258 temps “normal” - JeepForum.com
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post #1 of 21 Old 02-08-2021, 02:03 PM Thread Starter
82/84 CJ7
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258 temps “normal”

Hello everyone. Hope all is well. I’m just writing to get some feedback on my conclusion here. I’m still using the stock temperature gauge (I know I know I need to change it, I’ll get to it...... eventually).

But for now I’ve just been testing what different parts of the gauge mean temp wise using a infrared gun. So driving around on streets or freeway or stays somewhere a little past the middle closer to H. My gun says that’s approximately 180* at the thermostat outlet and 180-190 at the rear most coolant hose on the intake manifold.

Now under idle sitting for awhile my gauge creeps up to just and I mean just below the H just barley still in the green zone and it freaks me out but upon further inspection with the temp gun this corresponds to only 200-205 at the thermostat outlet and 200-212 at the rearmost hose on the intake manifold. And the bottom radiator hose was only at 175-180ish but it was hard to get a reading.

So my conclusion is the temp gauge is biased to read hot and the middle is really a little cold actually and just below H is around 210ish. Are these temps to hot. The temperature gauge always comes back to the middle once I get moving again and it’s also worth noting I never actually overheat like I’ve never had it boil over or start bypassing the cap. It smells a little warm but that’s probably the oil from the valve cover leak.

Also if I chose to replace the thermostat would you all recommend 180 or 195 for my Jeep. I’ve heard a lot for both sides and I’m on the fence.


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post #2 of 21 Old 02-08-2021, 03:42 PM
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195 is the specified thermostat. 180 or 195 thermostat works fine, but don't go lower. Too low and the engine does not run efficiently. If you have a stock radiator with fan shroud .... and properly functioning mechanical fan clutch .... and its all working well, use a 195.

Most 258's that I have seen run right around 200-210 under normal conditions...that will also give you the best gas mileage.

If your engine runs too hot, the root cause is typically not the thermostat temperature rating.

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post #3 of 21 Old 02-08-2021, 03:50 PM
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My first thought would be, check the radiator cap, to make sure it is holding correct pressure @ 16 lbs. Cheap/easy start to replace it, then see how your temps run, but if you are inclined to replace thermostat, I always go with 195*......that is just me
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post #4 of 21 Old 02-08-2021, 04:10 PM
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If your winter gets much below 50*, install a 195*. If that doesn't happen often, a 180* works nicely.

My experience is that it takes a 195* or better, to maintain full use of a warm heater. A 180* is a better choice if your rig is 'cooling compromised' in the summer and around town and you can get away with slightly diminished heat. That's how I look at it....but , of course, 195* is the usual standard.
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post #5 of 21 Old 02-08-2021, 07:03 PM
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195---I am currently using speedo on the right.

It was prettier!

I've installed many gauges through the years on my previous 5 CJ-5s---a second set on the speedo on the right.

Over the years I have also thought my temp senders were bad and replaced them unnecessarily.

If you will notice they are not high dollar---but work just fine....they even moved their paint pattern during the paint process of the fuel gauge---notice the extra lines!

https://www.oconeeoffroad.com/Gauge-..._p_162882.html

I have my way to install them (using a 5 volt adapter)--John Strent has a similar method---may be more streamlined than mine

What I have found with all of my Jeeps (except my Willys) With wonderful radiators, new senders, new gauges (or old)

With a 195 degree stat at operating temperature the Temp Needle will reach the green painted line and stop----all day long! Unless you get into stressful 4x4ing it may rise to the halfway mark.

If we are getting higher, you can break out the voltmeter/ ohm meter ----remove the sender wire and check the temp sender's OHMs at operating temp------I see what mines putting out and we can compare. (providing we are both running a 195 stat)

I would suspect a higher temp reading on the highway at operating temp (with any stat, 190 or less) might mean your radiator may need some professional attention. It may still work, but a good professional cleaning may make it so much better.

I will OHM mine tomorrow.

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post #6 of 21 Old 02-08-2021, 07:07 PM
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195 is the correct one, do not use 180, it dos not make your 258 run better and in fact leads to more wear.

Your temps sound fine, still worth checking the thermostat and radiator cap and flushing the whole system.

Jeep gauges are not accurate, you just have to get used to where they normally read.

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1984 CJ7 258ci - Puthijeep
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post #7 of 21 Old 02-08-2021, 07:43 PM
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Quote:
Originally Posted by BagusJeep View Post
195 is the correct one, do not use 180, it dos not make your 258 run better and in fact leads to more wear.
I'd like the basis for that part of your statement.

I am acquainted with the fact that increased warm-up time (as in no or an open/failed thermostat) does lead to increased wear due to a number of things. However, whether a 180, or 195, or even a 210...they are all closed at start-up and require exactly the same amount of time to get to 180. You are suggesting that the motor wears more because it's not at 195? Would that same logic then apply to hold true for 210*? What about running 220*?

The last time I studied this, it was some NASCAR research examining wear and power production that had concluded that the engine performance is hindered below 145*, and that no additional performance gain was realized below 165*. They also concluded that power production and longevity was ideal between 165* and 200*. Now, admittedly, that is race research and not street. But we do know that higher temps are part of the emissions game, and that has zilch to do with best operation or wear. So, technically their research does actually conclude that a colder than 195* motor runs better, and that the range between 165* and 195* is where it all comes together.

So really, what's the basis for the comment? I'm game, because I haven't updated on this in a long time???
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post #8 of 21 Old 02-08-2021, 09:16 PM
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This is what the makers decided it should be,

I try to adhere to their standards.

Even though I have ridded my engine of many temperature controlled gadgets,

(which may have needed 195 degrees to operate).

