OK so as I've said in other posts, I just bought this jeep 3 days ago. It's a 98 4.0 sport 4d with 89xxx miles. The previous owner installed 2 electric fans and had them wired to run whenever the jeep was on. I bought a thermostat switch that operates by turning the fans on via a relay and a probe thermostat inserted through the radiator fins. It kicks on both fans at about 220 till it cools down around 208. Well tonight we decided to check how the 4x4 performs and we did some mildly moderate offroading. When I stopped on an incline to scout the crest of the hill, my gauge JUMPED from 220 to 250 and the warning light came on. I let it sit on the incline for about 8 minutes with the motor off but the power on to run the fans and it cooled down to about 210. I got over the hill to a flat spot and turned it off an we hung out for about 15 minutes. We then went about 4x4ing. I came to a much smaller incline and stopped to look at the city lights and the alarm went off again and the needle jumped. This time it took less time to cool off (I assume because the incline was less) about 2 minutes. we decided to head home (12 minutes off road and 20 minutes highway) the temp stayed around 209 and there were no issues.

I feel like the water pump isn't pushing the water while its on incline, or the temp sensor is giving me false high temp readings (because of how fast the temp drops and jumps) but I don't know. What are your ideas what do I need to do to test them and repair what you think is the issue?

Just had all fluids changed and filled yesterday so the radiator is full.

 

I like to "verify" any potential overheating temps with an infrared point and shoot thermometer pointed directly at the thermostat housing. Want to be sure that what you are seeing on your gauge is real.

Whenever you have signs of an overheat, it is time to evaluate every single component in your cooling system. They all work in lock step. Radiator, water pump, fan clutch, radiator cap, thermostat, hoses. How old are these components? If you are unsure, I'll tell you what I would recommend if this were my vehicle and I planned on keeping it. I would replace the cooling system wholesale. That's right. Every one of the above components. Unless you have paperwork to verify that something has been replaced recently. The price for all of these components combined is not really that much if you can do the labor yourself. And once you tear it apart and drain the system to replace something like the water pump is a good time to replace the other components. Finish off with a verified 50-50 concentration of conventional (green) coolant. I buy my thermostats (195 degrees) directly from Jeep for best reliability and coolant temperature control.

Overkill? Not hardly. One lesson I learned a long, long time ago. No better money spent than that spent on cooling system maintenance.

 

Well when they installed the two electric fans, which are working properly, they had to remove the mechanical fan and clutch, so I can eliminate those for now. I don' have acces to a thermo gun right now. According to the PO (which means nothing) the radiator has been replaced. One thing to keep in mind is this ONLY happened when stopped on an INCLINE. There hasn't been any issue on flat bottom. It might happen when driving uphill, but I haven't driven on an incline long enough to notice.

BTW I'm not writing off your suggestions

 

If all cooling system components are functioning correctly and the efans are running, sounds like the efans are too small.

 

have u checked ur coolant levels.

 

Something to consider, if you check everything else & come up with nothing.

The water jacket of some engine blocks contain machining chips from the factory. This looks like rusty steel wool, that gets trapped at the bottom of the water jacket.

If you remove all the freeze plugs, and find this stuff it can be removed.

You use a garden hose, and a wire coat hanger to get it all out.

I have had this happen in an old Duster with a 318. After cleaning, that engine ran cool as a cucumber.

It's a bit of an effort to do all this, and you should use brass replacement plugs if you do it.

Save it for last on your list of things to try.

 

Nag my fans are adequate. They cover 95% of the radiator and are all one piece. I replaced the temp sensor on top, but everything has to line up just right for the problem to happen so it may be some time before I know if that was the issue.

 

Somethings not adequate, right? It's all about the fan Cubic Feet per Minute pull rating of the fans. Do u know what your efans are vs stock CFM?

 

No I don't, but whenever the fans kick in on flat surface at idle, the temp drops from 220 t0 208 in seconds. At this point it looks like I have to see if the error duplicates. thanks for the input. I'll let you guys know what happens.

 

It's normal for coolant temp to increase some, after coming to a stop, but not 250F and the warning light on. Stopped is when the least amount of air circulates thru the rad. That's why I'm just guessing the efans are a shade small. Increased load on motor (going up an incline) will increase coolant temp. Air is pushed thru the rad, when the vehicle is moving, along with the air that the fans are pulling (if running). Stopping the vehicle drastically reduces air flow thru the rad, leaving air movement all up to the efans. Unless I found a very recent receipt in the glove box for a new rad, water pump and t-stat, I wouldn't presume BS from the PO as to what's new/what isn't.

Is the new fan controller adjustable? Can the on temp be set lower?

 

well I changed the temp sensor. I ran the truck for 5 sec. with it disconnected just to throw a code and have Autozone check it for other codes and clear it out. No other codes.

re connected it, cleared the code, ran it in the driveway for about an hour, then went and did a little 10 minute 4x4 session using pt4 and 4lo parked it on a 40º+ incline for 5 minutes ("low washer fluid" came on ha ha) and the fans and temp all worked as I felt they should. So I wasn't able to duplicate the error. I'll keep a close eye on it the next few days.

 

My 2000 was also set up with 2 electric fan when I bought it. After I cracked the head I put the manual fan set up on it. this kept the temp to about 195 to 210. Then one of the local gear heads told me I needed a shroud. long story short went back with complete factory set up now the jeep doesn't break 205 even towing with it. p.s. I agree with everyone else get the parts for the cooling system from jeep I went thru 3 raads and 2 therms from autozone.

 

I want to actually put the stock fan on and run an electric to the side of the rdiator or over the top (if there's enough clearance) if not I'll add a scoop

 

I dont know if the set up on a 98 is the same as the 2000. the 2000 came with a belt driven fan that takes up a lil more than 1/2 of the rad. and an electrical fan to the rest of it.

 

The thermostat probe I bought has an option of connecting to the AC so that when I run it, the fan runs too as well as when the temp reaches a certain level. I need help finding the correct wire to splice into. The closest I've come is the part that runs the cold air (top front of the motor) but that only runs it a few seconds at a time just as that part runs. I want to hook it to the AC fan that runs consistently when I turn it on. Everything else I've tried turns the fans on to run constantly with the ignition again. I do not want that.