Nissan Repair: 2007 Nissan Altima, head gasket leak, nissan altima

Question
Driving down the highway with the cruise set at 70 mph and start up any incline the gauge starts going up and the airconditioner will shut off.  If you slow down to 60mph or less or driving in town,  it will go back to normal.  We have taken it and had all diagnostics done. All was good.  We replaced the thermostat and it did not help.  Can you tell me what could be the problem?

Answer
John,

If it has been checked and it only does it under a load try premium gas and see if it is a light spark knock causing it.  If so, a Nissan dealer can use the Consult III scantool to retard the timing via a computer setting.  If not have the vehicle inspected for a small head gasket leak or a crack in the head.