So I cracked my head, put a new one on, started up my Jeep and within 5 minutes it start's over heating far above 210, almost to red. Put a new thermostat in, new heat sensor, haven't yet flushed the radiator, or put new coolant in. There's no smoke coming out of the engine or tail pipe. Where should I start?

 

4.0l, straight six.

 

Fans and fan clutch. How are they acting?

 

Why do these things always overheat?

The Grand Cherokees don't have this problem.

 

First and foremost, you should verify with a temp gun that the your gauge is giving you an accurate reading

 

What year? Always include that in your post. Significant differences along the way.

The XJ doesn't always overheat; the XJ has no systemic or design issue. I've never experienced one on ANY of my Jeeps. It is subject to the same forces at play for every vehicle. Worn out components create overheats.

Verification with an infrared point and shoot pointed directly at the thermostat housing is never a bad idea.

You should have thoroughly flushed the radiator when you had it torn apart. What thermostat did you install? I buy plenty of aftermarket parts, but I buy my stats directly from Jeep. 195 degrees only. Is the head a salvage yard head or where did you source it.

The more detail you give us, the better we can help you.

 

It's listed in his title

 

Owner neglect is usually the number one cause of just about any 11+ year old vehicle malfunctioning/having a problem. The Grand Cherokee 4.0L rad is larger, they have substantially more surface area than the dinky Cherokee rads. With a larger radiator, an owner can neglect it longer before it plugs up and overheats. If XJs always overheated, there would be something like 3,000,000 overheating threads (number of XJs built). Sometimes I feel like I've responded to all 3,000,000.

Installed a new head, t-stat and sensor but didn't do a flush or re-fill with fresh coolant?.......really?????

 

<--- one of the patients