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post #1 of (permalink) Old 06-18-2004, 01:14 PM Thread Starter
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Low Engine Temp - Is this an issue?

About two weeks ago I noticed that my engine temp guage (factory style in cluster) was registering lower than I usually remember it. I drive about 40 miles each morning on the interstate and it used to be that my guage would be about dead center of the range. However lately it is only about a quarter of the way up. The engine appears to be running good and I changed the sensor and get the same reading. I think the guage is accurate and intend to take ohm readings tonight. I have also checked the connector at the sending unit to make sure it is snug. The heater blows very hot as well.

This is on an 84 CJ7 with fresh 258 and MC2100, the thermostat is a 195 degree unit. I have read the posts that say engines are designed to run at various temps for a reason.

My question: Is this a possible symptom of a problem? What to look for? Should I even care?

Thanks for your input.
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post #2 of (permalink) Old 06-18-2004, 01:44 PM
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Re: Low Engine Temp - Is this an issue?

A thermostat can get stuck open just as easy as it can get stuck closed. You should replace it. Your gas mileage and performance will improve....and in winter time it will give you warmer air from your heater.

On newer fuel injected engines the difference in mileage can be as much as 5 MPG.
post #3 of (permalink) Old 06-18-2004, 01:52 PM
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Re: Low Engine Temp - Is this an issue?

I agree with John. Sounds like a thermostat. Easiest way to find out is remove the cap (on a cold engine), start the Jeep and if coolant is circulating through the radiator on a cold engine, then the thermostat is stuck open.
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post #4 of (permalink) Old 06-18-2004, 05:34 PM
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Re: Low Engine Temp - Is this an issue?

The machine shop that did the work on my rebuild said that the main reason for problems they see on the 258 is not running hot enough. Cold water constantly hitting the No. 1 cylinder wall ends up eventually ruining it.
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post #5 of (permalink) Old 06-18-2004, 09:49 PM
 
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Re: Low Engine Temp - Is this an issue?

Iah 2420,
I was counceled to run a 160' stat in my 258 in my area where summer temps are high. Does any one know if this is good or bad advise???
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post #6 of (permalink) Old 06-19-2004, 12:46 PM
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Re: Low Engine Temp - Is this an issue?

With a 40 mile trip, I doubt that the thermostat stuck open is the problem. I'd bet on the sensor ground. I'm assuming that it is a one wire sensor so it depends on the ground to complete the circuit. Did you use a sealer on the sensor? Pipe dope, Teflon tape, silicone, etc.? All of those can insulate the sensor body from the engine. Connect a piece of wire to the sensor body at one end, you an use a hose clamp to hold the wire end to the sensor, and connect the other end to the gauge ground, one of the mounting clamp posts should provide the gauge ground. If the reading returns to normal, you'll know that there is a poor ground at either the sensor or the gauge.
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post #7 of (permalink) Old 06-22-2004, 11:47 PM
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Re: Low Engine Temp - Is this an issue?

I run a 160 in my 4.0 YJ. I have a lot more power and passes smog (<~~~most important!).

Mongo [img]images/graemlins/givemebeer.gif[/img]
post #8 of (permalink) Old 06-23-2004, 04:47 AM
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Re: Low Engine Temp - Is this an issue?

Put a 190 in the 4.0. Your engine won't run any cooler with the 160. It only affects the warming up time, meaning it will take a long time before your engine reaches proper operating temp. With the 160 it'll wear faster, run poorer and richer thus bringing down MPG and clogs up your cat. Your dipstick probably looks like it's put into mayonaise (I mean your Jeep's [img]images/graemlins/grin.gif[/img]) unless you drive real distances. Temp wise you can't compare the 4.0 and 258. The 4.0 is designed to run quite hot (200-220).
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post #9 of (permalink) Old 06-23-2004, 05:03 AM
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Re: Low Engine Temp - Is this an issue?

Not knowing the 258, I can say a 160 T/stat opens quite quickly so operating temp is not reached as fast as possible. Not knowing the operating temp of a 258 I think the thermostat should open about 10 degrees lower than operating temp for shortest warming-up time. Outside temp should'nt affect your choice for a T/stat. High outside temp only means operating temp is reached fast. Good for the engine. When operating temp is reached, the T/stat begins to open en starts cooling to prevent overheating.
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