wierd heating problems

[weezys 240sx]

My 1992 nissian 240sx is heating wierd. The temp gage shows hot,but the engine doesn't seem to be hot. On cool days it doesn't show hot. Days above 70 it shows hot. checked everything and changed things. The old radiator was leaking I got another from junk yard,since then wierd problems. I have no signs of a bad head.I don't know what it is. The radiator I got is supposed to be the right size.

[Fixer67]

Are you using a 50/50 mix in the radiator? In the newer cars you can not use straight water. Older cars had a water jacket temp of 180-190 degrees New cars sometimes have water jacket temp of 220 or more. Just a though. Also check your sending unit and the wire going to it. If the wire shorts to the frame it will show the engine red hot when it is froze in a block of ice,

[silvia240sx]

check the thermastat

[weezys 240sx]

Hi fixer67, Yes I am using a 50/50 mix. This all started when I changed radiators. I have changed thermostat,flushed radiator, had the head checked everythign I can think of to do. The gage still shows hot,I really don't know if the engine is really hot or not. I have not changed the sensor.I bleed the radiator to get the air out.I have a 5/8 in. radiator in now. Not sure if the old one was a 1in. or not.The outside temp. seems to make a difference. Can't run air cond. All help needed please!

[Fixer67]

OK. Try this, get a something to read temps in the range of the car (180+). A cooking thermometer works good. Remover the radiator cap and start the engine. Read the temp on the Gage and the thermometer. That should help give some idea of where the problem is. That way you should know if the engine is really overheating or not. Does the sensor that runs the gage mount into the block or the radiator? If it mounts into the radiator and the radiator is not the same size as the one you took out it may not be reading right even though it is good. Also water flow rate can mess with you. If the water flows too slow the motor will overheat because the radiator may not get rid of the heat fast enough and cause it to overheat. If the water flows too fast it will not take heat from the engine because it is not in there long enough. Oh, I should have asked sooner, did you put the fan shroud back on? If the shroud is not on and on right air flow over the radiator will not be enough to cool the radiator and the engine will overheat. Good Luck.

[ricebike]

that temp gauge sensor is near that air bleed bolt? maybe a trapped air pocket there or you have a crappy junkyard radiator.

maybe air is getting into a loose clamp? borrow a pressure tester from a local parts store (ie autozone). pressurize to ~14psi, then check for leaks.

When I changed my radiator to a full metal lifetime warranty one, i had air trapped from the top of the block to the top radiator hose. Bleed it 2x and everything went back to normal for me.