Overheating GU 4.2TD

Goldfinder,
I recently replied to someone on the Patrol forum with regards to this, see below:

The 4.2 Diesel GU Patrol has two switches on the bottom radiator tank.

The one at one end switches on the electric fan (in front of the radiator) when the temperature on the bottom radiator tank is getting too hot few degrees higher than normal.
The one on the other side switches the A/C compressor off a few degrees higher again to releave some of the heat load because while the A/C is going the radiator is getting hot air from the condenser.
In other words, if the radiator is not coping the fan starts first, if that is not enough then the a/c compressor is cut out to give priority to the engine cooling instead of the passenger's comfort.
In the 3.0L and the 4.8 that is all controlled by the ECU, hence no switches at the bottom of the radiator. In fact the fan has two speeds and through the ECU the 3.0L model switches the fan at low RPM and then higher when needed.

IF you look carefully you will find that the shroud is split with one side having straight through square ducts, the viscous fan cannot cool down that area of the radiator so on a hill at high revs and low road speed the radiator size is reduced to 80% because the fan drawing most of the air cannot draw through those ducts (air filter side), that is when the electric fan cuts in and cools that side and gets 100% air flow for cooling .

In my opinion the radiator is too wide and too short (that is probably why the new 4.2TDI has a different radiator, narrow and long).

I never had any problems with mine only once on a very hot day in first low in the high country the a/c cut out, however recently the a/c cut out flogging it up a hill so I decided to clean the radiator fins etc (as suggested by Bazzle several times) and I found it all blocked with dust, leaves and feathers from an emu I hit near Tibooburra.
The process involved removing the radiator, blowing it through with air "while still dry" and then washing it up and blowing it again.

To check it, it is quite simple, when you remove the radiator it may look OK (not dirty) but you must be able to "see through" the fins, the areas you can't see through are blocked to air flow.

The reason why it should be done "dry" blowing with air is because insects, grass and seeds swell when you wet them and then you can't remove them.

The GU radiator is a single row type all alloy and the fins have slots in them which catches those little black night insects, the dust then gets cought behind the insects and the blocking process starts.

It took me all afternoon of blowing air and I still could not get 100% of the insects out but I could see through (by the way I have always had a mesh since new) but these insects fit through the mesh and the A/C condenser.

I took the chance to change all radiator hoses at the same time and all belts.

While I was at it I blew the a/c condenser through as well.

I have tested it since and it is fine.

Also make sure the viscous fan cuts in, I can hear mine roar as soon as there is a hill or the outside temperature is high.

I believe the overheating problems everyone reports on 4.2 engines are a combination of three things:

1) Cast iron head indirect injection (combustion in those engines happen further in the head than in a direct injection and it is designed to heat the air on compression) and cast iron does not get rid of heat quickly (Just the reason why camp ovens are so good for cooking).

2)Engine design, water jackets too small and slow flowing designed for low engine speeds.

3) Radiator too short/small with shrouds not designed for good air flow at low road speeds.

Taking into account the first two points while driving should keep you safe, lower RPM and lift throttle when the going gets tough, the 4.2 will still pull at 1500 rpm...

I first knew there was a heating issue with these engines when while driving mine new up a hill on freezing temperatures outside -5 the viscous coupling fan engaged and roared all the way up hill... If it did that while on -5 degree temps what hope do they have of cooling efficiently if the outside temperature is 45 degrees and you are towing a heavy trailer??

Will

The best solution that I've seen for GU 4.2's and some 3.0's is to remove the viscous fan all together, instead fitting two large thermofans in it's place.

This allows N+1 redundancy and high flow rates around the airconditioning condensor (supplied with it's own fan) and exchanger core.

My 3.0TDi has two Davis-Craig DSL16's, one configured for pulling, the other for pushing the air. This allows you to dispense with that STUPID plastic shroud and effectively cool the whole engine.

My question to you is; Have you changed anything on the front of the truck? For example, Large bullbar, driving lights or fly-screens? Anything that would reduce airflow? If you are using the standard Aluminium Nissan bullbar, have you taken off the plasic shroud at it's base?

If you have, then try testing the effective airflow under the bonnet, in front of the grille by using an airflow meter of some description. I bought a Tandy unit for this purpose. It has two output pins for the tacho, that you plug into a multimeter, set to tacho.

If all else fails, you can "up rate" your exchanger, but this will cost heaps of money and potentially ruin your warranty claims status. SImilar to what I've done with fitting thermo fans!

Another thing about Thermo's.. They don't like swimming that much. I tend to put a blind over the front of the car if fording more than 500mm. I've also designed a small PIC-based computer that runs the thermo fans on for up to 10 minutes after engine switchoff, to cool water/engine on hot days. As you would know, engine temps actually RISE after you shutdown, as the cooling system is not powered.

Regards,

Chris Ford.

Thanks for the replies. Most of my problems occur at speed usually when towing at 90kmh plus so airflow at these speeds should be pretty good. To get the aircond to come back on I have to slow down to a very slow pace for a good 5-10 mins to allow the motor to cool. I do have a steel bullbar as fitted by nissan. I am willing to spend money to rectify this problem on an otherwise great car. Possibly an aftermarket manufactured larger rad. I will give the thermo's some thought as well.

goldfinger.
Just a bit of engineering data to help you understand the problem. A motor is about 15% efficient, alowing for the heat out of the exhaust we can assume about 80% of the remianing heat goes out through the radiator, so if you are driving flat out you are producing 100kw from the motor that means 500kw is going into the radiator. I dont know if you have any way of comprehending that amount of heat but that is more than you use to heat a small shoping centre. So to solve the problem you must let the hot air get away from the engine compartment, the plastic sheet that is used to stop the mud from the front wheels getting onto the motor is a major restriction. another aproach would be to move the fan forward and then cut the cowling down to allow more air flow. This increases the risk of damage to the radiator in a minor collision. The hot air flowing agianst the fire wall and coming into the plenum chamber is what is over taxing you air con. Eric.

I fitted a DTS exhaust with a new turbo elbow. It has much less restriction and lets the heat out faster, and gives you about 15% more power.
Another idea is to put a slightly 1-2 degree lower thermostat in the engine, so it opens earlier, and lets the coolant cool down earlier.
Other than that, take as much un-needed junk out of the caravan and lighten your towing load.

Thanks all for the helpfull advice and I will take all answers into account to try and solve the problem but the bottom line is that a $60K vehicle with a rated towing capacity of 1300kg (I think?) and my van loaded would not be that heavy (jayco Hawk offroad Camper) should not have an underated cooling system. One for Nissan to solve!!

Cheers!!

Roachie I have never heard my fan come on in the Patrol or any other vehicle I have owned with a viscous coupling.