New Zealand Datsun Club

Was the thermostat in the right way around? Did you take the time to bleed all the air from the system? Is your fanbelt nice and tight? If you roll electric fans, (sorry I can't remember) are they working correctly?

Failing that, perhaps have your radiator rodded out as Dan suggested? They remove the top and bottom tanks, and poke a skinny steel rod through the tubes and remove any deposits. It unreal how much crap can accumulate in the tubes.

I put the new thermostat in the same way as the old one so I'm guessing that it is the right way round. I flushed all the water out and then refilled and it seems to be running ok without overheating so far. Perhaps I hadn't bled all the air out of the system like you said Bart. Is there any special technique to do that or do you just leaving running for a while and continue to top up with water/coolant?

I'm rocking a viscous fan

all engines are different. Some motors you just run em with the radiator cap off till all the air comes out. Most newer engines actually have a bleed screw in the head/manifold. I've even heard of motor where you remove the temp sender to let the air escape.
How far did you drive it before it heated up? If you did a couple of hundy kms, then I doubt that was the cause, but if you only drove halfway accross town, (Not that I'd know how far halfway accross your town is) then chances are it was air that caused it.

Bartman wrote: but if you only drove halfway accross town, (Not that I'd know how far halfway accross your town is)

About to the end of your street bart lol

Haha nice one Dan

I'm actually in Hamilton at the moment, I can drive for about 15 min and then it sometimes seems to get hot. I say sometimes because it seems a bit random. I drove to work (35 - 40 min away) yesterday and it started getting hot (got to about 3/4 on the gauge) but on the way home it didn't seem to do it (got to about 2/3 and just sat there). Then when I drove it again later it got "hot" again...
Reallly annoying. I'm going to go down to the Nissan dealership and see what a genuine replacement for my original thermostat looks like. I'm starting to run out of ideas...

What temp sensor have you got, one that suits the engine or one that suits the gauge? Are they compatible? Is the gauge accurate? Does it smell really hot or is the gauge telling you it is hot? Does it boil or blow water out? I guess you have been keeping an eye on hte water, is it staying about the same? DO you have a catch and return system on the radiator to keep it full when cold?
The thermostat works by heating wax in the base of it to push open a valve as it expands, the wax needs to be on the hot, engine side of the valve, so normally the short pointier end pokes out and is covered by the Thermostat housing. Generalisation. I may be preaching to the choir, but hope this has helped in some way.
You may need to put a thermometer in your cooling system and see if the engine is 'getting hot' or if the gauge is telling porkies.

I used the temp sensor out of my L18 so it is matched to the gauge. I don't think the engine smells very hot, but then it has always run cold with the other thermostat in (I took the thermostat in to a radiator place and they told me that it was buggered). I'm running a catch and return system on it and the water doesn't seem to be going down. It sounds like I've got the thermostat around the right way. I'm going to take the car into a place and get them to test the cooling system and see if they have any ideas.