Get rid of the thermostat for the summer?

[SecondMonkey]

I have a Jeep with the 4.0L inline 6 engine. As is very common with this engine, mine overheats every summer. Today I noticed the t-stat housing gasket was leaking so I have to take it off and replace anyway.

Any good reason I shouldn't remove the t-stat for the summer? She runs at about 210 degrees, the t-stat is 195, so it isn't doing much anyway. I know this is only a quick bandaid, but it seems like a perfect time of year to toss the stat anyway.

The real problem is I need a new radiator and fan, but I haven't gotten around to fixing that in 3 years because it only overheats in the 3 months of summer....and I don't have the time right now.

 

[GMBoy]

Fix the problem. Never run w/o a stat.

 

[Drew99GT]

Running with out a thermostat will likely make it run hotter. The thermostat restricts flow though the system so it can soak up heat.

210 with a 195 degree thermostat in summer is par for the course. If it was 250, THEN I'd be worried.

Is the electric fan coming on when it gets into the mid 210s to 220?

210 is far from overheating.

 

[glennc]

Originally Posted By: Drew99GT
Running with out a thermostat will likely make it run hotter. The thermostat restricts flow though the system so it can soak up heat.


That turns out to be a myth.

However, removing it will extend warm-ups with consequent affects on economy, possibly substantial, and perhaps engine wear.

If you don't care about those things, it might help it run cooler.

 

[brianl703]

Have you checked the fan clutch to ensure that it's not slipping excessively?

How about the radiator cap, to ensure that it's holding pressure?

 

[AcuraTech]

Sounds like a band-aid fix at best. Are you planning on keeping the Jeep for awhile? If so I would drop the coin and get it fixed right.

 

[dwendt44]

You should be able to get a 180° or even a 160° thermostat; though you may have to order it out.
You need some restriction there.
GMboy has the correct answer though.

 

[Drew99GT]

Originally Posted By: glennc
Originally Posted By: Drew99GT
Running with out a thermostat will likely make it run hotter. The thermostat restricts flow though the system so it can soak up heat.


That turns out to be a myth.

However, removing it will extend warm-ups with consequent affects on economy, possibly substantial, and perhaps engine wear.

If you don't care about those things, it might help it run cooler.


Not in my experience. Take it out and run it in 100 degree weather for the afternoon.

 

[mechtech2]

Thermostats are rated at the OPENING temperature- when they START to open.
So 210 is OK for a 195 thermostat. They are not NASA certified, anyway.
Run a thermostat for sure. A cooler one is a horrible thing to do. It reduces fuel efficiency because of the sensor telling the computer to run richer, and possibly even go to open loop.
A normal thermostat [195] keep the cyl head temp up there, so the heat of combustion does not have to keep heating the head up to a homostasis state. It can then be used to produce power.
When you need it, the thermostat will open anyway.

Some Ford/Lincoln cars have thermostats that have a bi-rating and control. They run 220 or so, and under load are programmed to go to 195 [approximate numbers].
This helps fuel efficiency .

 

[Gary Allan]

205-210 is common even when you're not in the summer heat. Removing the thermostat should not help you if you have some other defect. The rad probably has more resistance to coolant flow than the thermostat does wide open. (yes, folks, there is a pressure drop across the rad from stat outlet to wp suction)

 

[BlazerLT]

Change the rad cap.

Also, 210 is standard operating temperture so when is that "overheating"?

 

[pickled]

I don't want a "NASA Certified" component on my vehicles...those guys make the engineers at the big 3 look mighty bright at times!

 

[Ramblin Fever]

The more you forgo the actual problem, however, the more your exposing it to a bigger problem, i.e. headgasket failure if it's not cooling efficienly.

 

[Merkava_4]

Originally Posted By: Drew99GT
Running with out a thermostat will likely make it run hotter. The thermostat restricts flow though the system so it can soak up heat.


