How hot is too hot?-Engine temp

[Larry Fisk]

I have the 525 CAT engine in my Thunder and I had Petterson CAT in Oregon replace my coolent with the extended life coolent. The tech that performed the job said he replaced my thermostat with a 195 degree one instead of the factory 185. He never said why this was done but now my engine runs at 195 on level road and can get as high as 210 degrees on a big hill. Does anyone know how hot is too hot and why the thermostat was replaced with a higher temp one?

[Edward Buker]

Larry,

That is worth researching and getting to an explanation that makes sense. I would think that you would want to run cooler if you had a choice, it gives you a little more thermal reserve before reaching any high derating limit. It may also be a little easier on other components in the compartment like alternators. I have seen as high as 205 degrees under extreme conditions and do not know where the upper limit is set.

Later Ed

[Gerald Farris]

Larry,
There are several reasons for the higher temperature thermostat. Mostly the higher temperature thermostats are used for a more complete combustion for emission controls. The more complete combustion may also increase fuel mileage, but not enough to notice. He probably installed the 195 degree thermostat because the 185 degree ones were out of stock at the time.

I think that the derate temperature is about 230 degrees. So you are not in danger of hitting that, and the engine should operate properly at 195 degrees, but I would prefer the lower temperature afforded by the 185 degree thermostat. I do not know how your shop feels, but I would not have changed your thermostat to a 195 degree unit without consulting you first.

Gerald    

[Steve Huber]

Larry,
On my C12, the Check Engine light comes on at 217 but derate doesn't occur until the temp Gerald noted.
Steve

[Larry Fisk]

Thanks for the replies, I have never had an overheating issue even on big grades. I think I will look into the 185 thermostat change over the next time I take it in for service. I would prefer to have the engine run cooler unless Peterson CAT has a real reason for the 195 thermo's. Hopefully changing these is not a big job and lots of money. Thanks again for the replies!!

[Joel Weiss]

I've spent some time reading trucker forums on this topic and it appears that the 195 degree thermostat is quite normal for this engine.  From what I've read the fan should be programmed to come on at 207 (for a C12). The thermostat is set up to begin to open at 190 and will be fully open at 206. This would agree with what I've seen with my new thermostat; it is very much "controlling" engine temp in the 190-195 range.  I wouldn't be at all surprised to learn that mine was also changed from a 185 degree to 195 degree one.  Since CAT says these engines should only operate at temps above 180 all these numbers seem to tie together.

Despite the low usage our engines get, don't overlook the fact that this is a scheduled 3 year replacement item; I decided that 13 years was enough beyond the scheduled change interval to justify replacement. The pictures I've seen online of used thermostats don't look very pretty with respect to crud buildup. It's not an expensive job whether or not you do it yourself. The part is in the $50 range and the thermostat housing was very accessible on top foe the block (much to the relief of the tech who did the job).

[Larry Fisk]

Thanks Joel! That's some good information.

[Bill Greene]

Informative forum. On a recent trip (Jul) to TX, our C12 ran its normal 188-190 but this pass Friday it ran 194-195 and on one occasion hit 197.  We came into some rain and the temp dropped to 185 but creeped back to 195 after leaving the rain.  I suspected something changed about the radiator, perhaps a plastic bag but have not found anything yet other than a dirt dobber nest, not large enough to raise the temperature 5 degrees i think.  But I don't recall that the thermostat has been changed in the 9 years we've had the coach.  From this forum, it is overdue but I'm less concerned about the 5 degree rise now after reading Joel's comments.  Very much appreciate the sharing of experiences these forums offer.

[Gary Winzenburger]

I've never owned a diesel motor before, so I'm still learning. The word "derate" is new to me. What does it mean in terms of upper temperature limits? All I know, and observed is that my CAT 3126 purred at a fairly constant 188 degrees this summer on some pretty hot days (95+).
Thanks for all the good information,
Gary

[Gerald Farris]

Gary,
The term derate is used to describe what happens when the engine computer (ECM) receives data that indicates continued operation at full power will cause potential damage. So the ECM restricts (derates) the power output of the engine to prevent damage. This will give the driver time to get off the road and shut the engine down. However if you continue to operate the engine and the problem gets worse, the ECM may prevent operation completely.

Gerald  

[Gary Winzenburger]

Thanks Gerald!