Do you really need 2 radiators

Hi all,
A question to get some debate going.
Are the two radiators on the 1997 Super Custom 1kz-te really necessary ? I am aware that some of the early Toyota Hilux Surf 1kz came out with the 2 radiator setup but when it moved into the later Hilux and Prado only one radiator was used. I am wondering if it is possible to do away with the bottom radiator and replace with a good quality 3 core.
I thought it might be something to do with the dual a/c but looking under a Hiace Commuter with dual a/c it doesn’t have the 2 rads but has the a/c condenser horizontal.
Has anyone had any experience or thoughts on this ??

The 1kz-te has an awful cooling system as stock which I think is one reason they fitted the 2nd rad. I've done an extensive post on this subject and how to fix it if you search.

Basically there are two issues:
1. The engine (and main rad) is out of the natural airflow in the middle of the van.
2. The thermostat is one of these '1990s trendy' inlet thermostats that cost many car firms (inc. Porsche which had the most famous failures of the 996 and 997 engines) €millions and ate a hundreds/thousands of engines.

In cold weather the 2nd radiator would actually pose more risk to the cylinder head IMO as it is a reservoir of cold coolant.

The system is thus:
1. The thermostat is on the inlet side of the coolant flow.
2. There is a water channel from the head to the rear side of it to cause it to open.
3. The temperature gauge is sabotaged at the factory to ignore the resultant wild temperature fluctuations in winter (it self centres when powered up and is dragged up or down by the temperature sensor resistor, and they added a zener diode in the gauge to hide all movement in the middle range from the driver.
This has the side-effect than an overheat is very difficult to spot and generally cracks the head.

I can only suppose the system was introduced to the motoring industry by a professor who didn't understand the implications, I think it's designed for faster warmup to save fuel.
The problem with this system is that it takes a democratic vote between the head temperature and the radiator temperature, and that vote is decided by a very slow, unresponsive wax car thermostat. This allows (has been measured on a Lotus) the head temperature to get much too hot and much too cold, sometimes several times in the same journey.

When cold it allows huge slugs of freezing coolant into the engine as the thermostat slowly closes, causing wild thermal oscillations, causing head expansion and contraction which cracks heads (1kz) and if the head is stronger takes out the head gaskets (landrover, lotus, Porsche).
Interestingly all radio oscillators rely on a delay in the circuits - in this circuit it's the thermostat itself. They unwittingly built an oscillator.

When hot after a run and idling at traffic lights the radiator water temperature is fine so the democratic cooling to the engine slows which allows the head and bores to get super hot. Porsche added into the mix poor cylinder cooling flow so their open-deck bores turned into soft cheese at the lights. Then when you set-off from the lights the acceleration adds to the heat load and the (Porsche) cheese bores scored and some failed entirely (D-shaped chunks fell off, the coolant rushses in).
The 1kz-te in hot climates didn't have the Porsche issue with bores as the block is very strong, instead the head just cracks instead.

The bodge fix is to fit a lower temperature thermostat, which obviously helps the issue but costs in MPG on a diesel, which isn't great in a sturdy 3 litre van anyway. This is used in many older Porsche repairs now (ref. Hartech).
The correct fix is the Landrover solution and their remote high-bypass pressure sensitive thermostat, and an fixing of the temperature gauge.
I did this one and in use the engine warms up nicely and the needle hardly moves, just up about 1mm on a hill. My view about this is that the Landrover are a lot smarter than the people who designed the Toyota, Rover and Porsche motors.

So would I remove the 2nd radiator in my fixed system? In the UK without towing I probably could, but it will reduce the absolute cooling limit so I think it would depend where I lived. In a hot country or if I was towing or carry big loads - probably not.

BTW there is a BMW diesel engine that has this system as well, but the motor is so efficient that the only symptom is that the in-car heating stops working. That engine would do well in a Hiace, it's in some of the old Rovers IIRC and would make a good transplant !

GPW, thanks I knew I could count on you for a reply. I am in the process of rebuilding my 1997 Super Custom 4wd 1kz-te. I have rebuilt all of the front and rear suspension and brakes, bushes. During my many many hours spent underneath it over the last weeks I have been thinking about the inherent overheating issues. The engine and cooling system are my next part of the rebuild.

I have new belts, 76 degree thermostat, hoses, temp gauge, egt gauge. It has a new main rad but needs flushing and new coolant.

I will reread your previous posts re cooling but living in Australia I don’t want to be having constant overheating issues.

Australia, I forgot to look where you were LOL. Yes, I'd keep the rad!

I did two threads you may find useful:

1. Removing the 'damping' on the temperature gauge so you can see the small changes
https://hiace-super-custom.forumotion.com/t3426-modding-the-toyota-temperature-gauge-no-zener-dead-zone
2. Putting in the Landrover high-bypass thermostat
https://hiace-super-custom.forumotion.com/t3430-cooling-the-1kz-te-in-the-hiace-super-custom

If you are rebuilding it anyway I'd definitely go for mod 2. By the time you eventually get to the old thermostat you'll be sorely tempted anyway, I remember thinking 'They put it where ???'

The Landrover thermostat mod also evens out the head cooling BTW: Usually the only flow out of the head is into the small internal bypass down to the thermostat, the left hand route to the radiators being blocked off (by the inlet thermostat). Then whenever the thermostat is open the bypass gets blocked and the water rushes out of the left hand side into the radiators instead.
With the Landrover part the water always flows at full speed out of the left side of the head (and some through the bypass - depends on your dummy thermostat arrangement, trying to recall what I did), and the flow is diverted on the post radiator side by the Landrover part to either take it from the bypass (hot), radiator (cool) or a mixture. Then it travels into the engine while it mixes in the pipe.

So the Landrover part works just like a thermostatic mixer in a shower (the engine in the position of the person having the shower, the 'hot' side from the head (via a big T piece to the radiator) into the big bypass pipe, the 'cold' from the radiator outlet).
The pressure sensitive part causes it to favour the cold path at high flow rates which pre-empts the need for extra cooling which is neat too as it reduced heat spikes.