Et guys/gals I have an 89 renix and te temp of the engine doesn't go much over the 40 mark on the gauge is that bad?

 

Yep. You need a 195* thermostat for your Jeep to perform well. Can you verify if it's actually running that cold or if the gauge is reading inaccurately?

 

40*c=104*f
Thats WAY too cold.

 

I had the same problem my thermostat was stuck open

 

haha no help here but my xj likes to reach out to 240 every start up and then come down and run normal

 

And I've heard now that you must flush the rad out before putting in the new thermostat I know it's the best thing to do but I live in Canada and its -19 outside so I really don't feel like flushing the engine hence I have no garage if it was the summer I'd do it but ya lol and I've change thermostat b4 and never changed the antifreeze never had a problem befor

 

I always flush my coolant system while changing the thermostat ill usually change mine every 6 months for comfort and to know its new my coolant system run like a top right now ( Knock on wood )

 

And yes I know it's running cold and not just the gauge cause my heat is freezing cold lol it blows just barely warm air

 

Dont worry too much about flushing the system, just drain it, put in your new thermostat, and refill with antifreeze/water.
Very important:
When you put water in a radiator USE DISTILLED ONLY
Tap water has minerals in it, and this is what gunks up radiators.

Does it run at regular temp during the summer?
If so, change the thermostat first and see if that fixes it. If not, I would just block the radiator with a piece of cardboard behind the grille.