Hello, I am looking for some guidence/experience. I have a completely stock/original 72 corvette 350/200hp manual trans vehicle. I have just finished an under the hood restoration (painting, new hoses and such). The car has a 180 deg thermostat, but runs consistently around 210 deg. The timing is set at 8 deg at 800 rpm as per emissions sticker and the TCS system is hooked up and functional. This seems quite warm. After shutting the car off from normal driving and waiting a few minutes (ie gas station), and I restart the car the temp is at or near 250 (near the red line). Is this much "heat soak" normal? I previously owned a 1973 350ci car and the temp Aways stayed at 180 deg. Is there something I am missing? The radiator and engine have had a complete flush and all componenets are new-hoses, heater core, thrmostat etc... The radiator is the original Harrison aluminum unit. I have been told that if I disconnect the TCS system thus alowing vacuum to advance at all times that it will run cooler, but the problem is that if i run straight manifold vac to the dist, the idle is too high and cannot be backed down enough with the idle stop screw. I was told by the guy who restored my carb to OE spec that this is normal, as they liked to leave throttle plates slightly open at idle to allow extra airflow at idle thus reducing emmisions, and that retarding timing at idle compensated for this. Any experienc out there?

 

Is there a ported vacuum source on your carb? You could connect the vacuum advance to that without affecting the idle. I would also check the engine temp with ai IR gun to see if the gauge is correct.

 

First, the TCS system was designed to make the engine run hotter which burns more hydrocarbons so that is true. This is an emissions concession.

Second, do you have an idle stop solenoid? It was used to prevent dieseling or engine run-on. The idle stop solenoid pushes against the throttle linkage from the front. It requires a different way of starting the car as outlines under the lid of the battery compartment door.

First you turn the ignition key to the on position but don't start it, press the gas pedal slightly to allow the solenoid to extend, then start the engine.

Your normal idle speed is set with the solenoid not the idle screw. The minimum idle speed is set with the idle screw and the solenoid de-energized to about 400 rpm or the lowest rpm the engine will still run at.

Then you energize the idle stop solenoid and set the idle speed by screwing the plunger in (clockwise) to slow it down or out (counter-clockwise) to speed it up.

When the car is shut off, the solenoid retracts causing the throttle blades to close completely preventing dieseling.

By the way, I don't know about the small block but the big block thermostat is a 195 degree unit from the factory. Also an emissions concession.

cc

 

My car normally runs at 180-190, even on a hot day. When I stop for gas, and restart the car, the gauge does read higher for a short period of time, like 210-220. IMO, this is not only normal, but unavoidable if your gauge is working properly and is reasonably accurate. I don't like the term "heat soak", because so many people attribute so many different definitions to a term like that, but the reality is that your block and heads are hotter than your coolant, that is why heat is being transferred from the block and heads to your coolant. When the coolant stops moving, the block and heads will continue to transfer heat to the, now stationary, coolant until it is the same temperature they are.

What I would be more concerned with would be how long it takes for my gauge to get back to its steady-state temperature, whatever that may be. I often fill my tank at the end of a cruise, and the gas station I go to is about a mile from my house. By the time I get home (2-3 minutes tops), the coolant is already back to its normal 180-190 temperature. If it took more than a few minutes to return to the operating temperature, I would be concerned about a low-flow condition in the cooling system.

 

Tank you CC and PK,

CC, I understand the idle stop solenoid function and how it should be set to prevent run-on, but for the short term, after carb installation, I have it disconnected (with the intention of setting it up as you mentioned after all other bugs are worked out). The problem is that even with it disconnected the idle will not go below 850-900 with screw all the way backed out. So, if I were to run vacuum to the dist at idle (disconnect TCS) it would idle up to approx 12-1300. So, that is not an option to help it run cooler. Any other ideas, on why it runs at around 210 with a 180 thermostat?

PK, it sound as both of our cars temperature "climb" (about 30 deg) is about the same after shut off, it is just that yours starts off at a lower temp, thus does not approach the 240-250 mark. Maybe I should verify the guage ?

 

Do you have all the seals around the radiator and shroud?

