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Driving without thermostat...


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Hello all:

 

First the facts: '99 Legacy SUS 2.5L Auto. 142K miles.

 

The car appears to have a blown HG...(classic symptoms--bubbles in the overflow tank, oily residue, temp climing rapidly, etc.). This happened on the road a few weeks back, and the service station mechanic removed the termostat. No overheating....

 

So I thought, what the heck, I'll try re-installing a new t-stat and see what happens (maybe it was a bad t-stat?). Well, all the symptoms returned. (I replaced the rad. cap at the same time). BTW, t-stat is OEM.

 

So I remove it again, and overheating problem is gone...no more bubbling, no overheating, overflow tank at the correct level...

 

So my questions are:

-what am I risking, other than no heater on chilly mornings, and poor gas milage, by driving w/o thermostat?

-I *think* I understand how thermostat works, but I can't quite connect why removal of t-stat would have such dramatic difference...if I have a HG leak, it leaks weather t-stat is in place or not, right? Then it should heat up the coolant too rapidly, if slower than before? So I should expect to see overheated situation, right??? Or not?

 

Thanks for helping out a newbie.

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Without the T-stat you engine does not build up as much pressure and heat in the block. I know aftermarket companies offer different opening degrees but can you find one in OEM? Maybe yo could find one low enough that you could keep your T-stat and your heat/MPG...

 

Hope this helps.

 

I do believe the t-stat only operates on heat...not pressure. See what I am saying?

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Your headgasket problem, compression leaking into the coolant, causes overheating by producing tiny bubbles in the coolant. The pressure drop across the water pump has a tendency to expand these bubbles so that they collect and cause a gas pocket in the water pump. This stops the coolant circulation, and your engine overheats.

 

Without the t-stat, there is enough flow to keep the bubbles moving.

 

This is only a temporary fix, the HG leak will grow and you risk mixing oil and water and wearing out the engine very fast. Start saving for the HG repair!

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Burp your coolant system real good!!! If you have questions on how to do so please ask and I will walk you through it. Pretty simple. Alot of Roo's overheat because of air trapped in the system. Mine did it twice so but I burped it and had no more overheating problems.

 

 

Try some block seal as a temp fix. Maybe you could prolong the magic untill you can save up for the HG repair or a 2.2 engine swap.

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It's no big fancy procedure to burp your coolant system.

 

Just take the black plastic screw out of the passenger side of the radiator and fill the radiator until you see coolant coming out of that hole. Then put the screw back in and put the rad cap on.

 

Done it this way dozens of times...

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to answer your question, it won't really hurt your car to run w/o the thermostat....it'll take longer for your car to get warm, but in FL I don't think you likely have frigid temps so no biggee....

 

In my experience burping the cooling system can be a huge PITA. Go slow, be through, don't give up. Hopefully it's not the HG>

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I believe there is some merit to putting the car on a hill to do the cooling burping. I read about this on a Vanagon site once because they have problems like us soob owners with air in the system.

 

As for the person with the SUS....if you can get away without a t-stat...go for it and save your pennies. I did it once to get me by for a little while.

 

Matt

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to answer your question, it won't really hurt your car to run w/o the thermostat....it'll take longer for your car to get warm, but in FL I don't think you likely have frigid temps so no biggee....

 

I concur. When I lived in Maui my friend's Landcruiser had a overheating problem. His mechanic just pulled the t-stat out. Overheating problem solved. The mechanic said it wouldn't cause a problem since temps rarely go below 60.

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Most of the time these 2.5L DOHC head gaskets won't leak untill the engine is good and hot. Shops that are not familair with Subarus bad head gasket symtoms, have a hard time diagnoising the problem, because conventinal methods don't usaully work, and the engine needs to be hot to nail down the problem.

 

So it is very possible that with the T-stat out the engine never gets hot enough for the head gasket to leak.

 

Sooner or later is will probably degade to the point were this will no longer get you by. Plan on repairing it.

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and it won't make any difference. I have heard two theroies on why they overheat when you have the thermostat installed with a slightly shot head gasket. Number 1 is the one Setright has stated well and the other is that when the temperature reaches a degree that it can only reach with a thermostat in the gasket leaks.

This was demonstrated in a science class by putting a piece of aluminum on a bunson burner and watching it warp.

There is no question that the engine will maintain more temprerature with a thermostat in.

Who's right? I don't know and it would be very tough to test it.

I guess the lesson to take away is that the gasket leak can be minimized enough to run for a while with the thermostat out. This would not be very nice in Alaska, but here in CA he will get away with it for a while at the risk of furthur damage.

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Wow...what a great board! So much responses...thanks to you all!

 

 

It's kind of making sense to me now...the bay area is fairly mild weather-wise, but it still does dip into the 30's now and again where I live.

 

I thought I'd take a crack at this product:

 

www.rxauto.net

 

Run with it a while, replace the thermostat yet again, and see what happens...I'll keep you all posted.

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I beleive for the price of the 2.5's HG repair you could swap in a 2.2 with low miles. I have read a few threads on here regarding the matter so if you do a search you might yeild more results. I know alot of people either do the swap when they go or would like to.

 

Please don't quote me as I am only repeating what I have seen in other threads.

 

Hope this helps.

 

Maybe someone could post the link to CCR....

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  • 2 weeks later...
Wow...what a great board! So much responses...thanks to you all!

