Seems like the universal "first mod" is a lower temp tstat and fan controller... makes sense.

I guess I'm missing something. 192 degree tstat, coolant running through the throttle body heating the intake air, std fan on/off settings in the 220 degree range... why did GM design the C5 to run so hot?

 

Hmmm..... I'll take a wild guess. :crazy:

GM produces cars for the general public and although most of us on the Forum are performance minded - there are some who buy vettes just as "transportation" to look :cool:

So, I'm guessing the General put the 192 stat in for 'quick' easy starts so you won't hafta wait ~ even in cold winter temp. ......Plus they are based in Detroit ! :lol:

Anyways..... for us Southern boys & gals.... a 160-stat makes better sense. :yesnod:

 

Sorry, Verskel, tstat doesnt even 'exist' when the car is first started. The Tstat will not make a motor warmer/colder than any other from a fresh cold start. Ambient temp rules here. Anyway, it is known that certain cylinder temps promote best combustion characteristics with regards to smog. secondarily, too cold combustion temps (all influenced by engine coolant temp) will not support thorough combustion of AF mixture, thus, leaving behind carbon deposits that can amount significantly. This leads to increase CR, hot spots, etc. Not good.
Lastly, I have experimented with various coolant temps at the drag strip: on the same day with all else being relatively equal, 195-200F coolant temps produce the most power (trap speeds).

Robert


[Modified by rwj383, 2:29 PM 7/21/2003]

 

I'm just guessing, but I think it has to do with compliance with emission laws and regulations.

 

Emissions :iagree:

 

Hot oil is easier to pump around the engine, so that when the engine runs hotter, the amount of power required to sit at idle goes down (at least until the oil break down and friction increases).

So, the whole engine runs hot to consume less gas than a cooler engine does--milage.

 

Pretty interesting stuff... thanks for the replies.

Sounds like all those ads for lower temp tstats claiming "more HP" aren't telling the whole story.

 

No they are not telling the whole story! The really big reason is in fact emissions! I say that and I am running the 175 degree T Stat, but then the car runs in the 180 to 185 range normally. Actually all the above reasons are there also. If I set in high temps she bumps up to the 190 range on hot days and crusing across the desert. Actually I was in Vegas last week and the outside temp was 110 and up. On the Mojavie I was seeing 124 outside air temps, and I was running in the 195 to 199 range. Got caught in traffic and had to slow down and saw 220 in stop and go traffic. but never hit the 230 level. I am also running the readline water wetter. On the average, I see a 70 to 80 degree temp differential between coolant and outside air, so I guess the system is working pretty well. Now the oil temp is a completely different story. I did not check the engine oil temp as much but it was in the 200s. The Trany was right up there in the 200-212 range also. (Hum need a trany cooler first! Remember that is driving in some extreme heat, and pushing it pretty good. running between 80 and 90 most of the way (except for the small traffic jam)

I think the message here is the cooler t'stat is fine as the engine will run warmer than that just due to fan turn on and outside operating conditions.

Jer

 

I think they make the most power when the coolant is in the 180 range.

 

Definitely for emissions purposes. Hotter running engines produce fewer emissions.

GM used to put lower t-stats in their engines (180 deg, if I remember correctly), and went to the 190 deg stats to achieve lower emissions, in the 1980's I believe.

I'm certain I read about this in one of GM's early tech papers.

 

smog laws :banghead:

 

As others have said hotter is less emissions which is also more effecient. With the C5's plastic intake air inlet temps are not really effected by engine block temp (plastic is a bad head conductor). I do not worry at all about the engine running 200 or 210.

 

Okay I'll plead complete ignorance here, regarding where a 180 or lower thermostat will help. I understand how cooler air into the intake helps, but not how cooling my engine below that of the stock thermostat will help.

I have the stock thermostat, and my coolant always reads from 192-194 while moving (highway/most city traffic) even in past two weeks of 98-100 degree weather in Dallas. Even sitting still in the heat, 205 is the hottest I've seen my coolant.

Engine oil temp under the weather same hot weather conditions is between 190-207 under highway or stop and go. If I'm really revving and running hard, it has gone up to 216-225 at the most.

My simple understanding has always been that it is good for the engine to heat beyond 212 so that condensation and other things in the oil can burn off. Is that incorrect? If so, does that have anything to do with engine oil being above 212?

What exactly does a 180 or lower thermostat do for a motor--both positive and negative. I'm curious as I don't understand how it helps, or is it hype?

Thanks,

Karl :confused:

 

I think C5s are designed to run hot to maximize fuel economy, minimize emissions, and extend engine life. I believe they need 194 degrees F to allow proper fuel control by the PCM.

Does anyone know the engine coolant temperature (ECT) specified in the PCM for the transition between "Open Loop" and "Closed Loop" fuel delivery?

