It started to over heat while driving, I took the thermostat out and run it for half hour and it was great, then just now driving to work I notice its starting to run hot again, (no thermostat) get to work an it's just pissing out smoke and steam from the exhaust, It won't start at all now , the water was flowing great last night, so I don't think there will be a blockage? , can someone give me an explanation that's not worst case scenario . I'm honoring I haven't damaged the head or gasket , I wasent driving it hard either

I would do two things.

1. Visual inspection of radiator

2. Test the radiator flow. It costs nothing and is easy to do.

See http://datsun1200.com/modules/mediawi ... adiator#Trouble_Diagnoses

Blown headgasket.

Take out plugs, and blip the starter. Water will squirt out at least one of the plug holes.

Im just worried I may have burnt the valves , ill try it after work, I know I can fix it myself, the problem is getting the ute home, my mate is good with cares and he has said he will be able to start it to drive home, I don't Evan want to entertain what he had said?

Overheating does not cause burnt valves -- not in the A-series engines -- so no worries.

Burnt valves usually are caused by overtight valves, or by carboned valves -- the engine starts running rough and rather than fix it the owner continues to drive it, burning the valves.

On the other hand, when my radiator cracked on the freeway (100 kph) last September it overheated and within about 90 seconds warped the cylinder head. It wouldn't start and when I removed the plugs, water came out.

i'll make the call,blown head gasket, 100% sure.no mucking around.

lol brendon,cheers

I know these are silly things to mention, but I noticed how quickly they can cause your temp. to shoot up, and even if they don't help you, they might count for advice...

1 - Check if your overflow hose is properly connected.
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2 - Electric fan's wire polarity.
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3 - Fan belt loose. This is an easy one to miss!
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4 - Antifreeze/water ratio weak (especially in conjuction with a disconnected overflow!)
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5 - I've also noted that a bigger radiator mounted to an unmodfied body also heats up a LOT quicker.

Something you could check into is a product to clean out the corrosion in your water system. Usually a small bottle added to your coolent. This helped me quite a bit by making 2 (almost unnoticible) leaks evident.

Link for some advice/direction if it is the head gasket:
http://datsun1200.com/modules/mediawi ... tle=Changing_Head_Gasket.

maddatter1, I think you're on to something with the thermostat, but replace it, don't remove it from the equation too quickly! Smaller motors rely on the thermostat, especially with higher anti-freeze mixes. Next time you replace your thermostat, drill a small hole in the outer housing. For some odd reason this improves the thermostat life and prevents 'sticking'.

Datsun started fitting thermostats with the small hole in them in 1969, and by 1979 were in every Datsun. A-series will not overheat if you take the thermostat out. Also, running plain water with no coolant/antifreeze mix will not cause overheating either.

Quote:

I stand corrected =)