Thermostat questions and running RPM and temps

JLANEF

JLANEF

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Jan 9, 2019
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Chandler Arizona
I have a 1999 in Arizona. I have recently flushed the radiator and replaced the coolant. I have recently upgraded to 4:10s & 35inch tires with a 4.0 and automatic. Some questions on temp and thermostat.

Right now it runs around 190 running to the store and such. Out on the highway running 60 (2400 rpm), it will heat up to 220 - 230 in 5 to 10 minutes. trail running at low speeds, it runs 210+. I am going to check and see if it even has a thermostat in it. But regardless I am going to put in a new one. Questions?

What temp thermostat for Az?

What is a comfortable highway RPM for running on the interstate to trails in Az heat and a good condition 4.0 motor, but 130,000 miles.

I still have the stock speedometer gear in and use a gps. At 2400/2500 I am doing 60/61 mph. But my speedometer says almost 70. It seems 70 would have been plenty fast to cruise when it was new. At 2400, that is what 90% of the drive train is running, 70 mph. It also seems like I am pushing it at that speed. But I just realized it has been in the heat with the top off and the wind blasts and such may make the “pushing it” feeling exaggerated.

I also have a winch on front so some airflow is shielded.

Thoughts on thermostat rating and comfortable interstate RPM. Also, will a newer radiator help?
 
Always use a standard 195 stat and a mopar radiator. The aftermarket rads are horrible. How does your fan clutch look? When you spin it with the engine off and hot, does it freewheel or have a lot of resistance?

Also, your use of 4.10 gears with 35's is questionable. I would not go above 33's with that gear ratio w/ the 3 speed auto, but others might disagree.
 
Arizona, Death Valley, or Minnesota the thermostat needs to have a 195 degree temperature rating and it must be a NON-failsafe model. So-called "failsafe" thermostats may not fail in the closed position but they fail way too easily and often in the open position leaving it inoperative.

210-220 is the normal temperature for the engine. And stay with the Mopar radiator, its all aluminum core and its design cools better than all but the most expensive aftermarket radiators. I wheel mostly deserts in SoCal/Arizona and will stay Mopar.

Since your speedometer isn't matching what the GPS says, it's time to recalibrate it via a new 34 tooth speedometer gear which is appropriate for 35's and 4.10 axle gearing. http://www.4x4xplor.com/speedo.html
 
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rouxbicon said:
He indicated 2400 @ 60 mph (by gps), which would be approximately 2800 @ 70 mph. Gearing seems about perfect, no?

Agreed though on the 195 deg thermostat, either Stant Superstat or Mopar
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I misread the mph to be 70 mph at 2400, yes 2400 at 60 mph would be pretty good.
 
Higher temps on the highway is a bit questionable, should be the other way around.
Only time i see anything past 212 is a long time idling under 100+ degree Florida tropics, which stabilizes around 240
 
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eastbloc said:
Higher temps on the highway is a bit questionable, should be the other way around.
Only time i see anything past 212 is a long time idling under 100+ degree Florida tropics, which stabilizes around 240
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This...

Plus let's review

Coolant level is? After having driven it a bit is it still in the good level?

In AZ I'd go no higher than 50/50 ratio.

It doesn't take much to err that and make it 70/30 or worse...(higher)

195 stat... is what you need.

If your radiator/heater core/fan are in good shape...

What you are describing is a hose sucking shut.

Years ago they had a spring inside to prevent this. The spring broke down over time and the hose would suck shut.
Today's hoses don't need a spring as the properties of said materials have improved. That said nothing lasts forever...and if you've got a hose sucking partially closed that can be enough to limit flow at higher rpm.

I echo again if everything is working good your rise in temps while driving...I'd look into your hoses. If you replace one...replace them all.

Good luck
 
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Good input! No leaks, coolant good, will check fan. Never thought to check it with everything hot. Never thought to check hoses either. They seem fine but I should squeeze them, or maybe replace both just for General Principal!

on gear ratio, I didn’t think I could go above 4:10 with the auto. 1999 is 3 speed auto with no overdrive. I live in the easy valley of Phoenix and the majority of trails are an hour away by freeway each way at least. 4:88s would make it real slow on the freeway as I just don’t want to run 3000 rpm for hours on the freeway in 100 heat with the air on!

which brings me to the last question. Is 2800 for an hour or so on the freeway at 100 degrees outside, with the air on going to be ok for the 4.0 with 130,000?
 
