why would you want that thermostat? Isn't it better to run the engine at specified temp?

 

I would be interested to hear why people run a different thermostat as well. I fail to see how it would provide any power gains nor any fuel efficiency improvement. Perhaps if you have a fuel computer and you lean out the air/fuel you might want to run a cooler thermostat but on a stock engine I would be surprised if there is any benefit at all.

My $.02

 

If you do any extended amount of racing(for example me ) then you will want the coolant temperature to be lower. Basically the system has a bigger heat absorbtion capacity.

I'll try to explain. The factory thermostat is set at around 185F. Water boils at 212F(100C). The coolant system has antifreeze mixed in so it's not pure water, and also the system is pressurized. The coolant raises the boiling point higher. And if you are still brushed up on your chemistry, you will know that a higher atmospheric pressure will raise the boiling point as well. This is the reason why people install 1.3bar upgraded radiator caps. It's to maintain allow higher temperature before boiling over. Now that's the scientific part.

To make it simple. Boiling over = very bad. So you want to do whatever you can to prevent the coolant from boiling over. Antifreeze mixed in the system is the first step, more pressure is another advantage. With those 2 you're at say around 250F till the car will boil over. Too much coolant in the system is bad as well because coolant doesn't transfer heat as well as pure water. In some race cars the coolant is maybe only 15-30% vs a street car that is usually mixed to around 50/50.

Now back to the original question. Why get a low temp 160F thermostat? The big reason is so the coolant has to rise an extra 20F to reach that boil over point. So going from 180F to 250F is a 70F degree margin in the cooling system capacity. You technically increase the coolant system capacity if it has to go from 160F to 250F and it has to work 90F to get there. This gives you that much more margin when racing to prevent boilover.

If you remember from your high school chemistry/physics. When a liquid changes state from liquid to gas it expands at a much greater rate. When the cooling system is overwhelmed and boils over. It basically creates so much pressure because of the liquid to gas that the radiator hoses pop off. It usually ends up in a big steamy mess all over the engine bay and will leave you on the side of the road or race track.

All this is just a stopgap for an overwhelmed cooling system. Optimally you don't want the coolant temperature to stray too far from the starting point(thermostat rated temp). A bigger radiator will help keep the temperature in check if more heat is being produced by the engine. But if there is so much heat, even the big radiator will get overwhelmed after a while. The lower temperature thermostat and higher pressure radiator cap will allow you a bigger safety margin before the system boils over.

Obviously by now you can understand that a lower temperature thermostat is only truly useful in a high performance car or in one that will be raced hard on a track/road course. It might sound all well and dandy, but there is a downside to the low temp thermostat as well. As you all know the engine is basically a big thermal energy/air pump. It operates more efficiently at higher temperatures. These engines are designed to operate most efficiently at 180-200F. If you start lowering that temperature too much, you will lose some power and gas mileage.

Hope this helps clear some things up for those of you who have wondered what is the purpose of all these cooling system upgrades.
Sorry if it's too technical, but most of this stuff is only really useful if you seriously push the car to the limits

 

Jeff, this was a long and very informative post. To be honest, I pretty much knew most of it, and it just reaffirms my understanding that for regular driving the low temp thermostat will only hurt fuel economy and performance.

 

I ordered an OEM thermostat for my '98 SC400, what I recieved has a flange dia. of 2.2" (54mm) my original stat is 2.5" (64mm), every stat I have checked on for this car states a 2.2" dia. I refuse to go to my local (Tampa Bay) dealers because they are A** holes and charge double the MSRP for any part I have called about, also treat anyone that doesn't have a new Lexus like dirt.
Can any one on here clear this up?...Please? Where can I get the correct thermostat for a 1998 SC400? Thanks.

 

Try one of our vendors,Carson Toyota.don't know what shipping would be.

http://www.trademotion.com/partlocat...layCatalogid=0

 

Hey Jeff...very informative, its nice to read posts like this. Whats your thoughts on the thermostat a person can purchase from autozone or napa...they offer a 170 for our cars? Just wanted your thoughts...

 

item is discontinued. they still have some in stock.

 

way to revive a thread from ALMOST a year ago for that info....lol

 

sorry for resurecting an old tread, but how to install a new thermostat?
Do I need to drain all the fluid first?
A quick answer will be greatly appreciated because I plan on changing mine in the morning. My temp gauge is going nuts. When I'm at a complete stop the needle starts to rise then when I take off it goes back to normal. Coolant is topped off, and the radiator was cleaned. I also will be replacing my cap as well.

Thanks in advance.

 

No, you do not need to drain all the coolant, about 1/4-1/2 gallon from the radiator. However, your problem does not sound like a thermostat issue. Do your fans come on at all? At about 220 degrees the fans should kick on. If they do not then the temp switch and/or fans could be bad (also associated relays and fuses should be checked).
Doubtful but you could have a severly worn water pump -- when sitting at a stop put the car in neutral and brings the revs up to 2K or so -- does the temp drop? If so then the water pump should be replaced.