Good evening all. I have appeared here before with a erratic temp gauge. After confirming that the engine block is not plugged, having a new correct flow water pump installed, a recent radiator, new thermostat, twice this week, and this evening a new temp sending unit, my gauge still will not sit at 210. The old sending unit was corroded, and fell apart when I removed it. I knew it was bad. The gauge used to flucuate between 210 and 260. Up and down constantly. Now it goes up and down between 210 and 235. When I first start it and let it warm up, it hangs around 210, and when I start driving, it begins to move. Why.
That sounds within the normal range. My 258 runs right around there too.
The faster you go, the more heat you create and energy you use. On a hot summer day, I get borderline overheating and cap burps when I try to go over 70 mph for any extended time. That is due to my winch and lights interfering with the flow to the rad.
How's the oil level? I find mine runs a bit hotter when low a quart of oil or when in need of a change.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Hi Mike, Well I just changed the oil. And It starts moving on me while sitting in the drive way. But it takes a few minutes. I also had the head gasket done about a month ago. It hovers around 210, but slowly goes up to 235, 240 or so and then comes back down. It doesn't over heat. My heat works great. I drive 40 miles to work one way in it. I have 31 inch tires. When I arrive at work I notice no sounds related to overheating like hissing or burping. Would the temp fluctuate up and down or could it be my gauge acting up?? It concerns me a little. My fan clutch is operating properly. I'm confused!!!!!
Thanks Greg
95 YJ 4.0 Mike Roma> That sounds within the normal range. My 258 runs right around there > too.
What model is it? I had a similar problem on my '77 Cherokee (195 degree thermostat). In town, summer or winter, A/C or not, gauge read at the lower end of the green zone (195 or so). At higher speeds, it would run higher. In summer, with the A/C on and driving on the freeway, it would run near the end of the green range (but not actually overheat). It didn't used to get that hot unless I was towing down a crowded highway in hot midday sun. I replaced the radiator with an identical Modine (stock), when the old one finally quit. Same song, second verse. When that one quit last summer, I did the obvious fix-a radiator with one more row of tubes (from three rows to four-doubles cooling capacity-it's a direct square relationship). Still runs hotter at high speed (the engine has to work harder), but only slightly. Problem solved, and -DUH- it finally dawned on me-it was made for the then national speed limit of 55 mph (and the radiator size was not increased when full-time-four-wheel-drive (Quadratrac) was introduced back in the '70's (it has no two-wheel-drive capability at all). At 65-70+, ram air is no longer sufficient for the extra load placed on any engine, and more cooling is required. But I do now have a piece of cardboard covering about half the radiator during cold weather to help it heat up better. Especially since it's only a
6-minute drive to work. An oversized radiator would definitely hold your temperature down. Hope this helps.
These gauges are usually of the bimetallic strip type. There is a mini voltage regulator somewhere in the dash panel, that feeds them the correct voltage. Ones I have seen look a little like a shrunken turn signal flasher. The regulator itself could be the culprit, or it could be bad voltage or ground to the instrument panel.
It can't, unless the thermostat is having an odd sticking problem (possible). Actually, that's a more likely cause than the sending unit. It would go something like this (I once had thermostat that would stick, then suddenly open and work properly until the next cold start, on a '65 Scout): The thermostat sticks causing the gauge to rise, then suddenly springs open. The gauge now falls as the coolant suddenly begins circulating through the radiator. Since it's cool weather, the thermostat closes again and again sticks shut until it gets hot enough to again break loose and pop open, beginning the cycle again. Are you sure the thermostat was actually replaced? And, also, are you sure the thermostat is not installed incorrectly, causing it to warp slightly? Is the thermostat housing cover itself warped from uneven bolt torque?
A defective sending unit, however isn't impossible. I once went through 4 defective oil pressure sending units (not all from the same parts house but all apparently all were from the same manufacturer) and no two gave identical readings. Which makes me think-check for an intermittent partial short to the block, frame, or body on the sending unit wire itself. Grounding the sending unit lead will cause the oil pressure gauge to peg out (harmlessly). As you've said nothing about other gauges, I'm assuming they are performing normally. If they are also involved, it could be the CVR (usually built into the temperature gauge). On vehicles so equipped, it maintains a constant 3.6 volts (or something like that) to all the gauges except the ammeter or voltmeter.
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