Unknown overheating isssue 2007 navara d40

[Greg323]

So my navara overheated and i saved it just before serious engine damage. I pulled over and steam came out of the overflow tank. Temp gauge was almost at the limit. I let it cool, topped up with coolant and away i went no worries.
No idea what has caused it to overheat to begin with.
I took it to my usual mechanic to check it out and all they could find was a dodgy thermostat.
I got it back to try out but it is still over heating and the mechanic is having issues trying to find the cause.
They have flushed the radiator, pressure tested engine with 100psi over 12 hours for head damage, emissions test, replaced thermostat, inspected and tested as much as they could without pulling apart the head, looked for leaks but the coolant level doesnt drop, no milky or grey oil on the dip stick, still runs well just over heats.

-Driving at low speeds around town its fine but as soon as i get to the highway and climb long gradual hills the temp rises quickly.
-AC has no effect on the overheating ive tried it with and without the ac and fan.
-from a cold start the engine reaches normal operating temp after driving 2-3kms but cools immediately when i pull over.
-temp gauge jumps up and down instead of climbing slowly.
-egr cooler tank seems fine with no blocks.
-idle is great and drives well with no hicups (apart from overheating)

Does anyone have any other ideas and suggestions?

Thanks

 

[jonney]

maybe the cooling fan centric hub needs replacing. this will cause overheating but at slow speeds it still is ok.

 

[Old.Tony]

I'm wondering about that viscous hub too. If it's failed, the key factor in making the engine heat up is engine load - we notice ours when we're towing and we reach a hill. The temp does climb quickly!

However I can't help but think there's something more that's not right here. The temperature gauge is driven by the ECU (unlike the fuel gauge which is a pure voltage-feedback from the fuel tank sensor) but I've never seen it just bounce around. The trick is, where is that particular fault?

If it's an instrument cluster earth (often upset by working on the stereo which shares the earth point) then earthing the stereo will settle the needle down. If it's an ECU earth (also common) the earth point under the ECU needs to be cleaned, reconnected and sealed with a spritz of electrical sealer.

I would be interested in knowing what the ECU thinks is happening with the temperature. If the temperature itself is bouncing around, then the coolant temp sensor or its wiring harness might be dirty/corroded. I'm having little issues like this with my car now and mine's two years younger (although I've submerged mine to the windscreen in the past). My right-hand indicator in the headlight assembly is erratic as is my left hand light assembly and sometimes the left indicator activates the reversing lights causing poor blinking at the rear and my in-dash camera monitor activating. I'll be cleaning them with contact cleaner, reassembling and then using electrical sealer to keep it clean.

I would suggest a similar activity with your coolant temperature sensor - give it a good clean, if everything's working then make sure it's watertight.

 

[jonney]

but would any failed electronics cause the engine to overheat ?

 

[Old.Tony]

It's vaguely possible but quite unlikely especially given how the symptoms are occurring. I agree with your diagnosis - most likely the viscous hub. The rest addresses the odd needle behaviour.

 

[jonney]

yes Tony just curious about the electronics on the D-40,s as you never know what they control these days.

 

[Old.Tony]

If it were electronics that were responsible for actual overheat (and not just an indication of overheating) like the OP has experienced, it would HAVE to be something to do with fuel/air mixture and/or injection timing. Imagine if cylinder 1 injected at the correct time, as did cyls 2 and 4, but cyl 3 injected during the piston's rise to TDC (ie before the natual injection point post TDC) causing cyl 3 to combust and try pushing the piston back down, slowing the engine, then the ECU compensates by increasing the fuelling providing more power ... I can see an engine overheating rather quickly if this happened.

It's as unlikely as all get-out though. If the ground became faulty for the injector it would simply stop injecting (or become erratic but still at the correct time). In order to open the injector, an electrical pulse has to arrive on the injector's harness. The only thing that's going to do that is either the ECU, a physical short or perhaps an EMP - and if your car suffers an EMP large enough to introduce sufficient inducted voltage on the injector cable for long enough to cause the engine to overheat, you'll be either more worried about other faults/failures or you'll be cooked yourself.

So electronic causes for actual physical overheating wouldn't be a common thing. Indications can become faulty easily due to sensor/electrical faults. Finding the fault is sometimes not easy, hence the common failure points listed.

 

[Greg323]

The radiator was 3/4 blocked. After pulling off the top radiator tank and flushing it from the bottom water was only coming out of about 12 fins, 4 on the left and 8 on the right. The rest was blocked. Put a new radiator in and its back to normal. Thanks for the posts with some ideas and help.