Temp & Idle oddity

[packmule1911]

Normal state:
Idle = 695
Oil pressure = 35 to 55 dependling on RPM
Temp = 195

Something that's started happening and becoming more frequent:
Idle = 750-ish
Oil pressure = Normal
Temp = 140-ish

The idle change is like what happens when the A/C clutch kicks on, but I haven't hard the A/C on when this happens. The electric fan has always kicked on at around 220 as expected, but the ambient temp and driving conditions aren't getting the temp up that high these days.

Appreciate your feedback on what might be going on.

[4.3LXJ]

Better check that tstat and temp sensor. The temp gauge is completely electronic, so you could have either item malfunctioning. I would start with the tstat

[packmule1911]

Better check that tstat and temp sensor. The temp gauge is completely electronic, so you could have either item malfunctioning. I would start with the tstat

Replaced the tstat 6 a few months back, but not the sensor. Either could behave in a way that would change the readout and the idle speed?

I have either a 195 or 180 degree tstat available where I shop. Given the option, would one have an advantage over the other? I know 195 is standard.

[4.3LXJ]

The ECM thinks the engine is cold, so the idle is bumped up. Probably running rich too. The only way to really verify which one is screwed up is to actually measure the coolant coming out of the engine

[packmule1911]

Good coupon available today, so I'll just replace it all.

180 or 195 degree? Been hearing more people saying "a cooler engine is a happier engine", so since I have a choice, I'm asking.

[4.3LXJ]

I think 195 is the way to go.

[packmule1911]

Short on time last night and just addressed the sensor. Seems to have solved the problem.

One thing that's always confused me about the aux fan: stop for gas, temp about 210, no aux fan, start the vehicle after filling up, aux fan kicks on. Don't most aux fans run even when the vehicle is off? Wish mine did so.

[4.3LXJ]

Not all, it depends on how the factory set them up

[OldFaurt]

Normal state:
Idle = 695
Oil pressure = 35 to 55 dependling on RPM
Temp = 195

Something that's started happening and becoming more frequent:
Idle = 750-ish
Oil pressure = Normal
Temp = 140-ish

The idle change is like what happens when the A/C clutch kicks on, but I haven't hard the A/C on when this happens. The electric fan has always kicked on at around 220 as expected, but the ambient temp and driving conditions aren't getting the temp up that high these days.

Appreciate your feedback on what might be going on.

Sounds like your O2 sensor is going south. The engine uses that to make sure the fuel air is about 14:1 if they get weak they show lean and the ECU increases (makes rich) the fuel air mixture. This will cool the overall combustion temp and will build up carbon on the end of your tail pipe! Also running rich tends to increase idle. As rich I believe is shown by a higher voltage from the O2 sensor, it may just be the wire got too close to the exhaust and may be shorted out! Tell me how it goes!

[bruggz351]

Sounds like your O2 sensor is going south. The engine uses that to make sure the fuel air is about 14:1 if they get weak they show lean and the ECU increases (makes rich) the fuel air mixture. This will cool the overall combustion temp and will build up carbon on the end of your tail pipe! Also running rich tends to increase idle. As rich I believe is shown by a higher voltage from the O2 sensor, it may just be the wire got too close to the exhaust and may be shorted out! Tell me how it goes!

:happy0089:

[packmule1911]

It seems fine after the temp sensor repair. Keeping an eye one it. Going to take a look at the tailpipe. I imagine it will be coated with black soot if it's building up with carbon.

[GoneWithTheWind]

:happy0089:

Changed mine a few weeks ago, should have been changed years ago. Runs much better now, a lot smoother idle.

[GoneWithTheWind]

Sounds like your O2 sensor is going south. The engine uses that to make sure the fuel air is about 14:1 if they get weak they show lean and the ECU increases (makes rich) the fuel air mixture. This will cool the overall combustion temp and will build up carbon on the end of your tail pipe! Also running rich tends to increase idle. As rich I believe is shown by a higher voltage from the O2 sensor, it may just be the wire got too close to the exhaust and may be shorted out! Tell me how it goes!

Thanks.

[packmule1911]

Changed mine a few weeks ago, should have been changed years ago. Runs much better now, a lot smoother idle.
Guess I'll give it a go. They don't cost much. There's only one in the XJ?

[GoneWithTheWind]

Yes just one, it's in the exhaust pipe near the manifold. Mine cost $125.00, but it made a big difference.

[packmule1911]

I have two. One on each segment of the manifold before they merge and travel down and ou the back. Both look like a pain to unplug.

I'm using I need to replace both?