1996 12 Valve Operating Temperature Issue

[KnightHawk]

So, I have a 96 12 valve, auto with 210,xxx. I am having issues with my truck not being able to maintain a proper operating temperature. This is what is happening, I will turn the truck on it will warm up to 190F and will maintain that temperature while idling. The issue is, when I start driving the temperature will fall to 140F or below and this process continues to happen while I am driving. (i.e. warm up to 190F then thermostat opens and temperature drops to 140F)

The parts I have replaced...
-radiator
-clutch fan (currently off vehicle to see if it would help the truck maintain operating temperature)
-thermostat
-water pump
-radiator cap

Other issues along with this...
-truck doesn't produce any heat (i know this is not directly related, but prior to this issue occurring my truck would produce amazing heat.) I had an issue of over heating when I moved to Colorado for the summer and realized my clutch fan was bad, so I replaced it and fix the overheating issue)

I am living in Alaska so heat is kinda important.

 

[Timd32]

The thernostat swing seems normal, the newer trucks 98.5 maybe and newer the computer compensates for the swings and it just shows a more steady temp.

No heat I would check the heater hoses in and out since you have no heat, if they are both hot I might suspect a blend door issue where its stuck on cold.

If its stuck on defrost only I would check for a vaccum leak possible, or an actuator issue.

Other might chime in here with corrections or the sort as I agree heat is nice.

You might need a winter front for your truck and Im sure you are already very fluent with your block heater and the sort being 100% operational, the cords and the ends are easy to replace the element should be pretty decent, but make sure thats working as expected.

Good luck hope you find a quick answer.

 

[NIsaacs]

No cab heat and low engine temps, sounds like your system is low. After an overnight shutdown, is your overflow bottle at the full mark? If you don't bleed the air out as you fill (crack heater hose or loosen pipe plug in head) they will not fill well and takes several overnight shutdowns to correct. If the system is low the t-stat won't work right.

 

[BigPapa]

As stated, that temp swing is quite normal. Mine’s done it for over 500K now with no adverse issues. Mine is also slow to build heat on a really cold morning. I find if I let it warm up good for 3-4 minutes with my high idle device holding it at around 1200RPM and the fan on the 3rd position it has decent heat when I get in and warms up totally in @ 5 miles.