bherd

Hi all,

I just extensively rebuilt my '83ZXT including putting in steel braid lines wherever possible in place of stock rubber hoses.

I have a rough idle which I was going to let the local Nissan mechanic look at and also check emission's, set lash, etc.

One problem I would like to fix first if I can is it overheats. I changed the thermostat before I noticed that the BOTTOM radiator hose gets hot and the top stays cold. It's almost like the water pump is running in reverse. There is a slight difference in the way the water hoses appeared to be routed compared to the 82 manual, the heater hoses don't have any T connections or bypass path when the heater isn't running. (I didn't think to try the ooverheat with the heater on, I am kinda freaked out by how hot it gets so fast) fan belt appears tight on the water pump, and I am using an electrical fan which doesn't turn on because the radiator never gets hot.

It seems like it would be the thermostat except it almost feels like the thermostat isn't opening because the coolant isn't circulating and therefore isn't hot up by the thermostat.

Does this sound familiar or what is a good way to make sure the water pump is running correctly? I read you can squeeze the upper hose but since it clearly isn't getting that far I haven't tried specifically.

Also I didn't run the water through the throttlebody, is this needed normally? (Ran it to the turbo instead)

TIA,

BH

RodMoyes

Is the water pump new? what condition are the impellers in? I would hope that when you rebuilt the motor you put in a new water pump...


Otherwise,

Sounds like a bad radiator.


Rod.

chinesekid

i was thinking water pump.. if not the radiator.. but you can be like me and change both at the same time.. hahaha

EatmyDust

it woudn't be a bad idea to check your thermastat as well.you could have trash coght in ther.

bherd

Water pump is new, no squealing either. Is there ports that might be blocked by putting the gasket on badly?

Radiator was flushed pretty good, didn't have any visible debris or stuff in it.

Thermostat was changed, I am thinking about getting the old one out of the trash and testing it but the amount of heat in the lower hose was very strange.

BH

theramz

Although you no doubt had the block and head boiled and flushed there is almost always some debries left in and I have found some considerable amouts in mine. You could try back flushing the radiator with the lower hose off.

DGriffin

If I remember right putting the head gasket on badly or (upside down???) could potentially block coolant passages.

NismoPick

Oh snap! Thad be crap-apy!

Bherd... gotta start somewhere... pull of some hoses while the motor is running & see where you have pressure, and where you don't.

bherd

Yeah, I was wondering what a good pressure test was, I was thinking about disconnecting a hose and blowing coolant all over the place. So far I have only heard that you can feel the pulsations in the upper hose once the thermostat has opened.

BH

jmmorriso

what does the gauge say? is the dot on the thermostat facing up, or did you make a booboo? the lower would get hot before the upper anyway I think, since the lower carries coolant away from the motor right? mine had a stuck closed thermostat forever and never overheated, well the piston fell off so coolant flow still prolly pushed it open a little.

bherd

Conclusion:

The engine wasn't overheating, I had converted from digital to analog dash and should have changed the temperature sender type. I used an infrared thermometer to ensure I wasn't really cooking the engine and the thermostat did open up correctly and all of the little strange hot spots went away with coolant flow.

I just had to have the confidence to let the temp gauge peg in the process.

Thanks to all who wrote.

bherd