Nissan Repair: Overheating problem, radiator cap, head gasket

Question
QUESTION: Nissan 1400 2006 small pickup overheating when in traffic. Once moving and there is airflow over the radiator then it cools rapidly down. We have replaced the thermostat and water pump. The radiator seems to be fine.(tested by checking the core - water flows evenly through it) There is no water in the oil and the water level does not drop. We had to install an electric fan to cool down for she gets so hot that the petrol pump stops functioning. Any other ideas please.

ANSWER: Hi Michelle -

I have a couple questions -

Is the electric fan you installed in addition to the existing? Is it running all the time?

When was the last time the radiator/cooling system was flushed? Although you can see flow on top, there could be restriction on the lower half, where sediment and rust can collect.

Let me know -
aloha
calvin


---------- FOLLOW-UP ----------

QUESTION: yes it is installed in addition to the original fan, and we installed a switch in the cab so we can switch it on when the vehicle starts getting hot. The radiator was flushed 2 days ago and it is clean inside. Do you think that changing the radiator cap can help to improve the problem? or do you think it can be the head gasket that is not functioning properly or even a port in the block that is blocked. Do you think that there could be little water flow in the block itself? I don't want to overhaul the head if not necessary...any other ideas would be greatly appreciated...

ANSWER: Hi Michelle -

If you are not losing water, then the radiator cap should be fine.

Couple more questions:

Does it overheat to the point it is boiling over when in traffic, or does the needle just creep up?

What temp thermostat was installed?

Thanks
calvin

---------- FOLLOW-UP ----------

QUESTION: the needle just creeps up till almost the end - then the motor gets so hot that the fuel pump does not pump fuel.(it is a mechanical fuel pump) we cool it down with water and the it starts working again,  not sure of the temp of the thermostat.. it is the standard that all of these vehicles run on...do you think it could also be faulty electrics?

Answer
Hi Michelle

I do not think it is anything electrical.
Try this - remove the thermostat and try running it like that. At the same time check the stamp on the thermostat, it should tell you what temp (in degrees) it opens. Could range anywhere from 160 to 195.

Thanks
calvin