 

 

It's kind of making sense to me now...the bay area is fairly mild weather-wise, but it still does dip into the 30's now and again where I live.

 

I thought I'd take a crack at this product:

 

www.rxauto.net

 

Run with it a while, replace the thermostat yet again, and see what happens...I'll keep you all posted.

I've been driving the '92 legacy w/o thermostat for a year now without problems. In the winter time, I put a piece of cardboard in front of the radiator (about 80% the size of the rad). So temp is rising until normal operating temp (so I have heat). It takes a bit more time to have heat, especially at temp like this week with -10 farenheit. I remove the cardboard in summer time. I have a spare ej22 ('97 with 60k miles) for this car but there is no way to make it die, even with a HG problem...

 

Syd

Québec, Canada

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I thought I'd take a crack at this product:

 

www.rxauto.net

Here's a quote from their site that caught my eye: (emphasis added by me.)

 

"We guarantee that if you REPAIR THE PROBLEM THAT CAUSE THE HEAD GASKET TO FAIL IN THE FIRST PLACE and then faithfully follow the Thermagasket Application Instructions, you will repaire (sic) your vehicle's head gasket problem and have it back on the road for a fraction the cost of a conventional repair."

 

Say what? :eek:

 

Whole lotta double-talkin' goin on. My gut says steer clear.

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i've *heard*/*read*, though not from what i'd consider excellent resources as i really don't remember, that running without the thermostat can increase internal engine wear because the engine isn't maintaining as consistent of an operating temperature and is less frequently in the operating temperature for which the motor was designed or at which the engine was likely run for a fair number of miles previously.

 

that being said, you'll be fine. i've done it on more than one occassion and was just doing it up until i replaced my head gasket last week. after much abuse and not having the thermostat for a few thousand miles (and i've done this before as well) the 206,000 mile XT6 is running today as good as it ever has. and i was getting a rediculous amount of water in my oil as well, probably not good for bearings and such. the leak was slower with the thermostat removed (though it was still leaking way too much).

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  • 1 year later...

not to be a buzz kill, but i think a lot of you are missing some points about the thermostats.

 

modern engines are designed to run at a single, specific temp. the only time you should change the thermostat to a different set point is if you put on some aftermarket gizmos (chips, different turbos and boost,mostly) that remap the air/fuel ratios based on a new, custom thermostat setting.

 

running without a thermostat basically makes the engine always run at radiator capacity minus outdoor temp. only on a very very hot do would it actually get up to operating temp. on spring, fall and winter days, it will get at best up to a warm level, because the radiator is dumping heat as fast as it is produced. there is no thermostat to shut off coolant flow and maintain a constant internal engine temp.

 

in addition to moderately helping your headgasket problem, running without a thermostat is also: costing you gas mileage because the a/f ratio is wrong for the variable temps your engine is running; keeping your auto tranny from coming up to operating temp (it circulates through the bottom of the radiator); possibly fouling your catalytic converters with unburnt hydrocarbons; probably carbonizing your valves and injectors.

 

thermostats on a fuel injected engine are very important parts of the engine managment system and i wouldn't mess around without one too long.

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not to be a buzz kill, but i think a lot of you are missing some points about the thermostats.

 

modern engines are designed to run at a single, specific temp. the only time you should change the thermostat to a different set point is if you put on some aftermarket gizmos (chips, different turbos and boost,mostly) that remap the air/fuel ratios based on a new, custom thermostat setting.

 

running without a thermostat basically makes the engine always run at radiator capacity minus outdoor temp. only on a very very hot do would it actually get up to operating temp. on spring, fall and winter days, it will get at best up to a warm level, because the radiator is dumping heat as fast as it is produced. there is no thermostat to shut off coolant flow and maintain a constant internal engine temp.

 

in addition to moderately helping your headgasket problem, running without a thermostat is also: costing you gas mileage because the a/f ratio is wrong for the variable temps your engine is running; keeping your auto tranny from coming up to operating temp (it circulates through the bottom of the radiator); possibly fouling your catalytic converters with unburnt hydrocarbons; probably carbonizing your valves and injectors.

 

thermostats on a fuel injected engine are very important parts of the engine managment system and i wouldn't mess around without one too long.

 

agreed :)

 

nipper

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thermostats on a fuel injected engine are very important parts of the engine managment system and i wouldn't mess around without one too long.

 

 

Agreed. Running no t-stat on a car with a coolant temp sensor is essentially like driving a carburated car with the choke always partially on, as the CTS will cause mixture enrichment and it'll never run closed loop. If you really wanted to half rump roast it right, it would be possible wire up a switch and a resistor of the appropriate value in paralell with the coolant temp sensor to fake the computer into running in closed loop mode. Look at the chart of coolant temp sensor values for the normal engine operating temp (say, 470 ohms at 180 degrees.) Measure actual coolant temp sensor resistance at your typical running-no-thermostat-but it's as warmed up as it's going to get temp (say, 750 ohms.) Calculate the appropriate value of resistor to put in paralell with the 750 ohm CTS output to bring it to the appropriate value of 470 ohms. The formula for this would be (1/750) -(1/470) = 1/X With X representing the value of your unknown paralell resistance- in this case, 1258 ohms.

Once the car is as warmed up as it's going to get without the thermostat, flip the switch to make the ECU think the car is at operating temp and it will go into closed loop mode at least= better MPG and cleaner running.

 

Or, you could just do the job right & replace the headgaskets.

 

Nathan

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