Savio

So I’m somewhat new to jeeps. Have had mine for close to a year and have been slowly upgrading parts etc. well my motor lost compression and died so I have now a fresh remanufactured one. It drives great. But my questions are about my idle. It seems kinda high? But idk if it’s high or normal.

In park and neutral it idles at 1000 cold and hot. in drive it idles at 700ish. It doesn’t smell rich. Drives and runs great. Occasionally when driving for like an hour it might drop to like 800 in park. But 95% of the time it says at 1000 in park.
I replaced the tps, cleaned the throttle body, and cleaned the iac
Operating temp is between 180-200. Usually closer to 180.
sorry for the long story. But that’s the info. So I’d that idle high? Or normal.

cruiser54

Temp is low. Get a Mopar thermostat in there.

BlueRidgeMark

That's high. Correct the temp and then see where you are.

Savio

So is it just my motor trying to get to operating temp? But the thermostat is rated for 180? Which is weird cause it’s the same thermostat I used in my last motor and that one idled fine.

Spencer_P

Thermostat should be rated at 195

00t444e

180 degree thermostat is fine to use, I believe some XJs with the towing package came with a 180* thermostat. I run a 180 and it works fine, I wouldn't go any lower than that.

cruiser54

All came with 195* stats. 83501426xx.

BlueRidgeMark

*sigh* The old wive's tale, a 180 * thermostat will make your engine run at 180*.

No, it will just take longer to reach operating temperature. Contrary to popular opinion, the thermostat does not control the operating temperature. It influences it. It does NOT operate like the thermostat in your home. The operating temperature of a vehicles engine is determined by a complex dance of many factors, of which the thermostat is only one.

97grand4.0

IMHO a 180 stat will open at 180 and therefore you will run not hotter than 180, if your radiator etc is working properly.

BlueRidgeMark

It's not a matter of opinion, it's a matter of understating how automotive cooling systems work. Few people do, especially on automotive forums.

The thermostat does not set the operating temperature. That's a simplistic view that does not take into account many factors of which most people are unaware.

Consider that the stock thermostat is 195, yet Cherokees typically run at 210.

97grand4.0

Thanks, this is an interesting question. But before we get into this discussion, which I think we have had before, I make full disclosure that I have an engineering degree, and thus specific work on Control Systems and Digital Control Systems.
The cooling system is actually a " controlled system" from an engineering point of view. A control system uses, or feeds back via the 'feedback loop' , the output into the input, to again affect the output. Its engineered to have the input temperature affect, or control, the output temperature, just as your simple thermostat in your living room does. The output may exceed, or 'overshoot' or 'undershoot' the desired range, in which case that overshoot or undershoot is fed back into the input and changes the output, Its this system of a feedback loop that controls the output. This terminology is the same when we talk about the engine management system being in 'closed loop', meaning it is taking output data onto the 'feedback loop' (proper term) to the input and thus modifying the output.
Back in the days before clutch cooling fans and electrical cooling fans, the Tstat was in fact the only means of control in the system. Control in the sense that the output temperature is fed back to the input, to control the output temperature. No other component under the hood used a feedback loop to control the temperature of the cooling system, not the radiator, coolant, ...fan shroud, etc. The thermostat is the only 'active' control on the old school system.

The simplistic view of the FSM for a 98zj states, "A pellet type thermostat controls the operating temperature of the engine, by controlling the amount of coolant flow to the radiator. On all engines, the thermostat is closed below 195F. Above this temperature, coolant is allowed to flow into the radiator. This provides quick engine warm up, and overall temperature control."

OVRL4NDXJ

X2

More simply the thermostat allows the coolant to reach a certain temperature instead of preventing it from surpassing that temperature. In other words your engine may run hotter than the thermostat degree you use but won’t run cooler.

When I had a 160 degree thermostat in mine it ran cool enough for me to notice it wasn’t warming up to where I thought it should and I had it replaced with a 195 degree thermostat.

During that time mine never had the high idle problem the OP has described even at 160 degrees.

Now mine runs at exactly 195 degrees in all conditions so far if you look at it as an average.

I don’t know why some people’s run at 210 degrees and cannot comment on that.

Eric

BlueRidgeMark

In other words, the thermostat sets the MINIMUM operating temperature.

If you make short runs, a lower T-stat will result in a cooler engine, but once it's fully open, it's fully open. It is no longer controlling anything. The coolant temp will rise to where there is a balance between heat in and heat out.


It's not "some people". That is very much the norm!

Savio

Update: I just replaced the thermostat. Old thermostat was stuck open ... which explains why it a was so low (it was a 195). I replaced with the a 195 super stant. Burped it and when for a spin. Drives fine. Temp stays between 190-210. But the high idle in park is still there. When warmed up in park it stays at 1000. At 1100 I hear A slight whistle that I can’t find. I’ve sprayed every hose! It’s so annoying. In drive it idles at the line under the 1000 (what is that 700?)

97grand4.0

Sounds like the IAC motor.