Tommy 35 SS

Currently I have a 160 degree thermostat for the Camaro in my sig. I've been getting crappy gas mileage for a while now and especially since after I've re-geared obviously, around 16 mpg with 50/50 highway city. And by highway I've actually mostly driving 55 mph.

I've heard lower degree thermostats can have an effect on gas mileage. Since I'm running an auto with the cooler lines still running through the radiator (I do have an auxiliary cooler also) I thought I'd switch up to a 180 degree instead of back to stock along with having a little more protection from pinging/detonating

I heard the right temperature range for stock internal LS1's is 190-210 range, right now I'm running 170-180 (according to a scan gauge I have) for the 160 degree thermostat so I'd imagine a 180 would put me 190-200 range. According to Carnot's theorm I believe, a engine that runs hotter should have better thermal efficiency or something like that IIRC

I do know because of the scan gauge it's getting warm enough to get out of open loop mode which causes really bad gas mileage I hear, so the 160 is not causing that like some people claim

Please no comments like "it's a V8 what do you expect", I've read gas mileage threads and people are getting much better than me with things like stalls and built engines

So should I go 180 or stay 160? Or go back stock which is something like 186 right? Would it be worth it? My low speed fans come on at 175 or 177 I think, I imagine I would need to change that for a 180 to keep from burning up the fans?

Thanks y'all

RPM WS6

iTrader: (3)

I'm not a fan of 160° t-stats for non-power adder, stock compression LS1s. LS1s run great in the 190-210°F range, and I've never seen any increase in performance from running temps lower than 190°.

The stock t-stat is 86°C/187°F, and with the proper fan settings will allow the engine to stay in the 192°-205°F range most of the time, but you may see higher temps since you live in a hot climate.

You might notice a bit of MPG improvement with the higher temp t-stat, but it's not going to be drastic since you've already confirmed that the PCM is operating in closed loop as it is. Your 3.73s will hurt highway mileage more than someone with a big stall who is still using stock gears. There may be several issues combined that are dragging your MPG down (tune, gears, t-stat, aged O2 sensors, aged plugs/wires, dirty MAF, vacuum leak, low tire pressure, etc.). Even if none of these are causing a significant problem alone, little inefficiencies can add up to a loss of several MPG.

Tommy 35 SS

I hear ya on the gears, the only reason I went 3.73 is because I want to do a 6 speed swap down the road and thought I'd have some fun with the auto in the mean time. The plugs/wires, tire pressure, and MAF are accounted for. The tune is from G-force motorsports, I'm not good with the technicals on tuning but I have asked them if it would affect gas mileage in day to day driving and they said no. I can't account for the 02 sensors, and I should say that my gas mileage was poor at best before I changed the gearing like 17 mpg with highway driving, if I 'hypermiled' the damn thing it would do 20 mpg, but talk about a pain in the ***. If I 'hypermile' now it'll do 19. When I say hypermile I mean like getting the most out of every last drop of gas out of the thing Like by driving 50 on the freeway, coasting a 1/4 mile before stops, and being out accelerated by school buses

So you do think it'd make a little difference to change the t-stat? I heard throttle response, drivability, etc. goes back up when changing the t-stat back up to a higher temp? (I changed other things at the same time so I don't know what the effect was of going from one t-stat to the next, probably not the best idea)

Tommy 35 SS

Also no vacuum leaks that I know of, I recently fixed one about 8 months ago

RPM WS6

iTrader: (3)

It certainly can't hurt, but I wouldn't expect to pick up several MPG based on that alone (considering you have confirmed closed loop status even with the current t-stat). It's correct that an engine will perform best with a nice warm combustion chamber, but a cold air intake charge. People will reduce coolant temps in an effort to keep detonation away in high compression and forced induction applications, but usually the only reason to do this for a stock engine is to keep the intake from heat soaking. LS1/6 intakes are not prone to heat soaking to the degree of a metal intake, so you don't gain much by reducing coolant temps on a stock internal, non-power adder LS1.

Again, my experience is based on my climate, which does sometimes get pretty hot in the summer, but not as hot as Texas. In my personal experience, the "sweet spot" of balance between best engine performance and MPG will be somewhere in the 190-210°F range, and this range can be attained with a stock t-stat and modified fan settings.

Having said that, another factor that effects MPG is fuel blend. Some lucky members of this site still live in areas that provide non-ethanol gasoline. These people will always see better MPG than those of us that are forced to use E10 (10% ethanol). So keep that in mind when comparing your mileage to others. Furthermore, as the outside air temps drop this time of year, the air becomes more dense and more fuel will be required to maintain optimal mix (not to mention the longer warm-up period of the engine due to colder outside temps). Some regions also switch to a different blend of fuel for the winter months, this winter blend usually further reduces MPG (not sure if TX does this or not).

