new xj, old issues

[hotrod39]

1990 cherokee limited, all original. my problem is heat on defrost is good, then dwindles after driving a bit, rev the motor and it comes back again, but dwindles eventually. on the vent setting it stay more consistent but is just warm, borderline cool. on the heat setting, it will blow warm on the floor for a short period(minutes), then go cold and wont come back to warm.your gues is probably better than mine.

idles at 1k rpm consistently, every now and then it will drop to the 700 its supposed to be at. any leads will help. gas mileage is terrible, i assume this is why.

bought it 4 weeks ago, i've raplaced:
belt, plus, wires, cap&rotor, waterpump and thermostat

[fredjacksonsan]

Sounds like your thermostat may not be closing all the way, or might be opening too early, and this is keeping the system too cool. It may get warmer if you sit and idle for awhile - does it?

Where is your temperature gauge while all this is happening? Most XJ's run about 210 or so (middle of the gauge). If the temp is a lot lower or is fluctuating towards the low side that would be a solid indication.

The only other thing I can think of is something under the dash is changing for some reason; hopefully an underdash guy will come along shortly.

[citizen@large]

That was quik Fred... x2 on the 'stat check.

[fredjacksonsan]

Originally Posted by citizen@large

That was quik Fred... x2 on the 'stat check.

Hey, when I'm here, I'm here .....when I'm not, I'm WAY not.

[hotrod39]

seems like it fluctuates at 190-200. after it sits at idle in the morning it cools more when i start driving(for obvious reason), i can change the thermostat this weekend and see. i asked for a thermostat for this year jeep when i replaced it a couple weeks ago

[restrorob]

Originally Posted by hotrod39

my problem is heat on defrost is good, then dwindles after driving a bit, rev the motor and it comes back again

Sounds more like a vacuum leak to me, These functions (different settings) are performed with engine vacuum. You may have a leaking vac. hose under the hood or dash or it could be the valve on the dash control assembly or possibly a pin hole in the vacuum motor (vac. diaphragm canister operating the ac/heat trap door under the dash).

Sitting idle you should have around 20" of engine vacuum (enough to keep up with a small leak) once you push the gas to take off/get up to speed the engine vac. drops to a point. Rev the motor and on the way back down to the original rpm the vac. will rise back up then settle back down to the lower level.

This would account for the hot/cool operation during RPM changes and poor fuel mileage.

Hope I didn't loose you along the way.....

[hotrod39]

changed the thermostat, same deal, its been 20+or-10 degrees out for a couple weeks, no garage so i guess it will have to wait till the weather breaks, man, i need a garage

[citizen@large]

You aint the only one rod.