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Discussion Starter · #1 ·
1997 TJ 4.0 auto trans 31" tires. I have searched and read hundreds of threads,but no one ever posts if they resolve the issue. Jeep runs 172-181 (according to obd2 scanner)degrees consistently I have tried 3 different 195 thermostats, installed correctly, all open as they should in pot on the stove around 192-196 degrees according to non contact thermometer. You can watch the temp rise and fall as thermostat opens and closes. New carquest radiator. All Interior heat is actually pretty good. Rebuilt longblock, less than 3000 miles. New AC Delco water pump. New mopar coil, cap, rotor, wires, champion copper plugs, new cam sensor. New mopar coolant temp sensor, IAT. Have swapped complete known working throttle body with IAC, MAP, TPS, new gasket, no change. New NTK upstream o2 Has slight miss at idle, no codes, no rythmn, random. Sprayed 3 cans of carb cleaner all over engine, no rise in rpm. My train of thought is that the lower temp is causing computer to overcompensate rich, which is causing the misfire. Why is it running cool? :pullinghair:
 

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I went through this same problem and recently resolved it - kinda. My symptoms were low temp like you but I was also blowing my top radiator hose off frequently due to really high pressure in my cooling system.

What I believe was the problem was my thermostat. I bought it new from Advance Auto. It wasnt the same as OEM. Upon buying another from a Jeep dealer I saw that the Advance Auto one didn't have the breather valve. A few things lead to me to believe my low temp was the result of an air pocket.

First is my hoses were swelling and blowing off on a regular basis. I theorize that the lack of a breather hole was not allowing air to escape into the overflow.

As far as where the air was coming from - I have those worm drive hose clamps. When I recently pressure tested I found that nearly every one of them was leaking. I am guessing that upon cool down when the vacuum pulls the coolant back in I was pulling in air from a leaky top rad hose. By the way, I burped my system on several occasions trying to solve my swollen hose issues.

Upon replacing my therm with one that has the air valve my temperature and pressure issues are gone. I still have the worm clamps on all the hoses and still leak from the top inlet slightly. I will tackle those when it warms up. My radiator is a Griffin and I'm not convinced the inlet port measures to OEM spec. Not sure if I'll ever fix the leaking.

Hope this helps. I won't say with absolute certainty that my problems are solved yet but I'm getting closer.
 

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Discussion Starter · #3 ·
Interesting, I have used a Stant and two Super Stants. Maybe next stop is dealer. When I put everything back together my OEM spring clamps leaked and had to switch to screw clamps. Oh and new fan clutch as well.
 

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Interesting, I have used a Stant and two Super Stants. Maybe next stop is dealer. When I put everything back together my OEM spring clamps leaked and had to switch to screw clamps. Oh and new fan clutch as well.
Yeah, I'm at a loss on these hose clamps. I've had this Jeep for a year and a half and it has never not leaked coolant. I've replaced everything. It's literally a green dot on the bottom of my rad now but it's still a leak. I'm convinced it's my Griffin rad. The upper hose just go us on too easily. There's barely a flange on it.

I put about 3 of those Stants in before going OEM. I suppose you could drill a hole in your Stant and position it on top. I've read of others doing that. When you replace be sure to properly burp. You'll find plenty of write ups on here.
 

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Is it simply a misfire problem that is the bottom-line issue? Do you get multiple 43 codes in the odometer display when you turn the ignition key on-off-on three times within five seconds to start the diagnostics routine?

If so, you may simply have the dreaded bad batch of weak valve springs problem the '97 and '98 4.0L engines were infamous for... as my '97 4.0L engine had. The fix for that is, if you're lucky, new valve springs.... but if you're not lucky and the problem has gone on so long it has damaged the valve seats, a valve job.

The temperature has nothing to do with that particular problem, if it's from weak valve springs.
 

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Discussion Starter · #7 ·
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These plugs have about 1500 miles on them. I have since swapped to champions with no change in operating temperature or misfire. No codes. Averaging about 12 mpg.
 

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As others have stated, use the OEM thermostat. When I put in my stroker, I used a high flow thermostat from Hesco along with their pump and thermostat housing and it ran cold. According to my scan gauge it was running at 182F. I replaced it with an OEM thermostat and problem was solved.
 

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Discussion Starter · #11 ·
Two dealerships and $150.00 later much of my issue is resolved. The $25.00 mopar thermostat increased the operating temp up to 195 give or take, but while talking with the parts guy, he suggested that my crank sensor may be to blame. I thought they either worked or failed, but he claimed that sometimes the wires get damaged but still send signal. But the resistance is incorrect. This was on of the last few original parts, so I sprung for the $125.00 and upon installation, the miss decreased tremendously. A test drive felt like I had one or two extra cylinders, much better throttle response and power. I believe my timing is now advancing properly and may not have before. Not calling it cured yet, but well on its way.
 
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