How hot is too hot?
 

Im trying to get some better gas mileage out of my wife's 2001 Altima. She's getting about 22mpg with mix driving. I put in a 195f thermostat and just recently purchased a scangauge. Im noticing the radiator fans are coming on much more than before and according to the scangauge I have a water temp of 220f. I pulled the thermostat and tested in a pot of hot water and it does open completely at 195f. Is 220f too hot?

Hm, I would like to know this as well, as sometimes I go 208 of so

I would say 220 is too high. Ethylene Glycol starts to break down at about 229 degrees. If you scan gauge reads 220 its likely parts of the engine the coolant contacts are greater than this.

That sounds very boderline IMHO...Did you ever test the Water Temps with the OEM Thermostat? Usually you are aiming for about 100C or 212F...not too much over in general.

Seem when talking to Miro at Synlube he did not recommend running the Toyota engine any hotter as it would make the A/F mixture rich to provide additional cooling and you have the cooling fans turning on as well. Fans in my xB turn on at about 209F and normal temperature is 182-184F running it with grill blocks I get 186-190F which allows me to get more hot air out of the heater and it cools off more slowly when parked.

yes, 220 with a 195 thermostat is bad. BTW, what are you using to red the temperature? factory gauges are notoriously inaccurate. not 30 degrees innacurate though.

ANY time the engine is running hotter than the thermostat rating, either there isn't enough airflow over the radiator or the engine is being unreasonably loaded.

Hello -

(all temperatures are in degrees F)

On my scangauge, my original T-Stat ran around 180. My new T-Stat runs around 190. The Saturn ECU/PCM will turn on the electric fan if I hit 220. It doesn't stay on long, however. I think it turns off at 210. I don't like that because it cycles on and off too much in a higher temperature range.

To make sure that I have 100% control over my coolant temperature, I installed a manual electric fan override switch (thanks www.saturnfans.com !!!). When I hit 210 degrees, I turn it on. When it drops back down to 190, I turn it off. That way, I don't approach the ECU/PCM "danger zone". Also, the 20 degree swing from 190 to 210 takes longer to reach, so I don't have to toggle the switch as much.

I do have a temperature on/off monitor gizmo, but I am too lazy to install it and I am also saving it for something else.

I have heard that 250 is the absolute danger zone, but I will trust that 220 is the highest I ever want to go. At this time I wouldn't fear running at 200. However, I haven't researched a T-Stat for that temperature.

I use the Prestone coolant (green stuff) in my mild SoCal climate. I don't use the orange stuff because my mechanic said it gunks up the radiator.

CarloSW2

ahh yes the ornage stuff vs green stuff. as long as you dont mix the 2 they perform equally well! they dont "gunk up the radiator" unless you combine them (makes a jellowy substance)

my truck doesnt get awaywhere near 210 stays around 170-180. doesnt use a drop of coolant or oil and stock everythign at 140K miles... 210 is pushing things.

Higher temp=thinner engine oil ???
 

Is that true that higher engine temperature makes thinner engine oil? If yes is it good or bad thing.

The fans should not be cycling that much. They shouldn't run at all on the highway, especially this time of year. It may be your water pump is going out. Or you have a dirty radiator. You might try the old thermostat and see if it still hast the same problem. I drove a 195 tstat in a 98 altima with NO noticeable difference. In 40f weather I could also block 60% of the radiator and still easily maintain temps under 200f.