XJ Underheating

My 92 4.O aw4 xj is not warming up fully, it's running a tad past 40' CELCIUS on a cold day. My heat is warm, but not hot. I've replaced the tstat, and guage sensor. Hooked it up to a diag machine, all my sensors were fine, and the temp guage is acurate. Testing my old tstat(195'f), it opens up at 225'F(thermometer might be a little off). I have no idea what to do next. Any ideas? The mechanic said to replace the tstat again, because they sometimes have "bad lots."

Thanks

Try replacing the thermal fan clutch, it might not be freewheeling properly, and may be fanning the radiator when it shouldn't.

i put a fan clutch on my 92 laredo recently since she warmed slowly, and then ran a bit too hot. (florida's winter is easy)Now she heats up in minutes, and runs cooler too.

I have an 88 XJ 4.0 and I am having the same problem. I popped the hood after reading this post and relized that the fan is running full time.