purplegorillaxj

I was driving home the other night and my jeep just shut off while driving, check engine light comes on. All my other gauges were reading correct temp is showing 190 oil pressure at 50PSI when it shut down, volt gauge at 14. I let it sit for a minute and it fired right back up and I drove it home. Hooked up the code reader and it gave me a P0118 Eng Coolant Temp Sensor High Voltage which I assume either I have a tear in the wire going to the sensor or the sensor is bad. What is confusing me is the fact that my upper radiator hose is hot but the radiator cap is cold and the cooling system has no pressure at operating temp and the lower radiator is luke warm. I have no leaks, plenty of coolant and my belt is new. Im thinking thermostat? any opinions? 99 Cherokee sport 4.0 automatic 4wd

red4dr

did you happen to feel the small line coming off the water pump that is going to the heater core? I think that would point in the direction of water pump if it was cold too, but if it was hot then I think you are right with thermostat.

Roler

The thermostat what? Not opening or closing? Your upper radiator hose is hot, your engine temp is 190, your thermostat by definition is opening as it should. Is it stuck open? Your running temp is ok (maybe somewhat low-ish, but nothing concerning, and if your engine warms up reasonably quick, it's unlikely to be stuck open. So I would not suspect a faulty thermostat.
The fact that your lower hose is significantly cooler, suggests there is adequate flow through the radiator which is doing what is should do. Massive WP failure is not consistent with that. Your temp sensor code is more likely to be due to an electrical/sensor issue...

freegdr

Hot water flow thru top hose cooler water out bottom hose. Have your system pressure checked dont forget to do cap also.

djb383

I would not think any of what was described in the OP would cause the engine to shut down.....not sure why that happened. Wonder if there's any impeller left on the water pump?

It's really quick and easy to test the t-stat in a pan of water, on top the stove using a cooking thermometer. Do not toss the stat into boiling water.

Roler

His hoses are hot (top) and cooler (lower)....I'd think that there should be considerable flow through the radiator to make that happen...

purplegorillaxj

The faulty sensor I kno will cause vehicle stalling, but as I mentioned it seems funny that the radiator cap is not hot after driving for 30 mins and has no pressure behind it right after shut off

djb383

I doubt that P0118 would shut the engine down.

Heat rises/stays at the top, air or water. If coolant is not flowing properly (by the rad cap), lower areas of both the motor and rad (and rad cap) will remain cooler longer. Here's a non-leaking, non-flowing water pump.

red4dr

this is what I was thinking. That the wp was not moving water, and the hoses were just that temp because they are closest to the engine for the heat to dissipate to.

djb383

I'd think if there was considerable flow (thru the radiator), temp difference between top and bottom would be very little.

Roler

Interesting....so what do you expect a good functioning radiator to do then, djb?
I'd say it should cause enough cooling of the coolant, for the radiator hoses to be obviously different in temp....

djb383

I expect a good functioning, properly sized/designed radiator to never let coolant temp exceed 10*F above the t-stat rating, regardless of driving conditions....I know, I live in a dream world.

Will a good functioning radiator have the same inlet/outlet coolant temp drop in freezing ambient vs 3 digit ambient? Inlet/outlet coolant temp differences depends heavily on driving conditions AND coolant flow.

In freezing ambient temps yes, there will be a significant difference in radiator inlet/outlet temps due mainly to very slow coolant flow. In 3 digit ambient temp, stat wide open, no, there will be very little difference in rad inlet/outlet temp due to very rapid coolant flow. When the thermostat is wide open, coolant flow is at max (water pump speed). The reason the stat is wide open is, the cooling system has been maxed out by the driving conditions.

Size matters, when it comes to rads and the Jeep XJ engineers must have been out on the golf course the day space for the raditor was being designed/determined. The XJ rad is ridiculously small at 1.27" sq. inches core surface area per CID of the motor (4.0L). Most other vehicles have rads that r 2+ sq. inches surface area per motor CID.

purplegorillaxj

ok I have replace the thermostat and coolant sensor, but after driving if for roughly and hour today the gauge hovered at 210 which is normal for my jeep. however I popped the hood immediately after shuting it down and my radiator cap was luke warm and I could stick my finger in the coolant, there was no pressure behind the cap. im going to throw a new cap on it today just to rule that out

freegdr

Did ya pressure check system yet ?

purplegorillaxj

No sir but that next on my list today