okay i was driving for about 2hours on the highway - hot day, A/C on, temp crept up to just past 3/4 of the way up the gauge. Air started to blow hot. Shut off a/c gauge went to half. Turned A/c back on blowing cold again but gauge temp started to climb again. Shut off A/C turned on heat and gauge went down to normal??? Whats happening?

On cool days I have no problems. Warm / hot days temp only climbs when i idle and goes down again when I'm driving. i was told this is normal, but i don't think so.

Coolant level is okay, Checked fan control timer/modual is okay, Fans run but not sure if they kick in at the right temp, When the engine is hot both the upper and lower rad hoses are firm and hot so Tstat should be okay,

Checked the Engine Coolant sensor and when the engine is cold the Resistance is lower than is should be according to my Haynes Manual (around 1500 book say 2200-2700) the voltage from the conector is okay 5V. Could it be the sensor???

Any thoughts would be greatly appriciated, I've been having this problem for a while now and would really like to get it resoved before the hot summer months get here.

Thanks

 

any coolant leaks?

is your cooling system full?

Is your tstat stuck partially closed?

Clogged radiator?

those are the things I would check first.......

 

How do i check for a clogged rad?