This community did an awesome job helping me through the fuse popping issue with my turn signals. So, I'm coming back to you folks again for help.

Long story short, something is off with my cooling system. First, there are no leaks, no obvious issues with the water pump or bearing noise, the fans seem to be working correctly, etc. I get great heat and there are no indications of overheating (though I suspect the gauge is slightly inaccurate) or headgasket failure. My 1996 runs and drives great, but I am getting what seems to be low fuel economy as a side effect.

So, I brought my IR heat gun along with me on my drive to work. It's about 10-12 miles and a mix of highway and mostly in-town driving and it was a pretty cold ambient temp in the single digits. No problems. I popped the hood and with the Jeep idling, I took a few readings of the thermostat housing. It read 195° and the temperature gauge was a needle width or two below the 210° mark. I figured things must be fine and the t-stat is opening, although I never did feel the lower hose. Not sure if I was in a hurry or it just didn't occur to me.

Anyway, took it for a run tonight, maybe 5-10 miles with an ambient temp of about 12°, mostly going 15-25 miles an hour around town (we got hit with a blizzard so things are pretty icy). Great heat, ran well, no complaints except fuel economy. The trip odometer shows about 50 miles on a new tank and the fuel gauge is a hair above 3/4 full, but that could be nothing. So when I got it back home to my garage, I popped the hood and used my IR heat gun again. I got readings of about 192°, 193° or so. Even still, I'd imagine the thermostat must have opened at least once, even if it closed up again. The top hose and hoses to the heater core were definitely very warm/hot but the lower radiator hose was cool, as though nothing had flowed through it. Using the IR gun on the engine block was an inaccurate waste of time, showing about 173°.

So, as best as I can tell, I'm not overheating, the Jeep is running fine and although it warms up at a normal rate, it's not necessarily reaching operating temperature and the lower radiator hose is cool/cold to the touch. I've owned and worked on many vehicles before, but I know they tend to have their own quirks, and I'm sure XJs do too. Has anyone experienced these symptoms and found an explanation or solution that worked for them? If there's more information needed, I'd be glad to share what I can.

 

in my 2000 in cold i get 200 in about 4 miles. never check lower hose but if water is moving thru i would expect it to be cool/cold, thats what the rad does,hot in , cold out, into the engine,gets hot again. oh, i quit checking mileage ,its low unless i would cruize steady far a 100 mile which i aint doing till i get more confidence in this new to me vehicle, little troubles i dont need in cold weather. to me,you sound good. im no jeep xpert.

am i missing something?

 

Thanks for the reply. I don't necessarily think you're wrong, I'm just confused why it appears my XJ seems to overcool or can't quite reach or maintain operating temperature. I'd suspect a faulty gauge if I hadn't used my IR heat gun. The lower hose should certainly be much cooler than the top hose, but it almost appears that the thermostat never opened.

 

what are your mpg's?

 

I can't say for sure. I've only been driving it occasionally for a couple weeks. That's why I have 51 miles on the trip odometer. Fuel tank senders aren't super accurate, but it seems it's pretty poor if it's just a shade above 3/4 with so few miles on. I'll hand calculate it when I fill next. My previous 2WD XJ got 18.5-19 MPG in the summer for reference.

Ive had a reliable source confirm it should be no issue for a '96 MPG-wise but the previous owner removed the downstream cat and O2 sensor. The upstream cat and O2 are functional and in place.

 

I just did some work on my cooling system as well, and replaced my radiator that had rusted out on the bottom causing some seepage of coolant. The gauges on these are not very accurate, but my IR heat gun at normal temp showed about a 25° difference between the upper and lower hoses. The thermostat will begin opening before 195°, and should be fully open at 195°. If your lower hose was cool while your top hose was 193° at the thermostat tells me something is not right with your flow through the radiator. I hope someone more knowledgeable chimes in on this.

If your downstream O2 sensors are removed that may affect the fueling and be giving you the poor mileage. I get about 16 in mixed driving, and that is pretty close to the overhead display. A cheap scan option is the TorquePro app with a bluetooth OBDII dongle to monitor the engine sensors in real time.

I would also change the radiator cap if it is over 5 years old.

Good luck on your troubleshooting.

 

It sounds like your cooling system is fine. With the outside temp being in the teens the lower rad hose would be a lot cooler than the upper hose. The bottom of the radiator is always cooler than the top. If you are reading with an IR gun in the 190's you should be good. If it were to fall into the 180's and less then the thermostat may be stuck opened. The reason why you are getting such crappy MPG's is probably because the use of a winter blend of gas. It has more ethanol in it then in the summer.

 

Thanks for the reply, Dan. I thought I might be acting paranoid or excessively wary. I suppose I might need a new temperature sending unit. Do you recommend using a winter blind or cardboard to partially block the radiator?

 

I think you're overthinking all of this and looking for problems where they don't exist. You say you have good cabin heat and are not overheating, so you don't have a clog. If you did have a clog in the radiator or at the thermostat, you wouldn't be running that cool and would probably be overheating instead. How hot the hoses are to the touch is really irrelevant if you're not having any issues.

The only actual symptom you have reported is a vague notion that you have low gas mileage that doesn't appear to be based on even a full tank of gas. CONFIRM your low mileage before you go looking for solutions for a problem that may not exist.

Yes, calculate it using math, not by trying to judge how much the gauge thinks you have used. The gauges are not reliable for judging the rate of fuel consumption because they don't always move at a constant rate across the dial. Mine likes to creep down to half a tank, then make a faster dive for empty because I didn't really have half a tank when it said I did.

Also, calculate it a few times over a few tanks of gas before deciding you have a problem. The automatic shutoff at the gas station isn't necessarily going to be the same at every gas pump, so you can't always be sure you have an accurate read of how much fuel you used.

A 4WD XJ has more drag on the drive train and will get lower mileage, even when you're driving it in 2WD mode.

Somebody correct me if I'm mistaken, but I think you should only have one catalytic converter on a '96. If your O2 sensor is gone, are you getting a CEL? If so, I would actually go ahead and fix that. The problem with relatively benign CELs is that you get used to seeing that light, and when there's a real problem that needs to be addressed, you don't realize it because your CEL is always lit.

 

Definitely need the cat and O2. The downstream O2 has a direct affect on fuel ratio.

 

can't agree with this more! And yes, you would definitely have a CEL if the downstream o2 is gone and/or the cat was removed. The downstream o2 tells the computer how efficiently the cat is working which will effect fuel trims. You can't just remove these components without some kind of issue. Computer would need programming or SOMETIMES an o2 fooler works but not always.

 

Yes, yes, yes, yes, yes!

Any estimation of fuel economy based in any way on the gauge is pure garbage.