In the AMC JEEP service manual I looked but never found a passage that offered the use of any other degree stat.

I have found that "JEEPFELLER" operates bunches more better when the heater is kicking out 195 degree air.

I'm not going off of opinions or science, just going by what the big guys "SAY"....not recommend,

Thus far, their book has not let me down.

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post #9 of 21 Old 02-09-2021, 01:54 AM
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Jeepfeller is correct, it is the manufacturers recommended temperature.

Now why is it the case? It does two things, it allows the engine to warm up more quickly and it keeps the temperature regulated. The machining of the engine is to achieve longevity and performance at that temperature. If they wanted to design it for 180, they would have. But at 195 F (90 Celcius) the hot coolant is at the right temperature, just below boiling at sea level it will even in an uncapped system circulate and give maximum heat transfer in the radiator.

By putting in a 180 you may reduce the engine temperature but it will not increase cooling capacity.

Now I have limited data on wear v temperature but I give you the following:

HANG ON< JF NOT WORKING.

Sorry, graph is not displayable at the moment. In brief the amount of cylinder wear is related to engine temperature, it is not a linear relationship so the difference between 180 and 190 is real, but not as pronounced as between say 120 and 130. This is an old study but heck, we have old engines.

BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
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post #10 of 21 Old 02-09-2021, 06:02 AM
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On cooling:
I had a good friend who worked as a mechanic in AZ. In the course of a conversation he explained that it was a common tactic to install 195 thermostats in older cars that were running hot (this was back in the early 80's when 160's and 180's were the norm). The concept was that the 195's would hold the coolant in the radiator a little longer, allowing additional cooling. He swore by the technique and I've run 195 or higher in all my rigs since with no ill effects.

Always sounded counterintuitive to me but that was the standard in the shop he worked in.

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post #11 of 21 Old 02-09-2021, 06:33 AM
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I always figured them Rambler folks who designed and built the engine had a bit more smarts and experience in this area than I have so I always use an 195* thermostat. Anyone who says different needs to prove their increased smarts and experience for me to change my mind. Bob out!

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post #12 of 21 Old 02-09-2021, 06:51 AM
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OEMs have to make sure that whatever rolls off the line is good-to-go whether it takes delivery in Alaska or Arizona. That means it can't get ripping hot in the summer and the heater has to blow hot air in the winter.

There's not a thing in the world wrong with a guy tailoring it to his specific needs/desires based on his location and usage.


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post #13 of 21 Old 02-09-2021, 08:43 AM
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And people wonder why manufactures don't put numbers on gauges...
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post #14 of 21 Old 02-09-2021, 01:46 PM Thread Starter
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Thanks everyone for the info. A lot of good points being brought up.

Jeepfeller how do I hook up the multimeter to the temp sensor to read the OHM.

As a stop gap I’ve bought a mechanical temp gauge I’m putting in one of the old computer temp sensors in the intake manifold. Just for curiosity sake. Say I am actually having temp problems I’ve always heard overheating being around 240 and 230 being ok only for short times. Is it any different on the these rigs or do 258s have a different temp range for “overheat”

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post #15 of 21 Old 02-09-2021, 08:06 PM
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Not so simple Bagus. Below is a graph illustrating what I learned and saw demonstrated about operating temps and cylinder wear. Please notice, as I commented about that the best combination of power production and least wear occurs in a zone that begins around 170* and ends around 190*. Guess what thermostat is exactly in the middle of that range?

As Shawn pointed out, mass produced vehicles have to function across a broad range of variables. The standard (default) 195* is a good compromise range for needing a hot heater output, and keeping regular driving temps close to the power band. Hotter thermostats (more popular with computer and emissions regulations) may reduce emissions, but at the expense of robbing horsepower. Colder thermostats raise the wear factor quite quickly, and below 165* you are also out of the peak power band.

First, a closed stat is a closed stat...regardless of rating. A 180 warms up exactly as fast as a 195, until it begins to open (178 -185 or so). The 195 will continue to grow hotter slightly faster than the 180 because it's still closed for a few seconds longer...but that isn't what's important to focus on.

You must consider that all stats operate over a range...not at a specific, single value. The calculated difference between incremental wear during warmup is absolutely insignificant once an operating temp of about 165 is reached, and it's a flat curve until wear accelerates somewhere around 230 or so depending upon materials and tolerances. Point being that a 180 warms just as fast as a 195 UP TO THE INTERSECTION OF THE POWER BAND AND WEAR BAND. once that zone is reached, it's not important that the 180 is beginning to flow, or that the 195 is just a few seconds from opening.

Now, consider why the recommendation is typically 195*. WINTER HEAT. Operating the heater core increases cool down. The 195 keeps the cycle range high enough that the heat draw isn't felt by occupants before closing and rising again, whereas a 180 or lower would induce a 'lack of heat' sensation every time because it won't rise high enough, for LONG ENOUGH to feel warm. It's an operational parameter, not a wear issue. The wear occurs during the warm up, not at operating temps. The 180 does NOT wear more than the 195, but it actually does keep the motor closer to peak horsepower production. But, as you should know, there are setting that manufacturers choose that have specific purposes. The 'best' isn't always what you think it is. This discussion, of course , is better suited to older motors running carburetors, non-computer ignitions, headers, and performance modifications, etc. If 'best' is emissions control, then a 195 or 210 is more likely your target. Computer controls is a whole different universe and is designed for (again) specific measurable outcomes, with target temps being calibrated to run certain things that are way beyond mere power bands and cylinder wear. (Note: this is not a scientific engineering post...just my summation of several in my own words.)
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