poolguy1995

I know this is the season for overheating questions, but I've been chasing this problem for a month, and can't seem to beat it.

I bought the XJ about 3 months ago, around town I have had no problem, drove to Tucson a month ago, and began to overheat 150 miles down the road. I only have the idiot lights, so I don't know how hot, I just cranked up the heater whilke waiting for an exit, and the light kicked off after 2 minutes. I stopped, let it rest, and finished the trip with no problems - never lost coolant.

I got home, I pulled thermo, flushed radiator -looked really good, bright green fluid, no rust or crap, new thermo (195*), new temp sensor/sending unit, filled and burped. Still great around town, but 2 weeks ago driving to Vegas did the same thing as Tucson trip -idiot light after 200+ miles, heater cooled it right off, rsted, and finished trip no problems. While I was in Vegas though it started giving me the warning light after just a few minutes in stop and go traffic with the AC on. I flushed everything again, bought an aftermarket temp gauge, and a fan clutch. The gauge I'm having trouble swapping out because 99 doesn't have the temp sending unit on the back of the head like everyone else, but it is in the thermo housing, and cannot be pulled, and sawapped, because it sends the info to the comp to run the closed/open loop and will throw codes, and run crazy lean. I piced together a brass "T" to run both sensors out of the thermo housing, but neither read correctly that way as they were both out of the "flow" of coolant. I bought an infrared thermo, and I get good readings across the radiator telling me I don't think I have an obstruction there, I have burpes the system several times, I have replaced the replacement thermostat, and I have ordered a scan guage that will be here tomorrow. I also replaced the water pump just in case, and the lower radiator hose I replaced with the spring supported one that can't collapse under load. I don't want to just replace the rad just because its next on the list, can anyone tell me if I'm missing something else to check out before I jump on to radiator barn and order a new radiator? I have still never lost any coolant, no leaks, and no boil overs. The head looks good, no coolant leaks, and no oil in colant/coolant in oil.

Thanks for your help! I'm at my wits end with this one...

OverlandZJ

When your idiot lights goes on did you notice if the auxillery fan was also kicking on? The square black plastic one.

It should kick on around 220*. If it's not that could be your issue, it would essentially give you that little bit extra like your getting with activating the heater.

poolguy1995

I've only had the light come on when the AC was on, I know the aux fan is on with the AC, but I'm not sure if its coming on based on the heat alone.

milmat1

If this is happening while traveling (Highway) The fan shouldn't be a problem, The fan would likely be a problem at slow speeds, idling around town etc..
You turn on the heater and it helps so I am thinking Circulation problems.. i.e. Clogged radiator tubes maybe ?? Feel the radiator's fin surface, Is it hotter at the top than at the bottom (or Vice Versa)..??
Maybe even the Bottom (Suction Side) hose collapsing under highway speeds...??

Just Some Thoughts for you...?

poolguy1995

I replaced the lower hose with the factory spring hose( it has the spring inside the hose to keep it from collapsing), the other hoses seem to be okay. I replaced the water pump thinking circulation was probably the culcprit as well, but it didn't help much... I thought if I had some blockage that a good flush would at least wash out some crud, even if it couldn't clear the blockage, but even that was a really clean flush...errrrgh!!!

djb383

Not much help here other than I suspect the radiator and/or idiot light. The XJ rad is really small so everything about the cooling system has to be in top notch condition to avoid overheating, especially this time of year.

Please post back with your ScanGauge results.....we have one in our XJ and don't think you will be disappointed, especially since it can be moved from one OBD-II vehicle to another.

milmat1

What are you calling a scan gauge?

