Poly 313/318 Aluminium Radiator
 

As the revision of my 408‘s Poly 313 is nearing its end I‘m considering whether it‘s a smart idea to change to an Aluminium Radiator. Does anybody have experience with Aluminium rads on these engines?

Your help is much appreciated.

Justin

I considered installing an aluminium radiator when I added air conditioning to my 410 earlier this year but decided to have an uprated core installed in the original radiator. I changed to a pair of off the shelf 11" Spal puller fans in a shroud. One fan is set to come on at about 88 degrees C or when the air conditioning is switched on. The second is set to about 95 degrees. Both fans come on with manual control.

Even during the hot spells this Summer I don't think the second fan has switched on so, for me at least, the original radiator with a new core works well.

Unless you are considering fitting air conditioning you may not need to uprate the fans. This modification isn't without consequence. My new fans draw way more than the existing alternator and wiring could supply. Adding a second fan relay and rewiring the manual switch to operate the relays rather than supplying full current sorted the wiring issue. The higher output alternator needed a new, larger, cable run directly to the battery and rendered the ammeter pointless. Change to a voltmeter per 411 is the obvious fix.

Other points to ponder:

If the block is silted up you may need better cooling to compensate.

Higher output water pumps are readily available for these engines. I bought one expecting to need it but found the existing perfectly adequate, but I'm not certain what is currently fitted.

If you decide to go for aluminium you will have the choice of vertical flow per the original or cross flow, which many seem to advocate. I'm no expert so you will need to research.

You have a choice of built in transmission cooler or fitting an external unit. I prefer internal as it gets the transmission oil up to temperature quicker.

Dear David,

thanks a lot for your very on point description of the possible solutions. This is most helpful.

The water pump and radiator core were already replaced before I started disassembling the engine, which led me to the initial thought of the radiator not being capable enough.

Since you mentioned the change from pusher to puller fans the old pusher units are my prime suspects. The fans turn suspiciously slow. When I got the car the wiring was in quite a sorry state with a negative earth conversion running a lot of things backwards, this including the fans which avoided airflow at all.

I'll run through the cables again. If they are fine I'll also consider changing to puller units. If I change them, would you mind if I consult you for some more details on your conversion?

Have a great weekend,

Justus

I still have the fans and shroud that I took off my 410 if you would like to compare with what you have. Otherwise happy to share details of Spal unit and wiring.

Justin I have a 411 Mk 2 Bristol which years ago I purchased. It was always having overheating and starting problems(when hot). In Australia we get a lot of very hot summer days when the car was almost impossible to drive for fear of boiling. I now have a car that runs cool even in the most severe conditions.I took the following steps
1/ I replaced the inlet manifold with an aluminium aftermarket unit
2/ A new high performance waterpump was installed
3/ I recored the radiator with a modern core 30 % more efficient
4/ High flow thermostat

This all helped but still not solving the problem so I finally followed the advice of my radiator man who told me to replace the 2 Bristol supplied fans which block much of the airflow to the radiator with 2 larger fans which he insisted be installed on the engine side of the radiator that way the full face of the radiator has air flowing through it .

Now the car runs cool on the hotest of Australian conditions.

Justin,
I concur with David and Peter. I don't believe an aluminium radiator is needed. A modern re-core of your existing rad and puller fans (or one big one) mounted on the rear of the radiator should be sufficient.

I did away with the original fan(s) and cowl - not sure if the 408 has two fans like the later V8s. The inefficiency of that design was pointed out to me when I was trying to improve the cooling on my 411 after adding air conditioning.

After a rad re-core and adding a puller fan (or two), without air conditioning (so no condenser in front of the rad) you may get away with leaving the original cowl and fans in place if you want to maintain the original look.

Regards,
Kevin

Peter's post has reinforced my opinion that the fan shroud is the important item here. The unit I bought is still available on Ebay:

https://www.ebay.co.uk/itm/253887160435

I wouldn't have achieved a better fit on the radiator if I had supplied the radiator for a custom shroud. It was spot on off the shelf. The 12 rectangles above and below the fans are rubber flaps that allow air through when driving along and shut when stationary.
The disadvantages of this unit are noise and huge current draw. As my experience during a hot UK summer suggests a single 11" fan running out of the pair has been adequate I wonder whether running both at a slower speed would be a better solution, but I don't think I am likely to find time to try that any time soon.
Another question is whether straight bladed or curved bladed fans are the better option. I just found this from an Australian fan manufacturer:
https://daviescraig.com.au/blog/stra...xVBoUKQBREwjEC

David the 411 fans I replaced the Bristol one were a pair and I managed to get a shroud off an Australian made Ford Falcon which covered the radiator all most completely. Wether you have one large fan or 2 smaller ones depends on the shape of your radiator but the most important point I made is is you want a great result put the fan or fans on the back of the radiator ( ie between the radiator and the motor).

Craig Davis are a highly respected company in Australia

Regards Peter Dowdle

Dear David, Kevin and Peter,

I can't thank you guys enough for all your advice. I'll definitely try to go with the puller unit David suggested and leave the old radiator in the car for now.

May I ask if your cars are also equipped with a skid plate? As you can see on the picture the plate on mine looks to somewhat belong there but it really encloses the lower section of the radiator completely.

Since you've shared your experiences I really start to understand the tricky airflow situation at the front of the car which I never considered as the grille looks so chunky.

I'd be very glad if you guys allow me to rely on your experience again, when the engine is finally getting back in the car and all theory will need to be put to practice.

Regards

Justin

I put the plate back on my car last year after many years without but haven't got around to putting it back on since I fitted the re-cored radiator. Fair to say that it isn't vital for keeping my engine cool. I will put it back on the car and see if I notice any difference.

If you are using the same fans as I did please make sure that you fit a high output alternator ( around 95A) and wire it directly to the battery. Also rewire the fan override switch to operate the relay and not supply full current to the fans per original wiring. Make sure each fan has its own relay and fuse and that all wiring has a large enough cross section for the current it will carry.

I think the original fans drew about 7 amps each. The new fans draw 25 each!

It is also a good plan to have a controller that switches one fan on before the other, particularly to avoid the huge surge on start up. There are some really good PWM (Pulse width modulation) controllers that start the fans up slowly and speed them up as temperature increases, but check the reviews as reliability seems to be an issue. Also, before rushing to buy the same unit as I did you may want to read up a bit on the benefits of brushless vs brushed motors.

Justin,
That's a serious looking skid plate on your car. It looks a bit new and undamaged, so may be not original (not that it matters in my view).

My 411 S5 has a piece of bare aluminium in the same place - not sure if it is original - probably not. I wouldn't really call it 'skid plate' compared to yours, but it would prevent stones from coming up into the engine bay. Mine doesn't have holes in it like yours does.

I suspect skid plates do play a role in air flow in the engine bay, but the water cooling system would play the biggest part in preventing the engine from overheating. It may also have an aerodynamic role. If I were you, I would keep it in place.

For what it's worth, our old ML Merc has one made of plastic, and my Discovery 3 has one that is like tank armour!

As David did, I also had to upgrade the alternator in my car. And you want to be using relays to switch the power to the new fans!

You could of course increase the performance of the cooling system incrementally. You might add puller fan(s) and find you don't need to do anything else. I suspect the modern puller fans with curved blades are far more effective than the old fans Bristol used.

The other thing I forgot to say is do not feed power switching side of the fan relays with a switched ignition feed as this could fry the ignition switch in seconds and melt the wiring. Use a switched feed for the relay coils to prevent the fans operating when the ignition is off.