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Temp gauge way off?

brtb

NAXJA Forum User
Location
Orlando, FL
Finally got around to switching temp senders last night (after the lights->gauges conversion)... and the temp gauge is just wrong.

Cold start after sitting overnight it immediately jumps to right below 210, after idling/heating up for a while it's just past the 0. Of course, when the Jeep's off it doesn't drop to zero, more like halfway past 100... Any adjustment on the gauge?

Or, failing that, any normal voltage numbers I can check the temp sender with to make sure that part of the circuit's working right?
 
Where did you get the new sender?

Jeep reversed the polarity on the gauges in 1991. I don't remember which was which, I always have to look it up. Let's say that for the '88 cold is zero ohms and hot is 88 ohms. The '91 would be 104 ohms cold and zero ohms hot. Obviously, using the sender from the wrong range of years would make the gauge read backwards. That's what I think has happened to you.
 
Got it at Advance... I don't think it's _backwards_, like one of the newer sensors would be, just reading way too high. It climbs up slowly like you'd expect, it's just skewed.
 
brtb said:
I don't think it's _backwards_, like one of the newer sensors would be, just reading way too high. It climbs up slowly like you'd expect, it's just skewed.
Huh?

What you wrote before sure sounds backwards -- starts at 210 cold and goes to zero when hot:
Cold start after sitting overnight it immediately jumps to right below 210, after idling/heating up for a while it's just past the 0.
 
Oops, sorry about that... that wasn't very clear... don't think I was very awake when I wrote that. :D

Cold start the needle's somewhere in between 100 and 210, usually about 2/3 of the way through that range. After warming up for a while it's a bit to the right of the '0' digit in 210 - in between 210 and the red zone. So it's doing a normal temperature progression just skewed +40-50 degrees or so.
 
Okay --

Is it constantly beyond 220, or does it fluctuate? The normal operating temperayure is 210, so it should hang right around there but it will go up and down a few degrees as the thermostat opens and closes. If it stays around 210-215 when the vehicle is moving but gets hotter when you're stopped in traffic or at a light, the usual culprit is the viscous fan clutch.

Also, most XJs have an electric auxiliary fan that's set to turn on at about 217 degrees. How this fan is controlled depends on what year XJ you have, but they all use a relay. If the relay goes bad and the aux fan won't turn on, that can cause problems.

Further, if the overheating is mostly on the highway, check the lower radiator hose. That's the suction side. The hose should have a wire spring inside. If there's no spring, at higher speeds the suction can collapse the hose, which blocks all coolant flow through the radiator.
 
Actually forget all that. The gauge is working now.... bad part is i didn't realize it until I red-zoned the thing on Fla. Turnpike (probably due to lack of lower-hose spring, knew I should have listened to you guys when I replaced that... of course the old hose didn't have one either) and i'm 90% sure I blew the head gasket. :bawl: :bawl:

thing starts acting weird, i pull into a parking lot, it shuts off, the steam billows out, the whole thing. doesn't seem to be seized, it still cranks. only cranked it one or two revs just in case.

No water in the oil as far as I can tell from the dipstick / peering into the valve cover, but there's some telltale signs of water dripping out right between the head and the block, so......

blah. go me. break out the pb blaster, i'm gonna need it.
:hang:
 
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Actually, cancel that too. gotta love intermittent weird failures... it's _almost_ working but acting like it's not sensitive enough.

to try to help anybody on future searches, I did manage to find some resistance values for the gauge temperature sender on an '88:

1600 ohms = 100 degrees F
309 ohms = 180 degrees F
113 ohms = 240 degrees F

For now I'll probably ghetto-rig my DMM into the temp-sender circuit so I can keep an eye on things...
 
brtb said:
Actually, cancel that too. gotta love intermittent weird failures... it's _almost_ working but acting like it's not sensitive enough.

to try to help anybody on future searches, I did manage to find some resistance values for the gauge temperature sender on an '88:

1600 ohms = 100 degrees F
309 ohms = 180 degrees F
113 ohms = 240 degrees F

For now I'll probably ghetto-rig my DMM into the temp-sender circuit so I can keep an eye on things...
NO!

Wrong values. Those are the values for the temp sensor in the block that feeds the ECU. The gauge sender is in the head. Values range from 0 to 88 ohms.
 
Well then something's wrong, because those are the values I got from alldata on the circuit diagram for the gauge, and are pretty close to what I was getting from the sender I just put in. maybe alldata and Advance are working off the same wrong data...
 
That would go a long way to explaining why your gauge is wacky. I got the 88 ohms from the 1988 factory service manual. All the gauges -- oil pressure, fuel level, and temp -- for the years 1984 thru 1990 operate on a range of 0 to 88 ohms.
 
Well then... that would make a lot of sense. I couldn't find the right values in the Chrysler '88 FSM but I might have just been looking in the wrong place... guess I'll get a dealer temp sender when I grab the tstat and radiator hose.

Thanks!
 
Just remember that you have two temperature senders. Be sure to buy the one for the instrument panel, not the one for the ECU. (I don't even know if they have the same thread -- guess I¿ll have to take a look some day.)
 
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