The two summers I've had my 03, coolant temps stayed in the mid 190's, but got up to 225 in gridlock. Running 225-234 for two hours at highway speeds.... something's wrong. Your thermostat's open, otherwise temps would just keep rising. Sounds like the radiator could be the weak link - removing some, but not enough, heat. Stupid question, but I have to ask - have you checked for partial debris blockage on the air intake side of the radiator?

 

EHS, I've seen this same claim repeated many times on the forum and just couldn't imagine that we'd have to get up to 212 to release water from the oil. Water evaporates even when frozen (note old ice trays in your non-defrost freezer). The information I've found in the short crawl around the web came from aviation sources and they make interesting points. One of the most interesting is that oil temps in the engine aren't consistent. Oil that touches the cylinder and underside of the piston are far greater than that shown on the DIC. Other areas, understandably, are also higher in temp than what the DIC shows. That article mentioned an optimum oil temp of 180F.

A second article was an interview with an ExxonMobil General Aviation Manager regarding moisture in crankcase oils. Guess what oil temp he recommended....."Typically, you should operate your oil at 180-185 F. Maximum Oil temperature is usually 245 F."



Lower coolant temperatures = lower intake temperatures, also = lower incidence of hot spots in combustion chamber = reduced chance of pre-ignition = less KR = optimum performance = better fuel mileage = more HP = less wear & tear on the engine (pre-ignition & detonation play havoc in your engine). Also, lower coolant temps = lower ATF temps = better for the life of the transmission if you don't have a tranny cooler. Also, the flash of oil additives (both crankcase and oil) is reduced since the temps are lower which reduces build-up of varnish and sludge (not as important with Mobil 1, Amsoil, et al)

Somone will argue "carbon build-up." Well, we have top end carbon buildup with the stock thermostat, so what's the difference and no one can prove we get more build-up with a 160 t-stat than a 192, anyway. FWIW, rule of thumb is you get an extra 1 bhp per 9F drop in temperature. Worth it???? That's up to the individual. I like protecting my engine from knock and the crankcase and tranny lubes from thermal breakdown.

Rant Off.

I've had stock, modified stock, 180 and 160 H-tech stats. I'll keep my 160.

As far as the original issue of the post, lost in all the answers, I imagine the t-stat is faulty and may be opening, but not all the way. Happened in one of my other vehicles last year.

REMEMBER!!!!-----test your new t-stat, whatever temp, in a pot of boiling water with a cooking thermometer, monitor the temp that the t-stat opens and when it's full open. Make sure it opens fully! There are duds out there....you don't want to install a dud. It only takes 10 min. (or less) to check. It'll drive you nuts if you install a dud and then still have the problem. Don't forget to get all the air out of your system, too, to prevent engine damage (hot spots from no coolant).

 

Living in Dallas, I will most probably go to a 160. I never did a thermostat that was on the bottom of the engine, I'm used to them being on top - you don't have to drop all the coolant when they're on top.
Pardon the stupidity here, but should I drop the coolant first (is there a drain on the radiator??)?

And can you explain what/how to remove the air from the system?

Many thanks

 

 

Thanks topcat! very informative...

 

Well, just ordered a hypertech 160 t-stat and a bottle of redline water wetter from thunder. Should be here friday...will post results after its in.

 

1998 with 38000miles always 190. GM says 180 is just right, on older small blocks.

 

I rebuilt at 350 hours (for about $9,000) a Lycoming O-435 that used to run at 170 degrees all year round. The internal corrosion and rust was amazing.

I don't run it at that temperature anymore. Lesson learned.

 

Lycoming O-435? and where was the rust corrosion?

 

The Hypertech 160 T-Stat begins to open at 160 and is not fully open until ~178. My temps run consistently at around 190+.

 

Inside the block, under the pistons, basically everywhere.

The folks who did the rebuild said the problem was the airplane had an STC glider towing mod -- which included a modified cowling to give better cooling, but especially at high angles of attack.

The temps were always at the bottom of the green arc, i.e., 160-170 degrees -- I thought it was cool.

Turned out to be too cool.

As a matter of fact, I just thought of this -- here's a picture posted in another thread -- take a look at the oil temp (it used to run another ten or twenty degrees cooler). Also note the tach time:

 

The 160 degree thromostat is the best thing I did since installing 3.42 gears in my A4. They both have been in for about four years and I have no complaints.

 

How does lower coolant temps = lower intake temps, since our intakes are plastic, with no coolant passages?

 

Thank you.

I just couldn't face responding to that post.

 

Good question.
For one thing, it depends on where your air intake is. My post was long enough already and didn't want to elaborate, but since you asked.....a cooler engine = cooler underhood temps so one way is, if you have a Blackwing, stock airbox, etc., that draws the air from under the hood, under hood temps are lower w/cooler t-stat. One could argue that point, too, and you can increase airflow under the hood to reduce temps, etc., etc., but when you increase airflow through the car you increase aerodynamic drag which increases HP requirements at speed, and on and on. The second way is..... as the air passes through the intake port of the head, which does have coolant passages, as well as oil cooling, and as intake air passes the intake valve......the air is picking up heat all the way through. The piston surface and the combustion chamber in the head will be cooler (due to oil and coolant cooling, piston and head, respectively), so the resultant combustion mix temp will be lower (I know, not intake air, but following the flow path, thought I'd mention it).