I am really thinking the radiator, If you could take both hoses off and flush it backwards (from top hose inlet) It might help.

djb383

http://www.scangauge.com/

Sometimes scale build-up inside a radiator can become so hard that flushing won't phase it. A rad flush is kinda like a laser/touchless car wash....if your car is really dirty, no touchless car wash in the world will get it clean. The rad must be removed, and taken to a rad shop. They will remove the tanks thus exposing the tubes. Then they insert cleaning rods the full length of each tube. This process, known as "rodding out", scrapes/removes the scale build-up from inside the tubes. Once this has been done and the external condition of the rad is still good, you essentially have a new rad at a fraction of the cost.

fantic238

if the outside temperature is above 100 farenheit it is quite normal. Put the AC on normal and step off the gas a bit.

kbad

hey poolguy....you say that you flushed the rad a few times, but have you flushed the whole system?.... and have you checked the voltage at the temp sensor connector from the computer? these have a combination coolant temperature sensor that also feeds the gauge ...also, you can test your temp sensor without removing it from the pump housing....check the resistance of the temp sensor, hot or cold, hot should read very low resistance across sensor connector and cold should read very hi resistance...you can remove the sensor and place it in hot water to check resistance as well....your aux (electric) fan kicks in with the a/c and/or when temp is above ~215, turn on the a/c anytime and it should come on.

everything you have done to it sounds like it is good to go. although you have changed them, double check your thermostat (maybe go with a 180 for your area, seems like you need your cooling to kick in a bit sooner! ...Thermostat discussion going on here... https://www.cherokeeforum.com/f2/thermostat-51586/ ) and sensor functionality....everything depends on them!

although this applies to the renix engine, troubleshooting tips are still very valid.... http://www.lunghd.com/Tech_Articles/..._Diagnosis.htm ...and here.... http://www.lunghd.com/Tech_Articles/...iagnostics.htm

good luck!

poolguy1995

Thanks for all of your suggestions/links...good stuff. I think I need to go ahead and bite on the radiator. I think I will jut swap in the 3 row from radiator barn - is this the consensus on the most effecient option?

milmat1

I just installed a new aluminum rad from radiator barn myself. Everything Fit Perfectly and went smoothly. I cant say enough good things about radiator barn !

poolguy1995

New Question,
I can't get the new radiator for a few days because it has to be ordered, so I though I would do a couple of new tests, could somebody help me digest the results?

Coolant system pressure test:

I borrowed the test kit from Auto Zone this morning, and did 2 tests.
First was the cold engine, crank the pressure up to 16 psi, and watch for leakdown. the pressure dropped down to around 11 psi over a 10 minute period, but then held at 11 psi for 30 minutes without moving. I then released te pressure, and then started te jeep, and let the pressure build on its own - it SLOWLY climbed to 7 psi, but then stayed there. I tried revving the engine, holding a steady higher RPM around 2000, and the pressure didn't really change.

My interpretation is that I have a leak somewhere ( thus the trickle down psi on the original test), however, if I wasn't climbing psi rapidly with engine running, it is probably not a head gasket. I just can't sem to find the leak anywhere, and I have never lost coolant.

To confrim the gasket, I did an engine compression test, and all of the plugs looked good, no coolant in any of the holes, and the compression read as follows :
1-166 2-169 3-169 4-170 5-169 6-172
I couldn't ask for a better compression result right?

Are there anyother test i can do with the coolant test kit b efore I return it, or any ideas an how I mighjt be misinterpreting my results?

Thanks

milmat1

I would wonder if maybe the initial cold test, You pumped up to 16 psi, Maybe there was some air trapped in the engine somewhere allowing it to drop down to the 11 psi. Because if it remained at 11 psi for 30 minutes I don't think you have a leak....?
What If After it dropped to 11 psi then you increase it back to 16, Will it stay at 16 psi then ??
I cant think of anthing that would bleed off until 11psi then stop...Strange !!

poolguy1995

You could be right Milmat1, when I pulled the pressure gauge off, I burped the system, and I got a ridiculous amount of air out of it. I think I may have been p[ressurizing some of the air pockets - if that makes sense. I will let it cool down, top it off, and burp it again and see what happens then. Thanks for your help...