You could replace your O2 sensors if they have a lot of mileage on them, but even still you might not see a huge boost in MPG. I don't think I've ever gotten better than 24-25mpg on the highway with a stock A4 car, and more like 18-19 with a 50/50 mix. Doing any city driving at all seems to really knock the MPG down.

Z28Z06

iTrader: (2)

My 2000 A4 with 3.23 gears gets about 21 mpg driving on the highway, used to get 22mpg but I think a vacuum leak is might be knocking things down a bit. I put in a 180 or 190 stat and turned the fans on at a lower temp, but didn't notice any real differece in performance or mileage. In a warm climate your engine will run above 160 degrees, but in cold climates you might be washing the cylinders with fuel as the computer will keep the engine rich. The LS termostat housing has a o-ring gasket and you can change it with out any real hard work, and you can put in new coolant as a bonus. Try a warmer one just to see if it makes a difference.

Tommy 35 SS

Ok that makes me feel better to hear numbers like that. The stock revised rating is 23 on the highway and that's what I used to get stock. We do have the stupid E10 stuff down here also, messes up our boats too.

I have 58,XXX miles on the car, so I think I'll hold off on the 02 sensors until at least 75,000. The numbers I was hearing in a different thread were way up there and I remember reading about a guy who had heads, cam, stall, 3.73 gears and was somehow getting 25 mpg at 90. There were a lot of other posts pretty high too. I guess you can't believe everything on the internet

Tommy 35 SS

I think I'll do that, and that's what I got too was 21-23 mpg when I was stock. it's good to hear realistic numbers.

Should I go with a stock one or 180 degree? If I find a used stock one would it be worth trying? I forgot that the thermostats were 50 bucks, or at least they were when I looked up the price, shouldn't have gotten rid of my stock one

RPM WS6

iTrader: (3)

I would agree. At that low mileage, unless you're getting a code for a bad O2 sensor, I wouldn't bother replacing them either. My '02 car has 101k miles on the stock O2 sensors, and I just managed 23.5mpg on a recent trip with 75% highway/25% city driving, on the winter blend version of E10. This is an air lid/catback only A4 car with 2.73s, just for reference. My average speed on the highway was 65-70mph. Again, when my driving is more of a 50/50 mix, the MPG usually drops to about 18-19, and 100% city is only about 2mpg lower than that.

Tommy 35 SS

Ok thanks. I think what I'm going to do is get the 180 degree when I feel like spending the money and install it and report back here what difference in mileage it makes, if it does. I'll do a loop of some kind since I can measure my mileage with the calibrated scan gauge and try to keep variables to a minimum.

Will I need to go back to my tuner to change the fan temperature settings or should anybody with the right equipment be able to change it?

What temperature should they be at?

Would I need to go back to have my car re tuned because I changed the coolant temperature?

Thanks again

printmanjackson

iTrader: (1)

I've been running the 160* thermostat for a couple years now and I'm going to change it not for better mileage but to get the engine to a better performance temp plus get the oil temp up. I have been watching this for a while and in my climit here in west Tn. we get big temp swings. In the summer the water temp will run 185-195* and the oil will get to 195-200*. In this colder weather we are getting now the water runs only 178 but at idle can get to 190. But as soon as I start driving it drops back down. Oil temp never get over 190* and it take a while to get warm.

I ordered a new 180* therostat and put it along with my stock 190* in a pot of hot water with a thermometer and watched for the opening point and closing points.

The 180* thermostat starts to open at 190*, fully open @ 195* and closes at 180*.

The OEM thermostat starts to open at 195*, fully open @ 200* and closes at 190* (maybe 187*)

So what I'm thinking is running the 180* thermostat and setting the fans to 195* on and 185* off. This should hold the water temp @190* and allow my oil temp to get to >195*. In the summer I'm thinking that the second fan setting can be used to hold this same temp.

Thoughts?

RPM WS6

iTrader: (3)

Anyone with LS1 tuning software should be able to adjust the fan settings. But you'll probably get the best deal on this by going back to your original tuner (sometimes they'll make minor changes like this for free or very cheap if you've already paid for a full dyno tune).

With a stock or 180 t-stat in the heat of summer, the coolant temps will usually stay in the 190-195 range even if you never shut the fan off. So keeping that in mind, I would have them cut off at no lower than 195.

Only reason why this could be an issue is if your tuner set the timing up on the ragged edge of detonation, at which point a higher coolant temp (and thus hotter combustion chamber) might require some timing adjustments. So the answer to you question depends on how aggressive the tune was.

My thoughts are that once the engine has warmed up, you'll never get it cooled down to 185°F with a 180 t-stat on hot summer days. I've used both a 180 and the stock 187 units, and even the 180 t-stat never allowed the coolant temps to drop below 190-192°F once the engine was fully warmed.

I think you'll need higher fan settings. More like on @205, off @195.