URGENT !! Travelling Sydney-Melbourne

I need help people.
radiator blockage or thermo?? Not towing just me and 3 kids + camping gear, nothing on roof racks... problem starts when driving up hills on Highway at about 100/110 temperature starts to climb rapidly to about 3/4 on the gage ( 110 /115deg on Torque app) as sokn as I get a flat run, I can see temp drop to about 95/97deg in a matter of a ouple of minutes...
I meed.a fix and if possible a reputable mechanic. Leaving Sydney today heading to Canberra (1nigh) continuing to Melbourne.
at moment driving at 80 /90kph and temp doesnt move from normal 95deg.

any recommendations how check or fix and a good radiator mechanic would be much appreciated.
cheers in advance.

well i doubt ifthe fan is your issue as these clutch fans do slow up at higher engine rpms, there mainly for slow driving as opposed to highway speeds.
i would start with a radiator flush / clean plus a new thermostate as it could be not opening fully when the engine is warmed up . are you losing any water ? if so try a new radiator cap as well. start with these before any cylinder head testing, $$$

No loss of coolant... my guess is partially blocked radiator and/or thermostat..
what I really really need... is a mechanic who deals.with Navaras around Canberra area as im 200ks before, and ill b heading to Melbourne...
I know its a neesle in a haystack... but thats what makes this Navara Forum special.
cheers again

why don,t you just find a radiator specialist around the area your in or going to and get them to do a full system flush including radiator plus fit a new thermostat. if the coolant has been in the radiator for some time there is a chance that the coolant has jelled up and the only way to flush the radiator is to remove a top or bottom tank from the radiator and have is pressure cleaned by the radiator specialist or failing that you may need to buy a new radiator .

It's the viscous hub. Get the engine nice and warm (90+C coolant temp) and stop the engine, pop the bonnet and try spinning the fan. If it turns easily, that's your problem. It's not the first and won't be the last that's failed - I have a spare here because I am on my third (240,000K). If you drive while watching the temps you can go anywhere without damage - we towed a 2.5T caravan up to Nowendoc (and beyond) with a busted viscous hub (fluid couple, it goes by many names). There's a place on the Central Coast that sells good units at a decent price. I'll have to dig around and find their details. I think it's Bretts Truck Parts but I will make sure of that.

One option:
You can get silicone oil from a Toyota dealer.
That's the stuff that goes inside the fan clutch to drive the fluid couple/viscous hub inside the fan unit.
Pull the fan off, remove the screws holding the clutch unit together and put an extra 2 or 3 little bottles of Toyota silicone oil into the fan. Reassemble.
My d40 had been running a little warm, sitting at 92 odd degrees on a cool day, higher when going up hills.
I bought a new dayco fan clutch recently and pumped an extra two bottles of silicone oil into it.
Now it runs at around 87 degrees and I can hear the fan blowing when I'm going up hills or pushing a bit harder than normal.
Might use a bit more fuel but totally worth it.

I doubt its fan related if it only happens above 100kph. Time for a cooling system flush? Sticky thermostat? Swing past the nearest radiator place you can find on google if you are half way between here and timbucktoo.

I had that experience. At above 95km/h the engine is working fairly hard to keep the car moving through the air. It may be a blockage in the radiator, but the fan clutch is really easy and cheap to check.

arn,t those fan types supposed to slow down at higher engine rpms, if the engine is getting hot at slow beach driving speeds theres more chances that this viscious fan unit is faulty. i would go the radiator clean outplus thermostat replacement.

You'd be surprised how often the cooling problems start with the fan clutch in D40s.
It's why I put more oil in mine, so i could hear the little bastard whirring like in all the other 4wds I've owned

Thanks guys... leaving Canberra now towards Melbourne.. will try to find espe ialiston the way or in mMelbourne and get them to flush cooling system.
as always... all input is much appreciated..
THANKS

Not to sound like a broken record but check the fan clutch too for sure, D40s chew through them

Czechmate said:

Not to sound like a broken record but check the fan clutch too for sure, D40s chew through them

Click to expand...

you don,t need a fan at highway speeds you know, only for low rpm and slow driving, thats the way these clutch fans opperate, higher the rpms the slower the fan spins.

The hotter the air blowing over the fan hub, the harder it should engage. That should include higher rpm. The only thing that governs the speed of the fan is the viscosity of the fluid inside the hub assembly.

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This may be worth a read www.neuralfibre.com/paul/4wd/tuning-and-understanding-your-toyota-viscous-fan-clutch

I know it's for a Toyota, but same principle...

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^ As above, the hotter the engine gets the more the clutch should grab so the faster the fan should turn over. Hotter engine = faster fan = more cooling.

Don't sweat on their fragility. Was reading a post by a Porsche owner who replaced his viscous hub and had it fail just 24 hours later. Same symptoms - at higher speeds (= higher RPM = more combustion per second = more heat developed) his engine started cooking. And his Porsche wasn't the aerodynamic equivalent of a housebrick like our Navaras are.

well there you go, a guy told me years ago that these viscious fans were designed to opperate fast at slow engine rpms and opperate slower at higher engine rpm,s , thats why they got rid of the old style direct fan blade to pulley drive as they caused more un needed drag at higher engine rpms.

If you're at all worried about heat, you want to be able to really hear your clutch fan cranking.
You can put as much silicone oil in there as you like, the only drawback is extra fuel consumption.
A bimetallic strip moves when the engine heats up to open the
oil ports within the viscous drive/fluid couple.
The more oil in there, the more that gets through the ports to drive the fan.
A mate has a 98 td42 patrol with rebuilt heavy-duty engine and a big turbo and intercooler, setup for low-down grunt ( he tows a 2 tonne trailer around the country for work)
He was having heat issues despite a new massive aussie desert cooler radiator.
After I did my clutch fan with extra oil I let him know and he did the same thing, helped out quite a lot.

Seems a bit counter intuitive that it could be fan related at highway speeds. Shirley at 100kph you are getting far more air-flow than a fan could ever supply.

Because the rpm tend to be up at highway speed the fan spins quicker and still helps out a lil bit
Guess having the coolant and block cooler to begin with helps too