258 Running Too Cold? 🤔 - JeepForum.com
 
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post #1 of 13 Old 08-02-2021, 04:13 PM Thread Starter
JeepinGeo
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258 Running Too Cold? 🤔

Now I have read other forums about this topic. Most of what I've seen says 195-210° is normal operating temperature for a 258.

1979 CJ5 258. The radiator is a new standard aluminum 3 row. The fan is a mechanical 7 blade. It has the original shroud. The water pump is new. I run 50/50 Prestone. The thermostat is 180° stainless steel. I live in Central Florida. It gets hot and humid in the summer, and cold and dry in the winter. Since installation of the new parts, the gauge reads ~180° constant from 0 mph up to max speed (~65 mph) on any given day, cold or hot out. At idle it "might" get up to 190°. Can't seem to get it any hotter than that, no matter if I'm lugging it down a long trail or on a highway cruise. Engine appears to run great. Just not sure why the temperature remains so low. Would yall say the engine run too cold?

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post #2 of 13 Old 08-02-2021, 04:33 PM
CrustySprings
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Sounds about like my '85 CJ 7 with the 258. A 180 degree thermostat is fine.

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post #3 of 13 Old 08-02-2021, 04:45 PM
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Sounds like it's running as you built it. Assuming everything else works (which it does from your post) it's not really going to get any hotter than the 180 cause as soon as it reaches the thermostat temp it's going to transfer the water out of the block. I've heard of people putting in 180 degree thermostats. If I remember correctly 195 degree is stock but I'm not sure how much difference there is really going to be performance wise. I suppose you might get slightly (negligible) better gas mileage out of the 195...but i'm not sure you'd notice the difference.

If it runs fine I'd leave it ... if it bothers you the next time you're in there change it out for a 195. I don't think it's worth tearing it all apart for just that.

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post #4 of 13 Old 08-02-2021, 04:50 PM
gutthans
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Gauge may be off a little, but you are nowhere near too cold. If you can't get enough heat in January, then consider a 195*. If it drops into the 160 range, then maybe you have a fail-open type of stat and it would be prudent to replace it.
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post #5 of 13 Old 08-02-2021, 05:45 PM Thread Starter
JeepinGeo
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I will leave it be in that case. Just wanted some insight. Thanks for the feedback guys.
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post #6 of 13 Old 08-02-2021, 07:30 PM
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If you run a 258 AMC engine it was designed to run with a thermostat that started to open at 195F and was fully open at 218F.

You have proven that your engine is not at risk of overheating, left to itself with no thermostat it would rarely even approach 195F.

The engine is designed to operate at 195F, the tolerances are fixed for this amount of thermal expansion and the emissions are measured at this. When I had $10 and 30 minutes I would IMHO change to the correct thermostat.

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post #7 of 13 Old 08-03-2021, 01:17 AM
mudbfun
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The fact that you dont get any hotter then 180* just means that your 3 core radiator and 7 blade fan with shroud are plenty efficient for your configuration. Understand that is the same setup that is used for many heavy duty trucks with a V-8 for towing applications. You could put in a hotter T-stat or run it just the way it is. Personally I don't think the motor is going to care either way.
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post #8 of 13 Old 08-03-2021, 02:54 AM
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Quote:
Originally Posted by BagusJeep View Post
If you run a 258 AMC engine it was designed to run with a thermostat that started to open at 195F and was fully open at 218F.

You have proven that your engine is not at risk of overheating, left to itself with no thermostat it would rarely even approach 195F.

The engine is designed to operate at 195F, the tolerances are fixed for this amount of thermal expansion and the emissions are measured at this. When I had $10 and 30 minutes I would IMHO change to the correct thermostat.
I think you're giving those engineers from the 70s and 80s a little too much credit. A 195* is safe regarding engine heat and warm enough to run the heater and that's about it.

If I were going to change anything here, it would be that 7-blade fan. I'd run a non-thermal clutch and a 5-blade but that's just splitting hairs. Hey, it's nice to have a CJ on here that's not over-heating for once


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post #9 of 13 Old 08-03-2021, 04:31 AM
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Quote:
Originally Posted by Shawn Watson View Post
I think you're giving those engineers from the 70s and 80s a little too much credit. A 195* is safe regarding engine heat and warm enough to run the heater and that's about it.

If I were going to change anything here, it would be that 7-blade fan. I'd run a non-thermal clutch and a 5-blade but that's just splitting hairs. Hey, it's nice to have a CJ on here that's not over-heating for once


Shawn
Engines, back to the 40s and 50s were designed for specific temperature ranges--the tanks and planes of WWII did not ignore the effects of temperature. To some degree for clearances and to some degree for efficiency (hotter is usually a bit more efficient, as long as it doesn't get hot enough to do mechanical damage), and even for cooling--a hot radiator sheds more heat than a cold one.

The 4.2 and 4.0 should be running 195-210 typically, and running a 195 year round will NOT cause overheat problems. If an engine is overheating with 195, then there are other cooling system issues.

I have had a couple of failures with 'failsafe' thermostats. At some point the 'fail safe' activates and the thermostat sticks open (not terrible, but not what you want).

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post #10 of 13 Old 08-03-2021, 06:18 AM
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I looked it up in the 74 TSM. It says 205* for a 258 and 232, and 195* for the 304. If the OP lived in a colder region I'd say change it.

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post #11 of 13 Old 08-03-2021, 06:27 AM
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Maybe this will help
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bender.jpg  

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post #12 of 13 Old 08-03-2021, 06:31 AM
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What temperature does "cold boiling" occur?

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post #13 of 13 Old 08-03-2021, 10:25 AM
LumpyGrits
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You want a 195* t'stat.
Your engine will thank you!
Gary

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