Temp gauge problem for 4.0
 

On a cold day, after about a 10-15 mile drive the temp gauge will barely get above the cold mark, the heat works fine. In the morning when i start it the temp gauge reads way below the cold mark and slowly creeps up just past the cold mark. Just trying to figure out what is wrong before i replace parts. This is on a 98 4.0 with a non tach gauge cluster.

Maybe the thermostat is stuck open? Cheap part to replace, i would start there

If i replace the rad. cap will that help?

mine has been doing that since i bought the truck. killer heat, but the gauge always reads low.

mine does the same

I just Had this on my 04 4.0. If you are running cool the thermostat is stuck open. You should get a cel... code po128 I think??? On the other if the gauge is reading low it is probably the sending unit. There is 2 senders on the thermostat housing. One for the gauge and one for the computer.

Oh and rad cap will not help.

Hmm funny thing is, i am not getting a cel

You may not get a CEL with the thermostat being stuck. You will just see an obvious difference in operating temperature after the engine is warmed up. I just replaced one in my mom's S10 that was stuck closed (engine was overheating while driving, cooled down when stopped). As a temporary fix, we pulled the thermostat and let it run wide open. The engine stayed so cold that it never would come close to reaching operating temperature which in turn made the heat take forever to get hot. Thermostats are cheap and easy fixes.. replace it and I can almost bet you will have fixed your problem.

Sometimes its the Needles inside the instrument Cluster it slips. I changed my needles from the stock white to the red ones from a crown Victoria. I just had to move each one by hand to dial it in. My temp gauge is actin up right now, and I don't feel like opening up the cluster again. I was just thinking about putting a gauge pod with the temp engine gauge in my truck to fix the problem but never did it before.

My question Is what size fitting do I get for the temp engine gauge( the fitting is already mounted to the gauge right?. what size will fit my engine. My truck is a 2002 ranger xlt 4.0 auto. and where does it connect to? have a pic where it connects to?-thanks

Ran my 5.0 without a thermostat for a few months.

Honestly wished I hadn't put one in, now it likes getting hot.