I have serious doubt that this is the problem...'Cause....

a serious increase in RPM WITHOUT an increase in speed (airflow) gets you what?
the same air, MORE heat being generated. Yes, the pump may be turning faster BUT these pumps peak at a specific range so they are efficient across the board in performance meaning that its moving as much water at 2500 rpm as it is at 3500+. No significant improvement,
so again, whats left?
more rpm = more heat.

 

When mine is in good tune and I have the correct grade fuel in there, there is no difference in performance at 235 than there is at 180..
I will give this to the old schoolers tho, when/if something is WRONG, the higher the temps the MORE the problem tends to make itself known......

There are other reasons to run in the 200's...

everyone is suspicious of emissions reasons. THATS the least of it all..

14:7 AFR is optimum to produce energy out of gasoline. These temps make the most out of this science,.


AND OIL stays cleaner and lubricates better when its at or near boiling to burn off moisture that turns it acidic and holds contaminates that damage the engines internals. Materials (metals, shape & size)are designed to perform at these temps....
re: LT piston slap under the 'normal temp' on the dash gauge. Normal.

180 degrees is Old School thinking. Even though these C4s are approaching 30, they are late model technology in design. lean fuel controls, higher temps, electronic management of all the things that manage the AFR and exhaust.
The 1970 approach to this just does not work anymore. Things have changed...

 

Thanks for all the replies, guys!! Obviously, I need to clear some things up.

Yes, when I did the flush, both knock sensors were removed.

I have ZERO coolant loss, and ZERO odor of coolant whatsoever.

Yes, these temps have been verified with an optical thermometer, as well as a calibrated mechanical gauge with the sending unit in place of the factory sending unit.

I have NEVER had a check engine light, but I do have a code reader. It's an older (late 90's) OTC reader with a seven (?) line LCD readout. The software reads everything from engine data and trouble codes to HVAC, ABS, and airbag data.

The question I have is not if these temps are good or not, the question is how do I get them lower. I bought the car in 06, and at highway speed, it ALWAYS ran in the low 190's (summer) and upper 180's (winter). My goal is to get it to do that again. I'm not "old school thinking" that it should run at those temps. I'm thinking that it once ran those temps, and should be doing so now.

I probably am over thinking the solution a bit. I have concluded that it's restricted, but I'm at a loss as to where. It was mentioned that I could clean out the sumps in the block by pulling the knock sensors and spraying it with water. With the symptoms I have, that makes huge sense. Dunno why, but I haven't thought of that.

When I posted this, I had pretty much made up my mind that I was gonna pull the heads, but you have all been a big help and it looks like I have a few different avenues I can go before tearing it down.

I'll give everything a detailed once once over again, but looks like the next step will be making absolutely certain that there's no restriction in the block and go from there...

 

Back on post 13 I ask about the t-stat and programming, I don't see where you answered that. Are they all factory?

 

Yes. They are both factory. Thermostat is a 180* LT1 style thermostat, and the ECM is completely original with original programming.

 

As far as the debate on if it's better to run over 200*, all I can say is that my engine is noticeably noisier at 220* than it is when it's cooler. When idling, I can tell by the sound that it's much hotter than it needs to be. Obviously, this is a result of hotter oil, but that just doesn't sit well with me. Perhaps it makes a few horses at higher temps, but all I can say for absolute certainty is that it made more than I really needed when it ran cooler a couple years ago.

BTW, most of the reason for people like Joe Gibbs and his peers to find more horsepower at higher temps is strictly an aerodynamic issue. Car manufacturers like the idea as well so they can have a more aerodynamic car, as well as a cleaner running car since the higher temps make for a cleaner burn. However, the challenge has always been keeping an engine alive at higher temps. Metal will always weaken as it heats up, and iron and steel will always expand and contract at different rates as it heats and cools. The hotter an engine gets, the more it expands. Later model engines are better designed to handle this than an engine with an iron block / aluminum heads. There is considerable more expansion at 220* than there is at 190*, and since I'm making more than enough power at 190*, then that's where I plan to see my engine run at highway speed... Like it did a couple years ago. As far as running cleaner at higher temps, all I can say is that I change my oil quite often, and I could not care less about what comes out of the tailpipe since I'm not emissions tested, and I don't drive the car enough for it to make very much difference. It still gets respectable gas mileage, and has no codes, and it's cats and all emissions components are in tact and working just fine. Not to be a smart *** and / or offend anyone, but if I wanted "clean", I'd buy a Prius, but I just want my fun-as-hell Corvette to look, run and perform as well as the day it was made. No better, no worse. If I do decide to get a few more horses out of it, I'm damn sure not gonna do it by making it run hotter... Or cooler for that matter. I'm gonna get it to run the temps it was engineered and used to run. Adding power to an engine that's running hot generally doesn't work out well on an engine that was not designed to make power at high temps.

 

Put a fan switch in it that will help cool it, the problem isn't in the parts, all thou you might try and flush the system.

 

The system has been flushed several times. The fan(s) are not the problem. It's not cooling at 75 mph. Fans are of no use at that speed.

 

Unlike some of the other new Corvette owners, you do seem to understand what your car is "supposed" to be doing.
At 75 mph, you should have all the air flow you need going across the radiator fins.

