Coolant temp sensor
 

Hey guys,

I could use some of your expert knowledge here.

My 97 3500 7.4 is running hotter then I like. It used to hit 200 as a norm but recently its been climbing 230 as of today.
This is what I have replaced and tested. Sorry that its so long but I had to try before I bug ya'll.

Radiator-Replaced
T-stat-Replaced 180/15lbs cap
Temp sensor on L/S (Drivers)-Replaced
Water pump-Replaced
Bypass hoses (Heater)-Replaced
Cooling system-Flushed twice (Including heater core)
Rad cap-Replaced
Fan clutch-Replaced
Aux fan relay-Replaced
Pulled the Aux fan and tested directly to the battery. It works.
Now for the other items that I tried.
Turned on the A/C and tested the plug to the aux fan it worked for a min then no power at the connector going to the aux fan plug.
Tested the relay It works.
The radiator needs coolant (50/50) every two days. No puddles anywhere?
I thought the head gasket was gone but I did a block test yesterday and no its not gone.
I tested the rad system yesterday as well and it held 15 PSI.
I now heard a rumor that there is another coolant sensor next to the t-stat housing but its getting to dark right now and will have to check it tomorrow.
Does anybody know if that's correct????
What am I missing???? This thing should be frozen even here in Cali....

Re: Coolant temp sensor
 

I would start with verifying you gage is right. You have replaced everything else.

With an infrared thermometer you can check the temp at the sensors, radiator, thermostat housing and know if it really is overheating.

Re: Coolant temp sensor
 

Good call.

I had my OBDII hooked up and it was showing 199 not the 230 like on the gage.
I still need to test the Coolant switch itself. I'm pulling the plugs and putting a borescope in the cylinders tomorrow.
Strang thing tho. My Aux fan turned on when I fired up the A/C then shut down? Oh well I do wish I was a mechanic. I don't like the unknown.

Much appreciated amigo.

Re: Coolant temp sensor
 

My Suburban always shows around 170 is and MAYBE get to to 180 with a 190 thermostat. Everyone says it should be around 190-200. Assumed the sender was bad and after a lot of horsing around and replacing the sender I got an infrared thermometer. Turns out it was right, with the 190 t-stat it would just barely get to 185 or so at the thermostat housing. Lesson learned, never assume, verify.