Strange overheating

[Hobs]

So its an odd one. Basically if i go 100 km/h +. I over heat so turning the heater on brings it back to normal. It will never overheat in trafic with the aircon on even with a banket blocking the front grill.
Highway hills seem to trigger it. If i take em at 80. No probs.
Any ideas. Thanks ?

 

[Old.Tony]

Almost sounds like the thermostat isn't opening all the way, or the water pump isn't working as well as it should.

I'd firstly check (because this is the cheapest thing to do) that there's nothing blocking the radiator core - mud is the biggest culprit, but plastic shopping bags also cause dramas.

It might be an idea to make sure the belt isn't slipping too. The last free thing to check is the fluid drive in the fan. Get the engine nice and hot, then turn it off, open the bonnet and move the fan - it should be very stiff. If it's easy to turn, that's the culprit.

If that's good, get the thermostat looked at.

 

[scooba_285]

i agree with tony, cheap the cheap things first and go from there

 

[Hobs]

Thanks. Ill test the fan. I have looked for the thermostat before, removed the housing where i thought it should be and there was nothing there. Im up over 200 000 kms so ill replace the water pump as a precaution.

 

[nathand22]

is it using any water at all??

 

[Hobs]

Doesnt lose a drop. Ill test the fan today and force it to over heat and see what happens

 

[Hobs]

Ok. Couldnt get it to overheat ( double demerits and all ) but at normal running temp the fan spins rellatively easily. Maybe about 100 grams of force at the tip of the blades.

 

[Krankin]

how old is the truck and is/has the coolant been kept up to standard?

is there any engine mods?

diesel or petrol?

 

[Hobs]

5 years old done just over 200 000 ks. The problem started about 2 years ago so recently its been neglected as a work ute. So i know from driving larger deisels especially cummins engines the temp goes up and down but not like this ute. My navara has never gotten into the red because i turn aircon off and the heater on.
In the first few years i did all the way to coberpedi with the aircon blasting no problems. Temperature didnt go above half. Now sydney to wolongong makes me uncomfortable.
Theres no mods its a stock str 3 diesle.
By the way ive been reading about bypassing the polution gear. But visually the turbo seems to not have a built in waste gate. My truck breathes a little heavy too so i think a catch can should be put in.

 

[amber.2]

I have a similar problem i can drive around for weeks on city freeways at 110kph but as soon as i head down the Hume highway toward Bowral from Cambelltown the temperature goes up, it could be because its a gradual climb all the way it gets to about 80% on the guage ive changed the thermostat and the cap coolant was changed about 2 years ago,
On the way back it sits in the middle of the guage, could be the radiator needs a flush?

 

[Krankin]

5 years old done just over 200 000 ks. The problem started about 2 years ago so recently its been neglected as a work ute. So i know from driving larger deisels especially cummins engines the temp goes up and down but not like this ute. My navara has never gotten into the red because i turn aircon off and the heater on.
In the first few years i did all the way to coberpedi with the aircon blasting no problems. Temperature didnt go above half. Now sydney to wolongong makes me uncomfortable.
Theres no mods its a stock str 3 diesle.
By the way ive been reading about bypassing the polution gear. But visually the turbo seems to not have a built in waste gate. My truck breathes a little heavy too so i think a catch can should be put in.

what colour is the coolant and has it been maintained?

 

[Hobs]

I have a similar problem i can drive around for weeks on city freeways at 110kph but as soon as i head down the Hume highway toward Bowral from Cambelltown the temperature goes up, it could be because its a gradual climb all the way it gets to about 80% on the guage ive changed the thermostat and the cap coolant was changed about 2 years ago,
On the way back it sits in the middle of the guage, could be the radiator needs a flush?

Simlar problem! Its the same. It starts the twmperature raise about 10 kms before the pheasnts nest service stations. Then its heater time all the way to cooma

 

[Hobs]

Coolant is fine. I think ill replace the radiator and water pump and a new thermo stat. Id like to doem one at a time but i gotta do the timing belt. Im suspecting the radiator may be blocked internally, thats why the heater works. The water pump ill be able to see wear and tear. Either way ill have practicle spares for my kit.

 

[tanz]

Hobs,

Get the flow checked in your radiator. I'd suggest it is partially blocked and restricting coolant flow. While you're at it change the thermostat, but I shouldn't think that the waterpump is at fault (unless of course your coolant has been REALLY neglected).

Cheers.

 

[Old.Tony]

Ok. Couldnt get it to overheat ( double demerits and all ) but at normal running temp the fan spins rellatively easily. Maybe about 100 grams of force at the tip of the blades.

That's too light. I'd suggest the clutch in the fan is no longer any good. Take it to a mechanic and have them verify that before spending money where it's not needed.

If the fan isn't being driven hard, it's not hauling air in at the higher RPM where it's really needed and won't be lowering the coolant temps.

Yes it could be the thermostat as well, but given that it functions normally until you start to load it up, I'm going for the clutch in the fan.

 

[Old.Tony]

I have a similar problem i can drive around for weeks on city freeways at 110kph but as soon as i head down the Hume highway toward Bowral from Cambelltown the temperature goes up, it could be because its a gradual climb all the way it gets to about 80% on the guage ive changed the thermostat and the cap coolant was changed about 2 years ago,
On the way back it sits in the middle of the guage, could be the radiator needs a flush?

I'd try spinning the fan with the engine HOT but turned off (so, drive it around to normal operating temps, pull over and try it). It should be fairly hard to turn over.

 

[Hobs]

Ok ill pull the fan off tommoro and see how it works. Im asuming it has a filling and drain cap of some description. Oil wise i pretty much use delo 400. Also used that in my bike gearboxes and never had clutch problems. Would it work in the fan?

 

[Old.Tony]

The manual doesn't indicate that the coupling is serviceable at all - it basically implies "if it doesn't work, replace it", but that's pretty standard for the manual.

Page 48/56 of CO.pdf:

INSPECTION AFTER REMOVAL
Fan Coupling
Check fan coupling for rough operation, wobbling, oil leakage or bent
bimetal.

It says absolutely nothing further.

 

[tanz]

I don't believe the fan is the issue as it's designed primarily to pull the air when road speed is slow. Some cooling fans actually inhibit airflow above 80kph (whilst operating normal).

However, if you do wish to test it. get engine up to normal operating temperature, then place a piece of cardboard between the radiator and condenser. When the fan hub starts to lock up you will hear a loud roaring sound and the fan will be blowing heaps of air!

Belt slip could also cause the same fault, but usually you would hear that. I did have a vehicle (not a Navara) through the workshop prior to christmas that the harmonic balancer had let go and at highway speed the alternator light would flicker and then it'd overheat, back off ad it was fine.

Cheers.

 

[scooba_285]

could be a leaking head gasket, has a subaru that did this n it was the head gasket