What is the purpose of a thermostat?

[renaissance man]

Weird question I know but, bare with me...

My cobra has a 180 degree thermostat. I am running at about 190 degrees on the highway, 210 degrees at a standstill.

Question is: Wouldn't it behove me to remove the thermostat to allow the coolant to be more effecient at a lower temperature? God only knows, we don't care about cold weather here in Austin, Texas. The car heats up in two minutes flat! Just thinking that the temperature would run at perhaps 160 degrees without the thermostat? Or is it that the temperature is what ever the operating temperature of the engine is?????
Wheew!!!!

[SilverCobra]

Ren Man - the information manual that came with my Southern Automotive engine suggests not to use a thermostat. What is actually says is to take new or used thermostat and punch out the mechanism so that there is a hole about the size of a quarter in the thermostat. This will provide sufficient water restriction flow to provide the proper cooling temp. It goes on to say that if you absolutely feel you must have a thermostat - run a 160 degree thermostat. I guess you could go to a 160 thermostat and see what temps you run. If still not satisfied, punch out the center and try that. You might call Louis at Southern if you want it from the horse's mouth. I'm sure they would give 2 minutes of free advice even if you are not a customer.

[Satanpez]

I've read a bunch of things on this, who knows what's right.

At 160 degrees supposedly the oil will eventually turn to sludge. Oil is supposed to operate at a higher temperature.

At that temperature emissions will be higher. (Not that anyone here cares)

Without a restriction/thermostat your engine will take a long time to warm up, then it may overheat because the water flows too fast through the radiator for it to cool off.

-steve in nj-

[renaissance man]

Thanks again Dick,

Would you agree that my running at 190 degrees on the highway and 210 at a stop is a bit much? Perhaps the 160 thermostat would be a bit better?

[Lyle]

Renaisance Man,

There are several views on this issue:

1. Some say that running without a thermostat does not necessarily make a car run cooler. For regular cruising, the engine probably will run cooler, but the cooling system was designed such that the water needs to stay in the radiator for awhile to have a chance to cool down. Even when wide open, a thermostat is somewhat restrictive and slows the flow of water through the radiator. Supposedly, at some level of thermal load, removing the thermostat can make the car run hotter. (I've never worked an engine hard and long enough to verify that.)

2. Engines, especially ones with EFI, are supposedly more efficient at "normal" operating temperatures. Some of that has to do with clearances being set for "normal" temperatures, and some optimum combustion chamber temperature. Some of it also has to do with emissions - hotter charges burn more fully, so fewer emissions. (Luckily for cobras in Arizona, we don't have to worry about that.) In any event, performance is most consistent when water temperature is constant.

3. The correlation of temperature and power has many parts. A cooler engine has a cooler intake track so should ingest a cooler charge. A cooler charge is denser, has more oxygen, so more power. Another change by lowering temperature on an EFI engine is that the computer responds to lower water temperatures with a somewhat richer mixture. It may have to be alot cooler to make much difference, but if the engine is cool enough that the computer thinks it is in the warm-up phase, the computer will fatten the mixture noticably. Did you ever notice that your EFI car seems strongest during the first two minutes of running?

So, you can take out the thermostat, and it will probably lower your operating temperature under normal operating conditions, but you may end up with other problems. I've tried it on different engines over the years, and always ended up putting the thermostat back in.

Your temperatures do not sound all that bad. If your 180 degree thermostat gives you 190 degrees on cruise, your gauge may be off. You can confirm that the thermostat is calibrated right by putting it in a pan of water with a cooking thermometer, and heat it up until it opens. It should crack open at 180.

If you want to improve things, you might do better by working on airflow over the radiator, or making sure that your water pump is giving you adequate flow.

For what it's worth.

Lyle

[renaissance man]

Awesome Lyle,

Thanks for the input. All points seem sound. I even have my fan hard wired to a manual switch which I throw to keep the engine cool. It just seemed a bit hot to me?

Steve,
If you are running Mobil 1 or other purely synthetic oils there will be no sludge. They flow better and won't breakdown even at twice the temperatures.

Anyone else care to chime in???

[dalola]

Gentlemen,
Keep in mind, a thermostat's purpose is to maintain a MINIMUM coolant temperature. If you have a heat problem, a colder thermostat will not resolve it.

For oil to properly due it's job, it must maintain enough heat to keep some impurities burnt off, and provide optimum protection from metal to metal friction. Granted, if a short engine life is acceptable, colder temps can be run. I would avoid any temp less than 180F for coolant, and a minimum of 200F for oil. Heat is not always the enemy it's made out to be, unless excessive, of course. Excessive cold temps can be far more damaging, especially in the long term.

Regards,
Dave

[renaissance man]

Dave,

So, you think my 190-210 degree range is fine?

[Lubrecon]

Ren,

Remember what you are seeing is the coolant temp, not the oil temp. In most cases, the oil temp will run about 210-220 F. It sounds like you have a flow problem, either water or air. At hwy speed, you are getting a ram air effect, and even though the temp is 190, it does not look too bad, maybe 5-7 degres high. But as soon as you lose the ram air effect, the temp comes up. 210 is too high. The coolant temp you see on your gauge should be fairly close to the thermo's opening point, and it should stay there unless there is an excessive amount of idling or the ambient temp is high, I know, I live in Houston.

