Say Guys,<br>I was towing my 5er this past weekend and was bucking 30 mph headwinds and had to lock out of OD. I was watching my temps (stock temp guage) and they were huvering right around 200. I was wondering just where the danger zone is for these guages?<br><br>Thanks<br>Grampaw

 

Water boils at 212*

 

Pure water boils at 212 degrees F at sea level and standard atmosperic pressure. Water in a radiator does not. First it is mixed with antifreeze which raises its boiling point (also lowers its freezing point). Second, it is under pressure of approximately two atmospheres. I have no idea what the boiling point in the radiator is but is is well above 212 degrees.<br><br>Hovering around 200 is nothing to worry about, the thermostat is 190 degrees.

 

gosh been a long time but I think you get two degrees for every pound of pressure. IE 15 lb cap will get you 30 degrees over boiling therefore 212+30= 242.<br><br>http://www.watb.net/info/c_factor/pressure.shtml<br><br>http://www.biggreenegg.com/boilingPoint.htm

 

Grampaw, I think your question on a danger zone is dependent on the age and condition of the entire cooling system. I wouldn't worry about a 200F engine temp, but if it started rising too far I'd keep an eye on it and maybe lift the right foot. Any reading off-center (or off-normal) would warrant my attention. Remember, these guages are little more than idiot lights - something to give the avg user a warm and fuzzy, and not necessarily good raw temp values.

If you don't have one, a transmission fluid temp guage sensor in the hot line may be a good investment. A real guage. 200F there would have my attention.

 

Most of the big highway tractors have a 190F thermostat but have a 205F fanstat so most likely you would cycle through 210-215F before all cooling starts. You shouldn't worry until pulling on a long hill and the gauge maintains a high temp reading that can not be controlled or reduced. If it continously creeps toward the redline reduce speed and drop a gear maintaining maximum engine fan speed for air movement through radiator. Diesel engines produce more power the hotter the water temp and cooler the air intake within certain parameters. PK

 

Grampaw,<br> Probably wouldn't hurt to do a cooling system &quot;flush-out&quot;, refilling with new coolant and installing a new thermostat while you're at it, when you get the chance. Make sure that the radiator fins were clean along with the AC condenser, intercooler and transmission cooler. I don't think that I have ever seen my 99 run over 200, even while pulling the 10k 5er in the mountains during summer with the AC on. I have heard the fan kick on a few of those times though.