Making a TJ Cooler

The write-up below was sent to me in e-mail from Scott Kruize, a local Phoenix Jeeper who runs a nicely modified ’97 TJ.  Scott recently started having over heating problems and tried a variety of things in an attempt to keep his temp gauge in the normal area.  There had been an ongoing exchange of comments and suggestions over the past week or two on the AZVJC e-mail reflector.  Here are his summary comments, posted here with his permission, on what he did to resolve his problem.  He wrote:


My TJ is now running nice and cool. It feels good to be among the living. I can’t wait to go wheeling this weekend.

In all of my observations below I used a temperature probe to get my readings at the thermostat housing where the temperature sending unit screws in and at the radiator where the upper hose comes in. I felt this was more accurate than relying on the factory gauge for the sake of comparison. I got a few strange looks from people when they saw the multi-meter zip tied to the fender when I was test driving it but how else was I going to get an accurate reading? I did find that my factory gauge was very accurate. I did not notice any variation between my measurement at the sending unit with the probe and what the gauge read. I’d like to note that I have also installed new hoses, a new 195 degree thermostat, and back flushed the system before making the following observations. I ran the AC on Max for all of the tests just too. I was getting temps around 268 degrees before I began making changes. Now lets get on with my findings.

The Flex-a-lite Wrangler II electric fan is crap. When the outside temperature is over 100 degrees there is a big difference between the stock mechanical fan and the Flex-a-lite electric at idle and while driving. When idling it’s around 25 degrees and when driving its around 20 degrees. It’s already packaged up and ready to go back for a refund. Need I say more?

The new 3 row radiator from is installed and has definitely dropped my temperatures down to normal. Just installing the new radiator resulted in a 30+ degree drop in temperature. Definitely money well spent. I’m sure some of the damaged fins and possible blockage of the stock radiator reduced its performance below normal so this isn’t necessarily the kind of performance increase that those of you with a clean stock radiator may see. There has been some talk on the Jeepsunlimited forum about there possibly being tap water in the system from the factory. There is no way to prove this theory just a few others who have had mineral deposit problems in their stock system despite never adding any tap water into it. I recommend that everybody flush their system every year and refill with fresh coolant and distilled water just to be safe.

I’d also like to recommend that those of you concerned with temperatures try a bottle of Redline Water Wetter. With a 50/50 mix of glycol/water its supposed to drop the temperatures by 8-10 degrees by increasing the heat transfer capabilities of water. My experience is that it works as advertised and highly recommend it. For $6 you can’t go wrong. I bought mine at Loper’s Performance though I’ve also seen it at Desert Rat Offroad.

Don’t underestimate the restriction placed on the system by bugs or seed pods stuck in the AC condenser coil. If airflow is reduced here then its also restricted at the radiator. I carefully unbolted the condenser coil from the grill (I left the lines connected) and spent 4 hours reaching into the engine compartment with a tweezers and blow gun getting it cleared out. (If you don’t have an air compressor in your garage, why not? This is probably THE best thing I’ve done for my Jeep hobby in the last 7 years) I bet it was restricted by 10%. My temperature findings were only affected by a few degrees after I cleaned it but this is still enough to have a big impact on your AC performance. I noticed that the AC was blowing quite a bit cooler after I finished cleaning it out.  

I’d like to add something more to this before closing. The fuel injected 4.0 liter (as well as the 2.5L) is designed to run at 210 degrees for maximum efficiency and emissions. It is critical to run a 195 degree thermostat or you will run in a continuous cold start mode which will create a rich mixture from the computer and reduced engine life. Don’t run a lower temp stat unless your running a custom map adjuster or a computer chip that is designed to run at the cooler temp. I have always run a 195 degree stat. Its okay to go with a high flow just don’t drop a cooler stat in. No matter what mods you do don’t expect to see the gauge dip much below 210 since this is where its designed to run. If yours is running cooler than this when warmed up then you need to find out if your thermostat is stuck open. If your running hotter than you need to look into this too.

I will not be installing the Flowkooler water pump. I’m going to send it back with the electric fan. If my engine is running at its designed temperature of 210 and the radiator temp probe is 188 degrees I guess I’m running efficient enough that the thermostat is opening and closing even when the outside temp is over 100 degrees. I see no need to take this any farther. I do recommend that those that have Jeeps carrying lots of extra weight from mods and/or gear or those towing trailers to give the 3 row radiator and the Redline Water Wetter a try.