If you have an aftermarket aluminum intake, you'll have heat soak through the intake and the heat will be picked up by convection cooling. The plastic intake is not a perfect insulator, so yes, you'll still get a small amount of heat from the plastic intake.....there's been threads touting the benefits of water injection and how their intakes are much cooler, which means they are above ambient....heated by the radiant heat from the engine and if the temperature difference is greater (212F engine vs. 190F engine compared to 120F????? intake) you have greater heat transfer to the intake from the lifter valley below (radiant heat) ......my plastic intake is black and black is a great absorber of radiant energy.

If you increase the temperature of air by 10F, you increase the specific volume ~2%, reducing the air density by ~2%, reducing the oxygen content, reducing the amount of fuel required in the combustion chamber for a 13:1 AFR, reducing the amount of power produced. The power adjustment isn't linear, so I'm not saying that in a 345 HP engine you'd get a 6.9 HP increase for every 10F air temp reduction, but I digress....you have to take into consideration ping, preignition, KR, etc. also consider the combustion mix temps (are they really higher or lower....if more O2 and fuel, couldn't it be hotter in the combustion chamber...but the coolant keeps it cooler??????) and is there less complete vaporization of the fuel with the lower temps causing more wetting of the intake port (one negative I can think of for lower temps in the engine), etc., etc.

We could go on and on and on and on. My main reason for a cooler stat is engine/tranny (auto) longevity by lowering operating temperatures (especially that of the lubricants). Any power increase is icing on the cake.

Upshot....for moderate climates (i.e., temperatures), I'm convinced a Hypertech 160F t-stat is the best choice, until someone proves me wrong. Then I'll gladly change my tune (pun intended).

Hypertech provides great instructions with their t-stat. The C5 t-stat is still on top of the engine, but fluid pours out when you remove it. There is a drain on the bottom of the radiator and you can collect and reuse your coolant if it isn't too used or too old.....cheap insurance to replace it, though. Use distilled water from the grocery store, not tap water. It's dirt cheap and it doesn't have minerals that can deposit on the cooling surfaces of the engine/radiator. If you're really quick and prepared, you can swap the t-stats out without draining any fluid. I can do it and lose about a cup to a quart, but it's tough. I found that if I pinch the coolant reservoir hoses closed, there isn't as much static pressure trying to push coolant out of the engine and the radiator when doing the switch. Here's something Evil-Twin posted a while back....I learned most of what I regurgitate from him:

Now, I still get coolant coming out of the closed t-stat b/c of a small hole present in the t-stat to allow a little flow....if there were no flow, the hotter coolant would take forever get to the t-stat, heat it up and cause it to open.....you will get some seepage. Hypertech says to heat up your engine to operating temperature with the cap off the reservoir. Let it cool, top it off. I go overboard and will go a step or two further. The next time I drive the car I'll remove the cap (slowly) when I get home and let it cool overnight, then replace it, to make sure I get all the air out.

When I changed my coolant, I disconnected the upper hose, held the opening higher than the radiator, and filled the reservoir until coolant was coming out of the t-stat, lowered the upper hose to make sure it was full of fluid, and then replaced the hose on the thermostat....this helped me know that most of the air was out of the system before I even started the car. I hate the thought of dry cylinder heads upon startup. I found that I didn't have to replace any coolant in the reservoir after filling this way. As a matter of fact, I had too much in the reservoir b/c I think Hypertech recommended overfilling a little bit to replace the air that's purged when following their instructions.

All right, this post is WAAAAAYYYY too long. If you made it this far, sure hope you gained some knowledge and it helps you keep your C5 in tip top shape!!!!

 

Oh, my Gaawwwdd, ....

 

LOL. No no no no....its,,,,,,Ohhhh,,,,,,Myyyy,,, ,,Gawwdd

 

Tag!!

Great information Topcat, thanks!!!!

 

Topcat, that last post of yours was insane ! But, nonetheless very informative!!!

UPDATE: The 160* stat is in as well as the water wetter. Here are my observations:
1. Coolant temps on the highway at 85mph are 172* to 174* .
2. Sitting in 80*+ stop and go traffic with the a/c on, it goes from 185* to as high as 210*.
3. "normal" city driving it hangs around 185*.

Soooo...in a nutshell I am very happy with this mod!!! Not really worried about corrosion due to build up of moisture in the crankcase...I mean c'mon, it has to be hot enough under those pistons to burn off any water, and plus the block and head are aluminum !! My oil temps are still about 10*-20* hotter than the coolant anyway...

BTW, on a side note, I wound up changing the stat halfway in between NC and GA in an Advance parking lot!!! The temps were getting to 250* and I wasn't in a hurry... All I needed was a 10mm deep socket, rachet, and a set of pliers...oh, and 2 gallons of dexcool. (just don't tell Advance that I left 2 gallons of antifreeze on their parking lot ...I mean, it didn't come pouring out of the block like it was possed when I pulled the stat or anything )

 

How did you lose two gallons? Should have been a quart.

Bob