I had always thought the idea of a thermostat was to keep the coolant in one place long enough so that it could be exposed to airflow and GIVE OFF HEAT; I must be thinking backwards.

 

[swalve]

The thermostat's job is to keep the coolant at a high enough temperature. If the coolant temp is too low, it will draw too much heat off the engine and cause it to not run right and use more fuel trying to keep its temperature up.

The thermostat housing is a two way valve- when the thermostat is closed, the coolant circulates right back into the engine. When the coolant reaches a certain temperature it opens and lets the coolant flow into the radiator, and then the water pump makes that flow up with cooler water from the radiator.

The rate that heat sheds off in the radiator depends on the temperature difference between the water and the air. (among other things) The bigger the difference, the quicker the heat will move to the air. But the point is that if the engine needs to shed heat, you wouldn't want to restrict flow and keep water in the radiator because as it cools off, it will shed less heat. In the meantime, the water in the engine will be overheating. What happens is that the thermostat is a variable valve- it's not just on or off. When it's too cold, it's off. When it's too hot, it's on. But in the middle area, the 'stat adjusts its opening to maintain the desired temperature. If the water heats up one degree, the stat opens up just a little more. It continuously varies itself.

But if you're running hot, and if the stat works right, it will be wide open. The overheating problem will be caused by the engine generating too much heat, a failing water pump, or the radiator isn't shedding the amount of heat it used to.

 

[gomes512]

What model year Jeep? Manual clutch fan or electric? Are you overheating in traffic/low speeds only?

The 4.0's only overheat when the cooling system isn't taken care of. My ol '94 grand cherokee can tow a 1 ton trailer in 98 degree summer heat all day long without going past 215.

It would overheat before in slow traffic before I changed the fan clutch, easy job and hasn't acted up since. I replace the coolant in the radiator at the end of every summer with the regular ol green stuff. Still on the original water pump and thermostat at 140K and 14 yrs.

 

[brianl703]

Originally Posted By: swalve
The overheating problem will be caused by the engine generating too much heat, a failing water pump, or the radiator isn't shedding the amount of heat it used to.


Or...a radiator cap that isn't holding pressure like it's supposed to allowing the coolant to boil.

 

[Gary Allan]

Quote:
What happens is that the thermostat is a variable valve- it's not just on or off. When it's too cold, it's off. When it's too hot, it's on. But in the middle area, the 'stat adjusts its opening to maintain the desired temperature.


Not all stats react this way. Many have a narrow range between open and closed and they don't modulate well. Robert Shaw makes a good one, but it doesn't make one for every application. I can see my thermostat open and close routinely going down the road at a constant speed. The swings aren't radical (just 205-210). That means that I'm passing too much water when it's open. Actually, it's that my rad is bigger and when the engine "takes a gulp" upon the thermostat opening fully, it takes that much of a temp hit before the coolant (now too cool) reaches the thermostat. The only thing that changes with ambient temp is that the cycles change in frequency.

That said, I've never seen an engine without a thermostat overheat where the overheat wasn't because of some other issue. Not that I pretend to have "seen it all".

Cooling isn't always that simple.

 

[swalve]

I agree, I think. Part of the reason for the effect that you see is the design of the engine. Most engines, as I understand them, have the thermostat on the output or hot side of the engine. But the makeup water comes in on the cold side. So when the temps are in the range where the thermostat is cycling, it will exaggerate the cycling because there is a signal delay- by the time the thermostat sees the cooler water and starts to close, it has already "let in" too much colder water.

I'm sure having no thermostat improves flow, but what that amounts to is increasing cooling performance to more than 100%. The system was designed (hopefully) to be effective with the thermostat installed. If it was designed right, the system will do all the cooling necessary with the thermostat installed and wide open. If that's not enough, there is some other problem. Especially if it used to be enough when the car was newer.

A more perfect system would have multiple sensors and some sort of temperature map. IE, when the engine is under X% load, it needs to adjust flow so that the temperature and flow of incoming water will be the right amount to create the desired temperature at the output.