Bad Thermostat or Normal Ops?? Help please...

[rnbiker]

Okay... So I have a fairly modded C5 (2001 coupe) and among other things, it has the 160* thermostat mod.. Lately, it's been anywhere from 30 to 45 degrees outside and I was averaging about 158 to 160 degrees on the highway at about 70 mph. This seemed very cold to me and I wanted the car to be closer to at least the 180's - 190's with this kind of ambient temperature, mostly because the car seemed to "feel" like it was running cold (quirky a bit) and because I really feel that 160* is too cold to run these engines. Now, I'm not trying to get this to be yet another hashing out thread of what temperature is best, so I'll say that beforehand. My preference is for it to be a bit warmer. I've suspected that my 160* stat may have just been "stuck open" or otherwise faulty since my temps were so low, but since I couldn't find a readily available source for a replacment 160* here in OKC, I bought a stocker t-stat (187*). Now, with the same temps outside, it's cruising on the highway at about 210* and getting to around 225* putting around town. I should also mention, in case it is pertinent, that my engine has also been modded to the later LS2 water pump and therefore uses the seperate t-stat and housing and not my original LS1. My question is, should there have been THAT MUCH of a difference between the 160* and stock or was my 160* likely bad as I suspected? Also, should I try the 160* and see if it's warmer as I'd like it, or should I go in between and get the 170* that is available? Just seems that 158-160 was too cold and it NEVER got any hotter, but where it is now seems high. I did not change the fan points either and I don't know how much that matters (I know that it does, some), but should it matter that much?? Sorry for the long post, but any help is appreciated....

[Y2Kvert4me]

160 actual coolant temp IS too cold, but unless you have a higher capacity aftermarket radiator, most using a 160 stat don't ever see it actually run that cool.

With a 160 stat, mine runs 176-178 or so cruising.


The Tstat does nothing to control the upper end of the normal operating temp spectrum though, that is the job of the fans.
If the car has been tuned, the turn-on setpoints are usually lowered, this is primarily why lower temp Tstats are used, to allow for lowering the fan setpoints.

For example, mine is set that the low speed fan comes on @ 195, and turns off @ 185. This would be impossible with the stock Tstat, where normal cruise temps are right around 192 or so. If that combination was tried, the fans would likely run all the time because they'd be trying to cool to a temp below the Tstat rating.

Stock, the low speed fans on a 2001 will turn on at 224. Also keep in mind the fans will also run anytime the a/c or defroster is on, up to 35mph.


210 normal cruising is a bit high, unusual even for the stock Tstat. It's possible you got a bad stat, or also possible you sucked up a plastic bag or something else blocking the radiator airflow- always check that first because it only takes a few seconds to look.

Seeing 225 when idling or in traffic is normal, assuming fan setpoints haven't been altered. Without knowing what your fan setpoints are, I can't say if this is unusual or not for your car.


Many feel a 180 stat is the best compromise, especially if the car is used in colder climates. It still allows the fans to be programmed on sooner, but won't run too cold like you found yours was doing.

And you are correct, 180-190 is about ideal for coolant temp.

[rnbiker]

Well, that's the difference already between this place and CF.... I posted this same thing on there and while it took awhile for someone to respond on here, my first reply was usable information and not BS like I got on CF. Anyway, thanks so much for the info. I'm torn between the 180* and the 170* thermostats. I think that the 180* is cheaper ($20 vs. $89) and is more readily available (only know of one source for the 170*), so if it works well, that will be my choice. I would really like around 190 on the freeway if possible. I do know that 158-160* was too cold. Also, I have not had the fans adjusted by my tuner yet, but really was more concerned with highway cruising temps since as you pointed out, this is the temp more directly related to the temp of thermostat used and kinda takes the fans out of the equation. I'll let you guys know what happens. Cheers and thanks again....

[Y2Kvert4me]

Buy the $20 one.

And, while at CF, do an advanced search for subject "thermostat" with the username "vettenuts".
Thermostats are tunable to some degree, and I know he has an excellent thread there detailing how to accomplish this and how to test it's operation before actually installing it in the water pump.

Any help or replies you may receive from him over there is quality advice you can take to the bank.

I totally understand wading through the and hostility over there. There's still some really smart folks there too, it's just a matter of knowing who they are.

[Tulsa Vette Guy]

I prefer and run the 170 deg, My tuner suggested this to me.