Fuel is being provided in "Open Loop" when when the HO2S are not hot enough, or the ECT is below a specified (194F?) temperature, or a specified amount of time from startup has not passed.

Seems like running too cool a thermostat will delay/prevent the car from beginning "Closed Loop" operation. This would decrease fuel mileage and reduce performance, (Cause carbon build up?)

Are folks reprogramming the PCM when they change thermostats?


Reference: Page 6-1023 in the 2003 service manual.


[Modified by mapman, 12:58 AM 7/22/2003]

 

Laws are like rules...there made to be broken :)

:cheers:

 

I have a 160* thermostat and have changed my fan settings with the Predator. The coolant temp stays in the 175-185* range on even the hottest of South Carolina days. Maybe there is a good reason why GM wants it to be 25* warmer, but I just like it when my car runs cooler. I know just enough about metals and heat stress factors to know that the larger the heat differential is from 'cold' to 'hot' and back to 'cold', the more stresses there are put on the engine block, and I can put enough stress on it all by myself. :D

I have heard this many times before, and this isn't meant to be a flame, I just don't think it actually happens. While I agree that it would be beneficial to the engine if this were true, there are a couple of things to prevent it.

The oil system is a closed and PRESSURIZED system. If I remember right, my oil pressure is usually about 42#. According to my trusty steam tables here, at 40 PSIA water doesn't boil until 267.25*F. That means that your oil temp would have to get to about 275* or so for the watter to boil off in a 42 PSIG system. I don't even want to think about the 'physical property' changes due to the water being mixed with the oil, but lets assume that they are negligible as far as the point that I'm trying to make is concerned.

If your oil did get hot enough to 'boil off' the water into steam, where would it go? As the term 'closed system' implies, it isn't vented to the atmosphere. If you did manage to separate all of the steam from the oil inside your engine, it would probably just collect in 'pockets' that are in low flow areas and rob moving parts of proper lubrication. That would be a bad thing. :cry

While my above reasoning might be flawed, I don't think anyone can argue against the fact that oil floats on water, or that oil and water don't mix. That being said, if you NEVER drove your car, all of the water would eventually separate out of the oil and be sitting at the bottom of your oil pan. The next time you changed your oil all of the water would come out first (isn't gravity wonderful) and you could then refill your enging with 7 quarts of your favorite 'water free' oil. Unfortunately C5's are usually driven in a way that tends to 'mix things up' in the car. I can't imagine what a trip to the Piggly Wiggly would be like if I didn't have that cargo net in the back.

Anyway, I just don't buy it when people tell me that my car isn't running "hot enough" because of the 160* stat.
:cheers:

 

Great point, but from what I've read on this forum, even if you install a 160 tstat and adjust your fan settings, the temp still rises to 210 in city traffic... that would mean the temp goes from 160 to 210 (or so) regularly (50 degrees). With a stock tstat, the temp would only be going from 192 to 210 regularly (18 degrees). If that's correct, wouldn't the lower 18 degree temp differential be better for the engine?

 

The hotter they can make the engine run, the fewer emissions.

 

My understanding is a bit different than this. As far as I know the oil is not at high pressure in the oil pan and is only under pressure out of the pump and down the lines. (Think of a man made waterfall with a pump in the bottom of the pond) Also vapor is not stuck there as the crankcase is not a truly closed system as all vapor is vented to the combustion chamber by the PCV (positive crankcase ventilation system) In theory water will leave oil at any temperature as water will always evaporate, even at room temperature. What I, believe, makes this more difficult is the oil is always churning in a running car and tends to keep the water in suspension. Higher temperatures help seperate the water from the oil and once it becomes vapor it heads for the combustion chamber courtesy of the PCV system. That's my understanding, maybe somebody else can chime in.

 

I agree, but the lowest coolant temp your car will see (once warmed up) is about 10-12* above the thermostat rating due to radiator in-efficiency and the fact that you don't get any flow through the radiator at the point where the thermostat closes, so the coolant temp will never drop to the temperature rating of the stat. Last week I was stuck on I-20 in 90* heat and 90% humidity for about 45 minutes without moving at all, I had the A/C set on 68* in auto, and had nothing better to do than play with the DIC buttons. Much to my surprise, the coolant temp never went above 192*. That puts me in the 20* range category also, but only in extreme circumstances, in normal daily driving it stays between 175* and 185*. And before anybody brings it up, I normally have the coolant temp displayed on my DIC, and I usually switch it to Inst. MPG on long trips since the temp holds steady on the highway.

I didn't want to start an or anything, and I really don't know of any factual information either pro or con concerning a lower temp thermostat. I just wanted to throw in my concerning the 'boil off the water' reasoning. Like it's been stated before, the 192* stat (IMHO) is PROBABLY one of the ways GM got a 5.7L engine with 350+ HP to pass California emissions.