You should not be seeing temps over 210°F at that speed.
Even though that temp will not cause any issues, you should only see those temps in stoplight situations.

 

Believe it or not, I've had a wrench in my hand for about 30 years. Cooling issues are nothing new to me, but this is the first car that I've ever seen that runs cooler when it's driven in a way that should make it run hotter. Every scenario that I've thought of that could possibly be the culprit, is a scenario that would make it run hotter, not cooler, I.E. head gasket.

Cleaning out the sump makes a lot of sense. It also makes sense because most Chevys would flow coolant to the block first, which, by design, would help keep sediment out of the block. The reverse flow would push the sediment to the bottom of the block water jacket and leave it there. I've obviously got a restriction, which is why I've focused as much as I have in the thermostat. I only replaced the pump in hopes that I had a bad impeller, but that turned out to not be the case. I was sure that the restriction, initially was in the radiator, but 2 radiators later, that's apparently not the case. It's looking now like the blockage in the block (or heads) was at least matching the restriction that the factory radiator had.

After some thought, and research, I'm still wondering the best way to clean out the block and heads. I have a hose adapter that will allow me to hook a garden hose to the upper radiator hose and run hot water, backwards through the cooling system with the tstat removed. If my problem is in the lower part of the block, then that's gonna be a bit more of a challenge to get that cleaned out. I'm not sure of a solvent that would help dissolve any corrosion or sediment that would be strong enough to do so without being too strong that it wouldn't damage the radiator, heads and / or gaskets. I might call around to some shops and see if maybe they have a way, or some kind of trick up their sleeve to clean the block without having to remove the engine. I have a feeling that this is about to get interesting...

 

I just went back and re-read all the replys has the airflow path been cleaned out ?

 

On a computer controlled EFI engine you canget more power by putting in a 160 degree stat, but only because the computer stays in an enrichment mode when the engine is below a predetermined temp.
A hot engine always runs better do to better fuel and air blending. I give 2 examples of this.
1. If you have ever really overheated an engine you might have noticed that at around 240 degrees that it ran like a watch.
2. Smokey Yunick built a hot vapor engine that heated the air fuel mixture to over 400 degrees, and the engine ran at around 300 degrees if I recall. It was in a fiero with a 2.5 liter 4 cyl. it put out 250 hp and got over 50 mpg.
My C4 with the L98 runs 200 plus all the time. The fans are set to turn on a 220 from the factory. On very hot days it has been at 215 to 220 for an hour or more in the city.

 

The a/c condenser was replaced along with the radiator. The air flow path is as clean as it gets.

 

It looks like we might have a winner. Dunno why, but I cannot find the original post that suggested that I pull the knock sensors, remove the thermostat and flush out and clean out the water jackets in the block. Today, I did just that. I even went so far as to dig around a bit in the holes the knock sensors screw into. I was ASTOUNDED at the amount of sediment that came out of there!! I not only back flushed it with the sensors out, but I did it with one sensor out at a time to increase the water flow through each side individually. Then, I used a blow nozzle to blow air into each side if the block, then flushed it again, which got more debris out if the block. After putting it all back together, and burping it like a new born baby, I idled it up to operating temp, which was about 10 degrees lower than it did before, which was about 197* with the AC on and the fans on. I then turned the AC off and let the temp go up to about 220*, then kicked the AC on, and it cooled right back down to about 200*. All that said, I haven't driven it yet. I just wanted to get a good heat cycle on it so I can make absolut sure that it's burped properly, but with all things being what they were after the flush, it is certainly encouraging. Seeing it cool off after heating up at idle is very encouraging. It would not do that before without hitting 3000 RPM. I'll post another update after I drive it, but I certainly believe, at this point, that cleaning put the block just might have done the trick :-D

 

Originally Posted by seabright (Deleted post due to the abundance of experts that didn't understand what you were trying to achieve i.e.: ....... 'getting back to your normal op temps' .... not accepting the 'new' higher temp as being OK, and there is no need for arguing on this forum.) (Thanks to bjankuski - post #20 - for his intellectual support)

Read your previous posts again, and it appears that lack of coolant flow may be your problem. Temp drops when you shift down a gear, which increases RPMs and coolant flow. This would leave one to deduce that there may be an obstruction in the coolant path.

Your 'flush post' didn't include removal of the two knock sensors. The knock sensors are located in the bottom of the block. Heavy contaminants will settle at the bottom of the block, which acts much like a sump, eventually building up, and restricting coolant flow. Flushing will remove contaminated coolant, but not the sediment in the 'sump'. Only by removing the knock sensors can you clean out the 'sump'.

Cleaning out the sump requires more than just removing the knock sensors and draining the the coolant. Water sprayed into the knock sensor holes is required (may take several applications for a thorough job.

If the knock sensors have been replaced, and the sediment removed...... I'm not much help.

 

Thanks for the comment.

 

its a lot of trouble, but if you can pull the freeze plugs, or at least some of the easier ones to get to, you can really access the cooling water passages for cleaning; just pulling the knock sensors, not so much.

 

also at 3000 rpm you my be richer which = cooler with the temps you are talking about you may be lean under light load and rpm range. if you don't drop to 3rd whats your fuel consumption look like. Whats your fuel pressure? temps are not always water related. Mixture and timing have a big effect.