JLANEF said:
Good input! No leaks, coolant good, will check fan. Never thought to check it with everything hot. Never thought to check hoses either. They seem fine but I should squeeze them, or maybe replace both just for General Principal!

on gear ratio, I didn’t think I could go above 4:10 with the auto. 1999 is 3 speed auto with no overdrive. I live in the easy valley of Phoenix and the majority of trails are an hour away by freeway each way at least. 4:88s would make it real slow on the freeway as I just don’t want to run 3000 rpm for hours on the freeway in 100 heat with the air on!

which brings me to the last question. Is 2800 for an hour or so on the freeway at 100 degrees outside, with the air on going to be ok for the 4.0 with 130,000?
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4.56 is the lowest ratio I'd recommend for your 32RH and 35" tires. My previous TJ had a 5-speed with 35" tires so I regeared it to 4.88 which produced perfect highway rpms, 2700-2800 at 70-75 mph. Then I converted that 5-speed to the same 32RH automatic you're running and the 4.88 gears were a little too much for it, I ended up moving over to the slow lane and driving at 55 mph or so on the highway.
 
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Jerry Bransford said:
Arizona, Death Valley, or Minnesota the thermostat needs to have a 195 degree temperature rating and it must be a NON-failsafe model. So-called "failsafe" thermostats may not fail in the closed position but they fail way too easily and often in the open position leaving it inoperative.
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I know you don't like failsafe t-stats, but don't fully understand why. Is it because they simply fail more often? Having had both types fail on me over the years - one of each - I'd much rather have a cold running engine for a day or two than an overheated one with blown head gasket. What am I missing?
 
Zorba said:
I know you don't like failsafe t-stats, but don't fully understand why. Is it because they simply fail more often? Having had both types fail on me over the years - one of each - I'd much rather have a cold running engine for a day or two than an overheated one with blown head gasket. What am I missing?
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That in 11-12 years since my thermostat failure on the trail, I haven't had another since while running a standard Stant thermostat. I'd likely have had 2-3 failsafe thermostats hung up in the cold position by now.
 
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How freely should the fan turn buy hand? I can turn mine but it won’t even turn a couple of turns if I try and “spin” it with my hand. But it turns.

another question. Jerry confirmed what I thought that a little overfill on an automatic 32rh tranny is ok. What about oil. I noticed they overfilled my oil when they did the RMS. About 1/4 inch over max on dipstick. Should I drain it down?
 
JLANEF said:
How freely should the fan turn buy hand? I can turn mine but it won’t even turn a couple of turns if I try and “spin” it with my hand. But it turns.

another question. Jerry confirmed what I thought that a little overfill on an automatic 32rh tranny is ok. What about oil. I noticed they overfilled my oil when they did the RMS. About 1/4 inch over max on dipstick. Should I drain it down?
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If the ambient temperature inside the engine compartment is hot so will the fan's thermostat clutch which will make it difficult to turn. The fan will not continue to spin once you let go of it. It will only allow the fan to spin a bit if everything is cold.

I wouldn't worry about the 1/4" over full for the engine oil pan, that's common.
 
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JLANEF said:
I have recently flushed the radiator and replaced the coolant.
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Flushed the radiator or entire system with a good chemical flush like Thermocure? Mine was running hotter than normal at 220-225. I flushed the system twice and couldn't believe the crud that came out. It now runs at 205-210 all the time.
 
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TheBoogieman said:
Flushed the radiator or entire system with a good chemical flush like Thermocure? Mine was running hotter than normal at 220-225. I flushed the system twice and couldn't believe the crud that came out. It now runs at 205-210 all the time.
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I should do that soon, it has been a while.
 
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TheBoogieman said:
Flushed the radiator or entire system with a good chemical flush like Thermocure? Mine was running hotter than normal at 220-225. I flushed the system twice and couldn't believe the crud that came out. It now runs at 205-210 all the time.
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just radiator. Unfortunately I live in a closed community with no storm drains or anything. We don’t even have a disposal place. All in the Phoenix area charge AND REQUIRE you to live in the town of the disposal facility. Our community is officially in the county and no County disposal sites. I have checked around trying to find somewhere that I can do a proper flush, but have been unsuccessful. I guess I’ll resort to a lube place or mechanic to do it. But I figure my chances of it being done well (or even at all), are less than 50/50. When I did the radiator flush last spring it was really rusty and crap, so that is probably it.
 
TheBoogieman said:
Flushed the radiator or entire system with a good chemical flush like Thermocure? Mine was running hotter than normal at 220-225. I flushed the system twice and couldn't believe the crud that came out. It now runs at 205-210 all the time.
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Boogieman, the whole system contains about 2 1/2 gallons. drain it all and then put how much thermocre in? How much? Then flush with how much? Trying to determine how much wastefluid I would have in the end? As a kid back on the farm in Iowa I would flush at least 20 to 30 gallons through my 327 at least!
 
5632 said:
Keep in mind that at speeds over 40 fans are not necessary. So any overheating at speed is not fan related.
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I guess I didn't understand. I thought at high mph speeds is when the freewheeling fan comes into action and is pushed by the wind and actually starts spinning faster then the motor and pulling even more air through. What does the freewheeling fan do at under 40? Thanks, always good to learn more!
 
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