'11 GS A6 with a DeWitts rad.

Regardless of ambient temps, I always run between 194F to 196F (mostly 194F) on the highway at anything above 45 mph or so. If I back off and coast for a distance, temps can drop down as low as 188. There was a 187F OEM thermostat installed.

The water pump and thermostat were changed last week for new OEM units. The shop swears that the thermostat was exactly the same as the one they replaced. On the way home, temps went up to 205F on the highway at cruising speed. Ambient temps were like around 60F on that day. When I got home and checked the coolant level, it was right up to the neck of the overflow bottle. I've never seen it that high. The shop does have a vacuum tool that is supposed to removed air from the cooling system, and they service many Corvettes there. It's not like it's their first rodeo. Either way, I called them up, and brought it back. Their first take on it that there must somehow still be an air bubble in the system, so they used the vacuum tool again to try to purge any air, but results were the same, except that the fluid level in the reservoir is more like normal after I got it back home, and it cooled off. Their take on it now is that the brand new thermostat is defective, so they've ordered another one. Seem like water pumps and thermostats are in short supply. I could probably get an aftermarket thermostat and bring it out to them, but then it starts making it my problem. That's why I want to stick with the shop supplying the parts. I know that this particular shop will make things right. Their work is guaranteed.

The car was running at the usual temperature (194F) when I brought it out to them, so the only thing that was changed was the pump, belts, and t-stat. I also checked visually for obstructions in front of the AC condenser, and between the condenser and rad. I all looks OK.

Any further insights to add? Could there still be an air pocket or anything else that I haven't thought off? It all kind of sucks, because we just started with some decent weather, but I really don't want to drive it on the highway for long if it's running that hot.

 

Don’t have an answer to your question but 205 isn’t hot, but well within the normal range. I’m anywhere between 195 & 225 if there is a lot a stop & go. Normal driving is around 205-215ish.

 

195 to 223 if in the city or stuck in traffic was what was happening before. But now I'm running min 205 on the highway, compared to 194 before. The problem with running 205 on the highway is the fan starts to ramp up at 199. There's no reason for the fan to be running at any speed if you are cruising along at highway speeds. That's what has me concerned.

 

I also have DeWitts and dual Spal fans. I run 205 - 212 around town. Stoplights no higher then 221 and soon as I get moving back down to 210 - 212. Highway around 200 and down hill 190. I also have OEM 187 thermostat. DeWitts said that is perfectly normal. Ambient temperature doesn’t make any difference.
My tuner has them coming on at 195 at 75 %.

 

My around town temps haven't really changed and they are similar to yours. It's the 11 degree increase in highway temps that I don't like and don't understand. I want it back to 194F. I've got the old thermostat and it was the 187F one. Either it's going back in or one close to 180 will take its place.

If you've got your fans set @ 75% for 195F, and your highway temps are 200 wouldn't that mean your fans are always running at least 75%? Just wondering.

 

You sure on the 187F OEM thermostat installed before, since the temp range you state, would be a 160* T-stat in play.

 

Pretty sure. It's marked 86C, so just under 187F. A pic is worth a 1000 words.



I thought the t-stat would be fully open around 7F above the rated temperature? Seems like that's the way it was operating before.

 

I did the coolant and T-stat replacement by myself recently, using an aftermarket T-stat from NAPA. After changing, the coolant temp go up 7 degree from 196F on highway driving. I find out the NAPA T-stat is for 190F. So I put back my old 187F T-Stat and the coolant Temp drop to 198F for highway driving. So I would suggest to wait for new T-stat and install it to see what gonna happen.

 

On factory thermostat on 2005 base Corvette I run 192 to typical 196. But it can go as high as 225 or typical 216. It depends how long idling in city stop and go traffic and weather.

 

Thanks for all the replies. Looks like there's some variation on what a stock t-stat will do, but I think the one they installed is out of spec. As suggested I'll see what happens with its replacement and be happy if I can get 198F (or less) on the highway.

