djb383

This afternoon I replaced top and bottom rad hoses, heater hoses, t-stat, t-stat housing, coolant sensor and the serpentine belt. I removed the old bottom rad hose at the pump which quickly dumps coolant. Then I removed the old top rad hose and the old top heater hose, both at the t-stat housing. Using my flex nozzle attached to the garden hose, I squirted water into the old top rad hose thus flushing the rad out through the old bottom rad hose. I then stuck the nozzle into the old heater hose and flushed the heater core out through the water pump. Last but not least, I flushed the cylinder head and block out the water pump by placing the nozzle on the heater hose nipple on the t-stat housing. A little compressed shop air blew most of the remaining clear water out of the rad, heater core and block.

Replaced the stock 195F t-stat with a 180F Stant Super Stat. Heater is warming up the cabin quicker and that's a pleasant surprise. Wifey and I drove around for little over an hour, looking at residential Xmas lights, and the ScanGauge floated from 181F to 188F the whole time driving slow, stop-n-go. Ambient temp was low/mid 60s, as we hit 70 today.

stumper

Nice, that's an easy way to do it. I like the garden hose attachment, makes things quick and easy.

thanks for the pics.

SeriousOffroad

Now put the correct t-stat back in. The OBD2 sysem will say in open loop mode if the engine doesn't reach normal operating temperature...and you'll pissing gas out the tail pipe.

pbgunrunner

at what temp does the computer switch over?

SeriousOffroad

195 Deg. F.

djb383

Apparently there's some confusion about open/closed loop engine emissions/performance management. Going to "closed loop" has virtually nothing to do with coolant temp but rather O2 sensor temp. There are 3 main components to "the loop"......1. the engine, 2. the computer, 3. the O2 sensor(s). O2 sensors must reach several hundred degrees F before they begin to function. When the engine is started cold, the system is in "open loop" with only the engine and computer functioning. Heated O2 sensors (ones with multiple wires) "light off" within a few seconds (less than a minute) of the engine starting and once they are functioning the system is in "closed loop". The computer is looking for, and striving to maintain, a 14.7:1 air to fuel ratio, not 195F coolant temp.

My ScanGauge displays both open and closed loop. Here lately, with A.M. temps in the low/mid 20s, you can see the gauge display go from open to closed loop within 30-45 seconds of start up however, the coolant temp has risen only a few degrees during that time. Best I can tell, the digital real time MPG numbers displayed on the ScanGauge are the same as when the 195F t-stat was in. Works for me.........the 180F stays.

SeriousOffroad

You are misinformed.

djb383

Nothing like being misinformed, so I guess the ScanGauge is wrong. After all, it only displays info that it receives from the ECM. You can clearly see the display change from "open" to "closed" loop under a multitude of different operating conditions whether the engine is at 195F or not. For example, when you hammer down on the throttle, the ScanGauge will instantly display "open" loop because under heavy throttle applications the ECM overrides the O2 sensor(s), giving the engine a richer mixture to avoid engine damage. Once normal/steady speed is resumed, the system returns to "closed" loop and the ScanGauge indicates same. Like I said, the ScanGauge, or any other instrument/tool/gauge, that plugs in to the ALDL port, just displays info it receives from the ECM. So when it displays "closed" loop, I believe the loop is closed and all is good in the universe. May the force be with you.

SeriousOffroad

WOT is in fact an OPEN LOOP Mode
Closed loop mode is not in effect until the engine reaches normal operating temps, and that is 195 deg F. That is the parameter programmed into all OBD2 PCM's (96-01).

The following are the fuel injection modes of operation, I've also added the applicable PCM Mode next to each.

Ignition switch ON
† Engine start-up (crank) Open Loop
† Engine warm-up Open Loop
† Engine start-up (crank) Open Loop
† Engine warm-up Open Loop
† Idle With engine at normal operating temperature Open Loop
† Cruise With engine at normal operating temperature Open Loop
† Acceleration Open Loop Mode
† Deceleration Open Loop Mode
† Wide open throttle (WOT) Open Loop Mode
† Ignition switch OFF

The only sensor NOT monitored in open loop is the O2 sensor.

During Closed Loop modes, the PCM will monitor
the oxygen (O2S) sensors input. This input indicates
to the PCM whether or not the calculated injector
pulse width results in the ideal air-fuel ratio. This
ratio is 14.7 parts air-to-1 part fuel. By monitoring
the exhaust oxygen content through the O2S sensor,
the PCM can fine tune the injector pulse width. This
is done to achieve optimum fuel economy combined
with low emission engine performance.


Now do you understand why the proper t-stat is critical to proper engine performance? Without reaching 195 Deg you're wasting gas, probably won't pass an emissions test, and shorting the life of your catalytic converter.

djb383

Where does it say that 195F must be reached in order for the system to go closed? How do you explain the ECM sending a "closed loop" signal well before 195F is reached? You can clearly see in the second pic that the system has gone into "closed loop" and water temp (WT) is only 94F.

SeriousOffroad

The FSM. Want a copy?

Abovetimberline

next time you start your jeep and it goes into closed loop before it reaches normal operating temp,I am curious if it will switch back to open once you start to drive it,like in cruise.

djb383

Just took this pic and as you can see the system is in "closed" loop at 65 mph at 159F coolant temp doing 19 mpg. The only time the system went momentarily into "open" loop is when I hammered the throttle.......as soon as I backed off the throttle, the info from the O2s is being used and the loop is once again "closed".

Abovetimberline

Cannot dispute what the scan guage says,the reason I asked is because until you reach normal operating temp it will remain in open loop,it will be in closed loop at idle once o2 sensor reaches 600 degrees or starts to produce voltage.

djb383

Again, what/where does it say that normal operating temp, or 195F coolant temp, MUST be obtained BEFORE the system will go into "closed" loop. I do see where it says (in the above posts) the system IS IN "closed" loop at normal operating temp......it should be, right?