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C4 and C5 Coolant Temperatures...


Gone but not forgotten
Jan 30, 2001
Hermosa Beach, CA
1987 Z51 Silver Coupe
This was in the new America's Sportscar:

C4 and C5 Coolant Temperatures
by Jerry Watts

This doesn't seem to be the time of year to be concerned about coolant temperature, but running too cool a coolant temperature can also damage your engine.

Although the standard 180° thermostat is ideal, some Vette owners have been tempted to switch to a 160° thermostat. The lower temperature thermostat will result in uneven temperatures throughout the engine, causing unnecessary wear.

The average coolant temperature for a C4 or a C5 is around 205°, but even 230° is not a cause for concern since temperatures must reach 212° and 228° before the cooling fans come on. It's not until you get close to 250° that you need to be concerned, since boiling occurs at 262°.

_ken :w
Thank you for the great information!

I usually run at around 185-190 with my K&N in there. I did notice that after stopping in traffic, the temp. would drop much faster since I installed the K&N. And I never run the car unless coolant temp. is a minimum 150 or 170 in cold weather situations.

What is the ideal oil temp?
With all due respect to Jerry Watts I don't see why the 160 would cause uneven temps if the 180 won't. Is this temp "ideal" for the C4 or the C5. It seems that the ideal temp for an aluminum block would probably be different from an iron block. The only problem I heard Gordon Killebrew mention with a cooler thermostat was that the oil doesn't get to a high enough temp on short drives to evaporate the water and other impurities. But with Mobil 1 and changing oil and filter every 3K that doesn't seem to be too much of a problem. I've been running a 160 degree thermostat with HPP programming to turn the fans on at temps comenserate with the t-stat for the last 25000 miles and have seen no problems that would point to excessive wear on the engine. Just my .02.
The Tempature is Rising

Internal combustion engines will actually produce more power @ higher net water/combustion chamber temperatures. It promotes better internal combustion. What you want to lower is intake air temperatures to promote volumetric efficiency. The benefit of the 160 degree T Stat is that it tricks the processor into believing the engine is in the warm-up mode. The processor then lengthens the fuel injector on time & duration. This helps top end speeds some, at the cost of overall reduced fuel economy & engine longevity. When the engine is running around in closed loop which can happen with a 160 T Stat the raw unburned fuel will find its way past the piston rings & remove the thin film of oil which coats & protects the cylinder walls. This also leads to sludge build up.
Most racing teams F1, Indy, Etc. run their engines at a pre determined optimum temperature 210-230 degrees would be close. They keep the temperatures on the ragged edge to take advantage of all the horsepower/torque. There will not be a problem unless the coolant boils.
Re: The Tempature is Rising

Burnnrubber said:
Internal combustion engines will actually produce more power @ higher net water/combustion chamber temperatures. It promotes better internal combustion. What you want to lower is intake air temperatures to promote volumetric efficiency

The problems here are (1) higher water temp = higher intake air temps, since the intake plenum etc. gets heated by the engine;
(2) higher water temp = higher oil temps, and oil life is cut in half for every 20 degree F increase over 160F;
(3) Jerry Watts doesn't think 230F is a problem because he's not living in Texas or paying the repair bills for my engine!

If 190F thermostats were such a great idea, the automakers would have gone to them long before emissions requirements forced them to. High temp thermostats, and the resulting hotter combustion chamber walls, mean lower unburned hydrocarbons: that's the beginning and the end of the reason for high-temp 'stats.
Yes & No

1) Your exactly right, I suppose you could do the old drag race Mod. & block the water ports off in the intake while you are putting in the low temp T-stat.
2) Change your oil as required, as your going to really need to with the lower temp T stat. (Fuel/oil contamination)
3) Your right again..
4) The reason they produce less Hydrocarbons is because there is more complete combustion & hence more power avaliable. Way back when in ought 2 when they ran those 160-180 Deg, T-stats the automakers could not control the Air-Fuel ratios nearly as close as they can with micro processors (Read Fuel Injection).
I put a 160 thermostat in my Vette 2 years ago at 98,000 miles. It always runs 105 degrees over the outside air temp, so around here in the winter my engine runs 155 to 158 running down the highway. I got a oil cooler, which is cooled (heated) by the engine coolent so my oil temp runs right with the engine temp in the winter. No problems so far and I've got 120,000 miles on the car now. It still makes me nervous. Probably should drop in a 180 degree stat each winter.

