LS 430 Overheating.

[Mile_High_Flyer]

My 2005 LS 430 has recently been getting very warm when working a bit harder than standard. No, not thrashing it, just working a little harder, like going up a hill. The dash temperature gauge sits on its normal position, just above the centre mark. However, I have an HUD display plugged into the diagnostic port, and it shows the rising temperature.

I have just put in a brand new radiator because it was leaking from a crack in the top tank, no difference. My original first thought was a crack in the head or block, but no sign of water in the oil, nor oil in the coolant, and I can't smell anything apart from antifreeze in the coolant, but that may not necessarily be correct, my sniffer may not be as good as it might be, at my age!. It looked clean when I drained it. My next thought was water pump, but it was changed 30,000 km ago, so it should be fine. Or a  thermostat not opening fully, but that I haven't checked.

.The fans are turning on at about 93 degrees.

The strange thing is the different reading on the dash temperature gauge, although it appears to work fine up to that normal point.. Checking the actual water temperature suggests the HUD is reading correctly.

Does anybody have any ideas?  Thank you.

[mikaelse]

Change thermostat is a good guess will fix it.  Those can start to only open halv way. They often do fail over time