 

Just to finish this saga, which turned into a goat rope, the original OEM T-stat is now back in, and it’s running steady once again at 194F on the highway. The OEM T-stat is rated at 187F (86C), so to me, this makes sense.

The shop replaced their supplied OEM water pump and OEM T-stat at their nickel, but that didn’t completely solve the problem. Now it ran between 201F and 203F on the highway. Not that it probably matters, but the second OEM T-stat was manufactured in Japan. This to me is still running too hot. Next, I ordered a 180F thermostat from Amazon – Stant 15158. Clearly advertised by Amazon as a 180, but when I got the box, the box was clearly marked as a 190F T-stat, and Stant’s web site confirmed that. Note to all – don’t necessarily believe Amazon. I filled out the return request, and the supplier’s response was to just keep it, and they refunded my payment in fall.

Next stop was RockAuto, where I ordered a MotoRad 523-180, a 180F thermostat which they listed as an alternate OEM T-stat for the Vette. When that arrived, I had it installed, but it immediately started leaking because as it turns out, whatever was in the box didn’t fit. I measured it, and it’s around 1/8” smaller in diameter. That was never going to work. So, back in with the very original T-stat. I guess it’s possible that there was a mistake at the MotoRad factory wherein the wrong T-Stat was put in the box, but I’m beyond caring at this point. I’m going to try to get a refund from RockAuto.

From all of this, I’m going to suggest that before you install any T-stat, at least compare the diameter of the one coming out to the one going in.
As a note, it's very difficult to properly 'burp' the system. I'm guessng there's a number of C6s driving around with air pockets in their cooling system and are running hotter as a result.

 

Would you suggest just stick with the factory part thermostat in this case from Chevrolet? No aftermarket parts to avoid all of these problems?

 

I put a Summit 160 and it works great. I run about 178 cruising and about 200-210 in stop and go with stock fan and Dewitts radiator.

 

I have a DeWitts radiator with an oem 187F thermostat and single fan. I run between 189F to 194F on the highway. In stop and go traffic it will run 205F plus. As soon as I get moving again it will quickly drop back down. If I keep the rpm's up (manual trans) it will run cooler because it is circulating the coolant faster. I also found that in stop and go traffic, if I turn on my AC it will drop the temp because my radiator fan will kick on and move the air through.

 

As for "burping" the system, I purchased a vacuum tool off of Amazon or eBay ( I don't remember which one) when I replaced my radiator this past winter and I must say it worked very well. I'll never replace coolant any other way again.

 

There were 3 factory thermostats in play - the 'original', and 2 others. Each resulted in a different operating temperature, but I've got no way to verify that the system was 'burped' properly on the latter 2, so maybe that's why they were running hotter. Of the aftermarket parts, 1 was mis-advertised and the MotoRad simply didn't fit. As I said, maybe they put the wrong item in the box, but I've no way to tell. There's no part number on that T-stat itself. I'm sure there are aftermarket parts that are just fine as members above point out. I'm putting the experience down to some bad luck and trying to point out where you can save yourself some grief by double-checking what you receive and making some measurements.

 

I also have a Dewitt's radiator on my cammed Z06. I run about 193-195F when moving and just over 200F stop and go. I have a Lingenfelter 180 degree thermostat installed.

As far as burping the system. I have found this to be the best and most cost effective way to do it. Take a look at this pic. The attached funnel is filled with coolant. All you do is start the car and let it heat up till thermostat kicks on and it will bubble like crazy so make sure the lid is on the funnel. I have used this on Honda, Subaru and now my Corvette with perfect results!

 

I wish I had seen this before I did a coolant flush today. I was having issues with getting the system to burp and I knew there was air somewhere. I wound up taking the vent tube off and hooking a vacuum pump to it. Took about 20 or 25 pumps for it to pull fluid to the end of the vent tube. Think all is well and an alternate solution.

 

stock Tstat 195 degrees

 

Incorrect. LS3 OEM thermostat is 187 degrees F or 86 C.