ok, rebuilt my 99 4.0 in January, PO kept driving after blowing the lower rad hose and toasted #1 &#2 pistons. replaced all hoses, water pump and thermostat at that time. moved to SoCal, overheated while sitting at Border Checkpoint a few weeks ago. replaced rad with a new 2row aluminum one, and a new fan clutch for good measure. it runs around 195 locally, but still overheated last Friday on the I-10 in AZ running the a/c at about 80mph in maybe 97 degree weather. electric fan comes on as it should. due to the utter lack of quality of the Chinese made CHAMPION RADIATOR with it's incorrectly machined unsealable flare fittings and useless oversized quick disconnect fittings, I added a Hayden (made in USA) tranny cooler in front. what's left??? new coolant at rebuild and again this week, might be around 70% glycol by now. I did not replace coolant temp sensor, but it seems to be ok. Help!?!

 

It won't solve your problem, but I'd go with some hood vents just get rid of some under hood heat.

 

that might be an ok idea for the summer, but I kinda want to find the real problem. these things didn't overheat when they were new, so there's gotta be something gone wrong...

 

I would over heat all the time in traffic, then I got a new aluminum rad, fan clutch, water pump, 180 degree thermostat, and rad cap, runs at about 182 now, I can sit in traffic and it will reach 200 max.

People will say you need a 195 thermo because that's what the computer is set for to achieve optimum fuel mileage, to those people I say I'd rather spend a little more at the pump than have my engine overheat.

 

I think I'll get a 180 or 185 degree stat. I heard Stant has a line that're guaranteed plus or minus 3 degrees. maybe throw a sender at it @ the same time. it ate the water pump bearings and the TPS when it blew up for the PO.

 

If like to hear how that goes. All my cooling system has been replaced and its not uncommon or my 91 xj to hit 220 when in the city or off road. I read a lot about how people strongly suggest staying with 195 t-stat but I'm ready to give a 180 a try

 

How hot/what temp is "overheated"? We've momentarily seen 230 (ScanGauge) and that's not overheating, according to the factory. Driving fast, in really hot weather, running a/c could be considered "extreme driving conditions".

I know nothing about the radiator u installed but it could be smaller (thinner core), have less fins/", less heat rejection capability than the OE factory rad. Just because it has 2 rows doesn't mean the core is twice as thick. The OE factory rad is really dinky so going with something different than a OE 1 (very wide) row stock style rad could be an issue.

Is the rad fan shroud intact/in place? Big tires? Anything blocking airflow to the grille? So many questions.

......and for what it's worth, a 180 stat will allow it to run a little cooler MOST of the time.....but not when driving 80, in 97 ambient, running a/c. We run a 180 stat and like I said, we've momentarily seen 230, 3 digit ambient, stopped on black asphalt, running a/c. Factory idiot light never flickers so momentarily hitting 230 is not overheating.

 

fan shroud is intact and in place, electric fan in place and operating. new 195deg thermostat was installed in January when it got it's new pistons (and about $750 worth of other stuff) is it possible the thermostat isn't opening all the way? I might also hang a good aftermarket gauge on, or invest in a scan gauge to leave connected so I can keep an eye on other stuff as well...

 

fan shroud is intact and in place, electric fan in place and operating. new 195deg thermostat was installed in January when it got it's new pistons (and about $750 worth of other stuff) is it possible the thermostat isn't opening all the way? I might also hang a good aftermarket gauge on, or invest in a scan gauge to leave connected so I can keep an eye on other stuff as well... oh, and the radiator is designed to replace the original, and has 2 columns of flat tubes running crosswise between what looks just like the fins on the original. the vendor claims it's good for 400hp.

 

.....but how hot is "overheating"? In the "red"? Big tires? As a temporary test u could always remove the t-stat to see if u get the same overheat temps under the same driving conditions. U can test the stat in a pan of water on top of the stove using a cooking thermometer and visually observing stat open/close. Don't boil the water.

Overheating when everything in the cooling system is new is a stumper. I'm just leary of some aftermarket stuff and I'm not knocking the new rad but basically it's the only thing different. If the core is the same thickness as OE stock (1.25" wide/thick 1 row), then the 2 rows added together are less than OE stock due to the space between the 2 rows. The space between the 2 rows does nothing. Again, overheating with a new motor and new cooling system is a stumper. Go back and review to see if anything else changed from before to after.

 

As the other guys are saying we need a little more information of the vehicle in question. Big tires? Stock Gears? Obviously its a Automatic as you said you installed another Aux Cooler. Because of the area you live in I'd look at bypassing radiator as your trans cooler. If your cruising down the highway at 80mph with big tires there's a chance you're heating up the cooling system from the hot tranny fluid.

 

All stock, no lift (minor butt sag from tired springs), fresh 235/75 15's, not 30-something's. I used to rent these when they were new and don't recall making any hot, though I never set out across the Sonoran desert doing 80 in 100 degree heat, either. I'm either going to try a new sender or buy a ScanGauge. I define "overheat" as the check gauges light and buzzer, with the temp gauge pretty well out of places to go...

 

The head might have cracked internally when it overheated.

You would likely not see it off the vehicle (the crack) as the head is cold. Magnafluxing the head probably would not show the crack.

Stay with the 195* thermostat. OEM MOPAR is the best if you can find it.

Use 50/50 coolant mix. 70% cuts down on the heat transfer.

 

Clutch fan condition ?