I've seen no change in mileage, still 26 on the freeway and 14 around town. Got it up to 16 when I drove like my 75 year old mother for 2 days after I got my last ticket. :t

The biggest benefit I've seen is now my throttle body doesn't get sticky like it did with a 190 stat.

There is one more small point: with higher combustion chamber temperatures, your engine is just a little more inclined to detonate, so it's a little more sensitive to fuel octane level.
With the knock sensor looking out for you and dialing back the spark as required, you'll never notice the loss of horsepower - until someone running the 160 'stat pulls up next to you!
Read the Pump

If you would have selected the correct nozzle at the gas station (92 octane) you wouldn't need to worry about that guy with the 160 Deg T-stat. He would be so far behind you it wouldn't matter.
Well, I'd have been talking about an apples-to-apples comparison.

More specifically, L-98's will run more spark with more octane on up to about 110 Research octane, equivalent to maybe 98 - 100 "pump" (R+M/2) octane rating. And with an L-98 at least, more spark = more power. About 260 - 265 HP being possible with no other modifications.

What this means is that the cooler engine, less inclined to knock, will make more power.
the way I understand it is since the LT1/4 use reverse cooling, The cooler water going to the heads first results in a denser fuel/air charge. Supposedly this was the reason for the reverse flow modification anyway. Seems to me cooler heads=denser f/a charge=more power. Otherwise why use a cold air induction system.
I have trouble with absolute statements like "180 degree thermostat is ideal for C4 & C5". We are talking about the 180 being Ideal for a L83, L98, LT1, Lt4, LT5, LS1, and LS6. Does this mean that one size REALLY does fit all? :confused
cooling knowledge for c4s

Ken said:
;) [/QUOTEi to am running a160 stat and ihave modified the cooling fans to run at the same time.the fans come on at 195 and shut off at 170 or so.the ony down fall is heat,its there but its not sweat you out of the car hot.but what a difference in performance and summertime dependability.besides the factory setting of 232 is real close to steam,(not good). if you or anyone else is interested in how to controlboth fans go to (corvetteforum.com) and go to c4 tech tips.if its not there let me know i will type it out.
The real problem with the factory cut-in temperatures for the cooling fans is not so much the water temperature, but the A/C head pressure. At least here in the South, A/C head pressures quickly reach the point where the torque required to turn the compressor exceeds the torque developed by the A/C clutch, if the ambient temps are over about 95 - 98 F -- which happens often!
Helloooo, GM, is anyone paying attention to conditions OUTside of Detroit?
Sure, the 'puller' fan comes on when the A/C's on, but when the ambient is over 95F both fans need to be on, regardless of water temp. Having replaced three A/C clutches before I figured this out (OK, I'm a slow learner...), I think I know whereof I speak.
One solution, and I know it's not for everyone, is to use your existing relays and wire them to a toggle switch. Whenever the ambient temperature is up, and/or whenever the A/C is on, you flip the switch.
A fringe benefit of this is improved A/C performance in slow traffic.
- R
Electric Water Pump

Has anyone looked into electric water pumps?

I'm not sure where I read it, (I was surfing at a rapid rate, saw the comment, but didn't register it as important until I couldn't find it again...:hb ) but it claimed the following for an LT1:

1. Standard water pump flow is maximum 22 GPM at 6000 RPM.
2. Electric (don't know model/manufactured) provides 25 GPM at all times.
3. Reduced load on engine (MO POWER to the wheels)
4. Can leave pump on when the engine is shut down.
5. The standard electrical system can handle the load.

Does anyone have information on these?

What? Where? How? How much?

Next time I'll slow down a bit and get it myself.


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