Little help. Running cool.

Shiftee

Member
Joined
May 30, 2014
Need some help. Can't figure out why my 4.0 runs so cool. I've never heard of a wrangler running cooler than 200 without a problem. I can drive 3 hours to the beach at 80 mph/3k on the tach and still be sitting just over the second tick mark. (I assume around 180) It's been running cool since I got it but I had bigger fish to fry with re-gearing and getting the txf case to stop leaking. Then my idler pulley decided to come off the other day and after replacing it I noticed the fan clutch was out. So I replaced that and like most things with the jeep turning one bolt turns into a full service weekend extravaganza...

I've...
drained and flushed
reverse flushed
flushed with water and compressed air
flushed the heater core with water and compressed air
run zerex's cleaner for two days (drove 250 miles)
drained the block
flushed some more

thermostat is less than 6 mo. old (stant 195)
water pump is less than 6 mo old
I have decent heat, actually is quite warm

Right now I've got the stat housing/water outlet off and I just tested both the old stat and a new 195 deg stant. Both seem to operate right around 195.

My coolant was pretty sick when I drained it. A little disturbing for the fact that it was changed about 6 mo ago with the stat and pump. I reverse flushed until it was clear. Then after the zerex clean it was pretty sick again. Flushed till clear.

I don't have any white smoke coming out the tail and running to operating temp (albeit low) with the rad cap off I have no unusual bubbling/burping.

I have noticed that my evap solenoid is rapidly clicking during warm up. Shouldn't it be off during cold starts? Could I be staying in open loop?

I just picked up new coolant temp and air temp sensors as well as a new stat housing/water outlet.

Wouldn't bother me too much but I seem to be running really rich.
I'm at the point where I just don't wanna throw any more money at it without running it by you guys. I'm gonna install the new sensors and housing and give it a shot, unless one of you wise men have any ideas I should check first.
 
Shiftee said:
My coolant was pretty sick when I drained it. A little disturbing for the fact that it was changed about 6 mo ago with the stat and pump. I reverse flushed until it was clear. Then after the zerex clean it was pretty sick again. Flushed till clear.
Click to expand...
Was it brown nasty sludge? My guess would be exhaust gas getting into the coolant, by the headgasket. Doesn't necessarily have to blow white smoke.. You neglected to mention what year your vehicle is. Since you have evap controls, I would have to say its '96 or newer.. Have any codes/CEL/SES light on?
 
Sorry about that. 98 TJ 4.0.
I wouldn't say sludge. There isn't really any thickness to it. There was some small particle/debris sediment. Looks to be rust but I haven't had experience with exhaust contaminated coolant before so I couldn't say it's not. PO stated that the headgasket had been replaced recently but I didn't know the guy from adam... he could have told me the headgasket was 14k gold and I'd have just as much faith in it's accuracy. That was about a year and a half ago. But isn't overheating a central characteristic of a blown headgasket?
 
I'll defer to the experts like @Jody Treadway but...
Before you start troubleshooting make sure you have an issue.
The factory gauges really ahve 3 positions cold(t-stat aint opened) - somewhere close to normal- OH FAWK Shes about to melt
Ideally you'd plumb a mechanical sender in and set a quality gauge in eye sight.
Absent that pop the cap and let her idle a while and stick a good high temp thermometer in the fill neck and see what temp you are running.
 
Replaced the stat and housing along with the coolant temp sensor. Running like a champ now. Heated up and idled right at the "2" in 210. Only thing that still concerns me is how filthy my coolant was after such a short change interval. So next step should be a compression test to check on that head gasket?
 
I don't know what year your Jeep is. but in the late 90's there was a run of 4.0 blocks that tended to rust excessively from the inside out. I want to say somewhere around 98 or 99 models. At the dealer we had to replace the short block, radiator and heater core while they were under warranty. If there were out of warranty, the got the garden hose hooked up the heater core treatment for a few hours.

Point being, don't worry about the rust so much as that can be fixed. It sounds like you had a bad ECT which was giving the PCM an improper signal which was in turn relaying an incorrect message to the cluster.
 
Nothing to do with the running cool, but more so with the dirty coolant. A buddy of mine has been wrestling with a nasty coolant issue in his 4.0. ends up it was a leaky freeze plug letting air in the system. as Jody said, they had issues with excessive rust issues inside the block. you have to keep all air out of the system and if there's a leak of any kind, well, then you get air in it.
 
Thanks for the input guys. I'll keep an eye on the coolant and see if I'm still having rust issues. I did find a leak in the bottom side of the thermostat housing. Things seem pretty tight at the moment. Putting everything back together I found that the spacer behind the idler pulley (non adjusting one by the alt) was missing. It wasn't turning freely and putting a bit of drag on the belt. Threw a 10.9 washer on it for the time being. Between that and a warm engine it feels like a whole new jeep. Well it did anyway, driving home last night my blower resistor burned out and the motor (on high) sounds like it's about to take off. Also getting a "whoosh" from the brake booster. Pump em a couple times at idle and the engine stumbles a tad. So now I've got a couple other demons to track down. Anybody else feel like every time you fix one thing it somehow leads to two more things breaking?
 
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