyota's there are to race from the lights. Having driven a standard P38 for 17 years this one is like a sports car. From a standing start a quick stab on the right pedal and you are doing over 100 kph. I still have a bit to do on my P38 but I am happy with it so far. We are looking at a trip to the cape next year.
From your video's it looks like your steering wheel is getting a bit second hand. Mine was good so I rubbed a lot of leather lube into it and covered it with leather. I also covered the instrument cluster trim and the consol with leather. I have also fitted a wide screen headunit and I replaced the ashtray with a set of rocker switches. I have managed to attach some photos.
Regards,
Alan Temperley



G’day mate,

I’m feeling your pain re: the drilling into the dash! I didn’t take that one lightly! It came out great though, I’m very glad that I did it. It’s a SAAS thermofan control unit that I got from my local auto parts store.

It sounds like you’ve had a bit of a tinker with yours too, I like what you’ve done keeping the viscous and adding the A/C fans and the bigger radiator. And the bigger displacement interests me too - how does it go with the bigger capacity and compression? I’d imagine pretty well 😁

I regularly visit out west, although I haven’t spent a great deal of time exploring past Cloncurry. It’s beautiful out that way in its own way!

Cheers
Keithy

[Keithy P38]

That’s looking and sounding good mate! The fuel consumption is impressive too. I like the way you’ve set up your switches and gauges - very tidy indeed. It definitely sounds like an aftermarket ECU and a good tune would do these things some good.

Yes, the poor steering wheel has copped it bad. The North Queensland sun and living outside permanently at the moment has definitely not helped the situation. I do have a new wheel on the list of things to do.

Cheers
Keithy

[prelude]

with the risk of running this thread completely off topic...

I am contemplating an aftermarket ECU and BECM. Replacing both would make the vehicle much more reliable / repairable in the future for me at least since I am fairly good with electronics so replacing it all with commodity hardware seems the way to go. Personally I am thinking about swapping it all out for arduino's since they are a dime a dozen, available everywhere and there is huge support.

The BECM would be replaced by an arduino with a large extension board for all the in/outputs I would need and the ECU with a speeduino. Keeping the base computer the same seems like a good idea.

Back on the heat topic: I am not sure I would want a bonnet scoop. Those side vents like the L322 would be my first choice from an aesthetic point of view, if they would work sufficiently that is.

Cheers,
-P