Strange overheating problem.

[Rickedl]

Car specs; 91 240sx le hatch.
Everything is stock or oem replacement
Recently replaced battery and alt.
126k miles

Obviously the car hasn't driven that much in its life. I picked it up last winter (Jan and live in Central Il) and as I was driving it home It started to get hot. But it didn't overheat. I let it idle for a few minutes and it went right back down to Operating temp. Have had no problems until recently. August I notice it is getting hot on me again, here is the cycle it goes.

Start up.
Start driving it goes to Operating temp.
After about a minute it goes to just under H.
A few minutes later it returns to Operating temp.
If the car does not cool down to cold it will work fine, if it does start over at top.

I have just replaced the thermostat with a KNOWN GOOD stat.

I have no leaks,
Fans work just fine and the fan clutch is just fine.
The only thing I haven't chanced is the water pump and the radiator.

I would go after the water pump but after it gets hot it works just fine.

Thank you for your help.

[compactfean]

Have you checked the temp when its hot (gauge) with a temp gun? It might not be over heating.. I would check the temp sensor for the gauge. Also did you bleed the air when replacing t-stat?

[Chaotic_Warlord]

When you changed the thermostat did you properly bleed the system? That's your problem, the KA is VERY temperamental if when the cooling system is touched and not bled properly afterward.I chased cooling system gremlins for months after I did anything with my cooling system because I could never get the system bled properly. Every time I thought it was bled properly it would be fine for a couple of weeks and then it would run hot and then once the thermostat would open it would run cold even and stay cold unless I shut the car off, then it would be fine.