hot-under-collarTom Chudleigh (Whyalla, SA)

Hi Allan, I have an intermittent overheating problem with my 1988 D21 Nissan Navara with the 2.4L petrol four. Under normal driving the temp needle stays right in the middle, however if I take it on sand or even drive up a long hill it will start to badly overheat. Weirdly, if I put in neutral and rev it, it will come back down after a couple of minutes. If I leave it on and keep driving as normal it will stay hot until I shut it off to allow it to cool down again.

Also, when I open the cap before I turn the engine on in the morning, the coolant is filled right to the top of the radiator with the overflow approximately a third full, but if I check it when it’s hot, the overflow bottle is full as can be and I can only assume the radiator is low on coolant.

Any ideas what’s going on?

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hot-under-collarTom Chudleigh (Whyalla, SA)

Hi Allan, I have an intermittent overheating problem with my 1988 D21 Nissan Navara with the 2.4L petrol four. Under normal driving the temp needle stays right in the middle, however if I take it on sand or even drive up a long hill it will start to badly overheat. Weirdly, if I put in neutral and rev it, it will come back down after a couple of minutes. If I leave it on and keep driving as normal it will stay hot until I shut it off to allow it to cool down again.

Also, when I open the cap before I turn the engine on in the morning, the coolant is filled right to the top of the radiator with the overflow approximately a third full, but if I check it when it’s hot, the overflow bottle is full as can be and I can only assume the radiator is low on coolant.

Any ideas what’s going on?

 

Allan

Hi Tom, the water leaving the radiator when it’s hot and returning once it’s cool again is exactly how it should be working. There’s no problem there; water simply expands when it heats up and fills the overflow bottle and there’s a valve on the radiator cap to let it back in again. As for your problem, the first thing I’d be checking is the fanbelt isn’t slipping at certain revs.

Check the fanbelt tension and make sure the belt is not actually touching the bottom of any of the pulleys. Check for witness marks on the inside of the belt. The other thing to check is that the thermostatic fan is working ok. The best way to do this is to wait until the vehicle overheats, leave it running, get out and lift the bonnet (watch you don’t get run over!) and turn the engine off.

Watch to see if the thermo fan stops with the motor or if it keeps running. If the fan keeps going, then the thermostatic fan is not operating and will probably need replacement.

It may also be wroth checking that the lower radiator hose isn’t sucking flat. A couple of those hose clamps around the outside of the hose can prevent this if you suspect its happening. One last thing is to make sure you’re getting adequate air flow to your radiator. Bullbars and driving lights can prevent sufficient airflow from getting in and can eventually cook your motor.

Ok pal, catch you later.