Coolant temp rise - Mystery?

[Ancient]

Hello,

After car is warm, coolant gauge starts to rise randomly then quickly drop back to normal. After driving for a while, hitting the gas will cause it to go up, but letting off the gas will bring it back to normal.


This just started happening

Parts replaced before the problem:
Thermostat
Radiator
Waterpump
Fan clutch

No smoke from engine and no coolant leaks.
Expansion tank is at normal level.

All parts are new oem and less than 6 months old.
What’s my next move?

 

[uscmas412]

What's the CEL code?

 

[Fj80oregon]

When posting issues post your year make and model or add it to your signature line so we know what you’re working on. If it’s a obd2 hook up a scan tool and verify your coolant temps.

 

[Ancient]

What's the CEL code?

O2 sensor and egr

 

[Ancient]

When posting issues post your year make and model or add it to your signature line so we know what you’re working on. If it’s a obd2 hook up a scan tool and verify your coolant temps.

1994 fzj80

 

[BTLSHP]

IDK, we drove DCTo Colorado in a refreshed 94 last summer. Temps were normal until we hit elevation. Turned out that my rebuilt fan clutch was the problem. We dropped a new one in and it stays below 210 in daily driving in the front range area. Sea level temps rarely went over 200.

Make certain the new fan is Asian or Toyota and the check the foam around the radiator?

 

[Ancient]

IDK, we drove DCTo Colorado in a refreshed 94 last summer. Temps were normal until we hit elevation. Turned out that my rebuilt fan clutch was the problem. We dropped a new one in and it stays below 210 in daily driving in the front range area. Sea level temps rarely went over 200.

Make certain the new fan is Asian or Toyota and the check the foam around the radiator?

Fan clutch is Asian

 

[jsloden]

I would be willing to bet you still have air in the system.

 

[CJF]

That went up so quickly that it seems it could be a problem with the gauge and/or sensor itself.

 

[Malleus]

This is normal operation, if you've modified the temp gauge...which leads me to believe that the gauge, or more likely, the flexiboard is at fault.

It's unfortunate that it's not a 3rd gen, or you could validate the gauge with an OBDII scantool.

 

[uscmas412]

You have an OEM radiator with an OEM radiator cap? DIY or shop installed?

Have you warmed up vehicle, let it cool for ~30 minutes, then tried to open radiator cap?