Removing the thermo may lower both the hwy and slow driving temps, but you are really just masking the real problem. It will cause the temp to rise slower, but may not let the engine reach a good operating temp. The oil needs to be hot to drive off lighter ends like fuel dilution.

Also, check your timing. If it is too advanced the engine will run hot since it fires early and the charge gets compressed further after ignition, increasing the cylinder temp. Also a lean fuel condition will cause an engine to overheat. The gas actually contributes to combustion chamber temps, maintaining proper cylinder temps with some cooling. Too much air in the charge and you lose the cooling factor.

Sorry to ramble, but air and water flow really sound like the problem based on when you see the temp rise and lower.

One other thing. Check the coolant concentration. Too much antifreeze can be part of the problem also. But don't run just water, you need some corrosion inhibition.

Jerry

[renaissance man]

Jerry,

You are correct about the Ram Air. the air filter is right in the hood scoop unless I'm not understanding your point?

What is your best guess to remedy this "flow" problem?

Thanks

[Cobra20646]

Dave,
You mentioned your cooling fan....
How is it wired to the 12 volt source?
The reason I ask is how I found mine wired. It was not thermo controlled, but ran all the time the ignition was on. The wiring was too small for the current demands, and the switch warmed up too (heat = voltage loss). I wound up with just under 10 volts getting to the fan motor, with the engine running. Rewired the fan using a 30 Amp control relay, 12 gauge wire to the fan relay (relay only 6 inches from fan) and now I loose just about .3 volts, fan runs FASTER and I immediately noticed an improvement in cooling when the car was sitting at idle. Used to go over 200 to about 210, now runs just a tad over 190.
FWIW.. my 2 cents today
- Jim -

[renaissance man]

Jim,

My fan is as your's was. Manual to a switch on the dash. I can turn it on at will. Usually kick it on right after starting the car.

[Cobra20646]

Dave,
Get an accurate volt meter and measure the voltage at the fan, and at the back of the alternator. The difference should not be more than half a volt. If it's more, your loosing fan speed that equates to a loss in cooling efficiency.
- Jim -

[renaissance man]

Thank Jim. I'll give the details tomorrow.

[Lubrecon]

Ren:

Your question has nothing to do with the intake air scoop. We are talking air flow through the radiator and water flow through the water pump. The answers about the fan voltage are good, so check that out. As far as flow is concerned:

Water: Be sure that the belt is tight so there is no slippage and the water pump is turning the right speed. Check to see that you have the right size pully on the water pump, it can make a difference. Is rotation right? If the impeller vanes are old, they might be worn or corroded and not put out the right volume of water as when new. Be sure the radiator is not restricted in any way so the water can flow through as designed.

Air: Be sure there are no restrictions to the air flow through the radiator, there shouldn't be but look. The Unique's have pusher fans, and some have pusher and puller fans, give that a thought.

Cooling demands increase with load, and at idle with no load, the cooling demand should be lower and the temp cool down. With yours heating up at low speed, it would be logical to look at the flow, water and air, as I have suggested.

Call me it you like, 281-890-6400

Jerry Shelby

[renaissance man]

Thanks for the clarification Jerry. I have a 16" puller on the radiator. I think its about 1900 cfm??? As for the pully, I'm running a single pulley on a "March Underdrive" pulley. Water pump is brand new but perhaps I need a more agressive pump???
How do I know if the pump is moving at the right speed??? As for, "Is rotation right", do you mean in the right direction?
Perhaps I should let my fan "off" since it's wired to a manual switch and let the air through the front intake do the job unless the temp hits 180 or I'm in the city or at a standstill?

Sorry for the stupid questions, but I'm learning every day!

[Lubrecon]

Pully diameter determines the rotational speed of the water pump impeller, smaller pully, faster rotational speed, bigger(diameter)slower speed. Unless the belt is somehow reversed around the pully, it has to be rotating in the right direction, forget that idea, it would have to be really messed up.

Make sure the pully diameter is right.

1900 CFM sounds good. But is the voltage right to get that volume. Check out what the other guys said about voltage at the fan.

Jerry

[poorboy]

Ren;
The temps you are running are not excessive. A lot of the newer cars have thermo switches that have to get up to 240-250 to even work. The thermostat is to warm up the engine quickly as well as maintain a constant temp. Taking out the thermostat is an old shadetree patch. Fans running at hiway speeds can reduce air flow though the radiator. I run mine only when slow or stoped. Also with under drive pullies at idle your pump may be turning to slow.

Poorboy

[K.Wilson]

Ren Man,
Check to see if you have a "reverse rotation" water pump. A 5.0 (302) pump as used with a serpentine belt will fit on a 289 but would turn the wrong direction with a V belt system. If this is the case you would still have water flow but at a much reduced rate, and would cause overheating.
I went through an overheating problem with my big block only to find the pump impeller was loose and slipping on the shaft. It took two weeks of detective work to locate it.
Keith

[427sharpe]

210 is within normal operating temperature! Remember, a thermostat is rated by the temp at which it is fully open--in this case 180 degrees. Normal operating temp ranges from 165-220. A lot of the newer fuel injected cars have fan relays set near 200! You're fine if you stay at 210 at hot idle, parked. Forget it, and enjoy the car! DO NOT RUN WITHOUT A THERMOSTAT IN A STREET CAR!