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Temp Gauge Spike?

N

nwcherokee

NAXJA Forum User
Location
Bremerton, WA
Hey Guys,

I have a question about my temp. gauge. When starting from cold, as it warms up while driving, it slowly works its way up towards the 195 mark, then it will keep climbing up to about 220 - 225 for only a few seconds, then it suddenly drops way back down to about 130 until it reaches about 185 where it usually stays. I'm wondering why it spikes & then drops suddenly? It doesn't overheat at all. The aux. fan kicks in at about 220. I wired it up to where I can manually turn on the fan & it still has the ability to kick on when it's supposed to if i'm not paying attention. Anybody else experienced this? Just wondering before I spend $15 on a new sending unit to see if it fixes it. Oh yea, it's a 91, 4.0, auto, 4-door, if it matters.
Thanks
 
Hmmm...

Shouldn't see such a large indicated swing, IMHO.

Pull the gauge sending unit from the head and clean the threads, single wire sending units/sensors ground through the units body and non-conductive sealers can screw with the readings.

You could have an air pocket in the coolant system. Tighten all of your clamps--all of them. When was the last time you changed the radiator cap? Life on those is two years, your cap could be sucking air in on the cool-down cycle.

Last, I would pull the thermostat and test it with a thermometer in a pan of water for correct opening temperature.
 
The swing is too wide and you're a bit low for constant temp.

You could verify this with an infrared point and shoot thermometer pointed directly at the thermostat housing.

A new cap and thermostat is never a bad idea, especially if it's been a while. I buy my stats from Jeep and also like the Stant SuperStat. 195 degree.

If above doesn't do it, then spring for the new sending unit.............
 
Joe - I just did a full coolant flush about 5 months ago. I'm pretty sure the cap is in good working condition. If I crack it loose, I get the gulp in the overflow tank. I will check the hose clamps, but i'm pretty sure all are tight. I'm not getting a single drop green stuff anywhere. Also, I couldn't tell you how old the T-stat is. I've only had the Jeep for about a year now. It's got 157k on the ticker now, so I've slowly been going thru things fixing them one at a time. Next up on the list is water pump, T-stat & housing, temp sending unit, coolant temp sensor, drive belt & upper control arm bushings. I'm not gonna worry about cleaning off the threads & such as I will just replace the sensor. At $9 new, I figure what the hay...

Birch - I only figured the low constant temp (about 180° on the gauge) is because of the cold temps this winter. In the summer or when i'm on the trail idling & rolling slow the temp stays right around 195° - 210°. I put a piece of cardboard on the pass. side of the radiator with a 2" hole in the center, to speed up the warm up time during the winter. Not helping much. I should probably block the whole thing with only a few small holes.

Anyway, I think I will go ahead with the parts replacement mentioned above & see what that does. I'm not really concerned about it. Just wondering if anybody else experienced it. I'm more bothered by the 10 second crank time it takes to fire her up.

Thanks for the input, NAXJA is Awesome!
 
I had a similar issue. although my temps were not the same. The only thing was wan't semi-new was my cap so I replaced that. It turns out that I haven't has the issue ever since i replaced the cap.
 
XJwheelman said:
I had a similar issue. although my temps were not the same. The only thing was wan't semi-new was my cap so I replaced that. It turns out that I haven't has the issue ever since i replaced the cap.
Click to expand...

is there a good source for the cap? I might as well replace mine, my temp gauge fluctuates, plus i plan on doing a t-stat and coolant flush
 
nwcherokee said:
Joe - I just did a full coolant flush about 5 months ago. I'm pretty sure the cap is in good working condition. If I crack it loose, I get the gulp in the overflow tank. I will check the hose clamps, but i'm pretty sure all are tight. I'm not getting a single drop green stuff anywhere. Also, I couldn't tell you how old the T-stat is. I've only had the Jeep for about a year now. It's got 157k on the ticker now, so I've slowly been going thru things fixing them one at a time. Next up on the list is water pump, T-stat & housing, temp sending unit, coolant temp sensor, drive belt & upper control arm bushings. I'm not gonna worry about cleaning off the threads & such as I will just replace the sensor. At $9 new, I figure what the hay...

Birch - I only figured the low constant temp (about 180° on the gauge) is because of the cold temps this winter. In the summer or when i'm on the trail idling & rolling slow the temp stays right around 195° - 210°. I put a piece of cardboard on the pass. side of the radiator with a 2" hole in the center, to speed up the warm up time during the winter. Not helping much. I should probably block the whole thing with only a few small holes.

Anyway, I think I will go ahead with the parts replacement mentioned above & see what that does. I'm not really concerned about it. Just wondering if anybody else experienced it. I'm more bothered by the 10 second crank time it takes to fire her up.

Thanks for the input, NAXJA is Awesome!
Click to expand...

Was the flush with a radiator CLEANER, the kind you put in and drive for 3-6 hours? If it was a 15-minute flush I wouldn't put much (if any) faith in it. Prestone and Zerex and others make the radiator CLEANERS.
 
I got my cap from Advanced Auto. Its a small upgraded cap to, it has a tab on top that you need to lift up so you can twist the cap off. It also lifts the plunger up to release some of the pressure.
 
You need a new thermostat and a new radiator cap. The thermostat is getting lazy and allowing the large swing in temps. Don't get a radiator cap with the pressure release valve on it.

At minus 20* my XJ shows 200* engine temp on the dashboard gauge.
 
Tim_MN said:
You need a new thermostat and a new radiator cap. The thermostat is getting lazy and allowing the large swing in temps. Don't get a radiator cap with the pressure release valve on it.

At minus 20* my XJ shows 200* engine temp on the dashboard gauge.
Click to expand...

Agree.
 
Tim_MN said:
The thermostat is getting lazy and allowing the large swing in temps. Don't get a radiator cap with the pressure release valve on it.
Click to expand...

i replaced my thermostat and it now sits steady at just below the 210 mark. no fluctuating at all like before.

still looking for a cap. every auto parts store around here has a 13psi, not a 16psi.
 
Try a REAL parts store, not the chain stores (Duh, ain't on the screen, ain't got it man.)
 
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