RE: idle speed, did you check the choke to make sure it is set correctly and not stuck? Something has to be keeping those throttle blades open.

cc

 

i am about half asleep so i may have missed it but also the timing is set to make the engine run hot as well. they retarded the timing.
look up the sticky on timing and find where the engine runs best if it is set to be about 32 degrees at 3000 rpms. that will put your initial timing about twice what it is now.

 

Good point baxsom, I forgot about timing...I'm running 12 degrees initial on my big block.

He's running 8 degrees but I think 16 might be a little too high.

cc

 

Here's my 2 cents worth.
According to my Genuine Chevrolet Corvette owners manual, all engines use a 180 degree thermostat.
Could you possibly have a carburetor vacuum leak, causing a high idle rpm? If so, this could also cause higher temps.
Shooting it with a gun, should give you a better idea of the real water temp, maybe a bad temp sensor, guage.
Does it crank hard after stopping the engine for a short time?
Do you have all the seals installed around the radiator, this is a must?
Good Luck in your search.

 

djrammer, I checked my 1972 owner's manual and the section that describes the thermostat does not say anything about a temperature rating.

However, I looked in the 1972 Chevrolet Chassis Service manual and it has a section describing the 195 degree thermostat but there is nothing about a 180 degree thermostat. Also, the Emissions Label also calls for a 195 degree thermostat.

cc

 

The only reason for keeping a 195 deg. stat in an early 70's C3 is that you want to reduce hydrocarbon emissions at idle/low speed cruising. Other than emissions, 195 degs. does nothing good for your engine: is wastes fuel, it puts more wear on the engine, and it puts more heat into the cabin [regardless of the cabin insulation system you have]. Later year cars with computer systems would not function properly with a 180 deg. stat, as it wasn't warm enough to signal proper running conditions for the computer. Your car doesn't have that limitation. Put a 180 stat in the engine...it will thank you for it.

 

Well......... I've owned my '72 since it was new. All of the advice here is terrific. If you've followed all of it and still have a higher temperature than you're comfortable with, replace your stat with a 160 degree unit. I've been running one since I removed the original 180 degree stat (which I still have somewhere in a box) and my engine loves it. I have the 350/200hp base engine with 4speed, no a/c or air, no p/s or p/b. I'm up to 59,000 miles and looking forward to many more years and miles. Good luck!

 

Putting a 160 stat in your engine won't hurt anything. Chances are that once the engine stabilizes at operating temperature, it will be higher than 160 anyway...so the stat will be open all of the time and not really regulating anything. But, it could keep temps down a bit if you are having hi-temp problems. When I lived in AZ, I put a 160 stat in so that it would take longer for the engine to heat. It did help some...especially on those 112F summer days when I needed the A/C on, also.

 

I'm wondering if the clutch on the fan hasn't retired.

 

To check the clutch on the fan blades... Run car to get it up to normal temps; if you have A/C turn it on too. When ready, pull the car over and open the hood. Now, stand just outside the driver's door so you can watch the action of the fan. Turn the engine OFF and count (approximately) how many revolutions it takes for the fan to stop turning. Since the fan clutch is already HOT, it should be fully engaged and it should only take a couple of rotations for it to stop. If it goes more than 3 full turns after shutting the engine off, it probably should be repaired or replaced.

 

I also have a ‘72 with a BluePrint 383 that seems to exhibit a similar problem, although my gauge doesn’t jump as high (it also reads at 15 degrees hotter than actual temperature at warm up as measured with an infared gun). I had just installed a Standard brand temp sensor that I purchased at one of our shop suppliers , as the car didn’t have one when I purchased it. I used a vacuum type cooling system filler that I had at the shop. This system eliminates trapped air in the system. I also have a new aluminum radiator installed with electric fans. I’m suspecting the problem is in the new sending unit location. I had to install it in the intake manifold. The correct location is in the cylinder head, but the thread diameter there is too small. Supposedly they do that because of a combination of things. Later cars had smaller diameter temp sensors. And aftermarket gauges also are smaller, although every one I’ve seen comes with an adapter so I don’t understand that. I have not been able to find a smaller temp sensor that measures the same resistance required to make our temp gauges read accurately. As a last ditch effort I have just ordered a new temp sensor from Ecklers just so I can eliminate the possibility of a defective or wrong sensor. If there is no change then the problem has to be either the sensor location, or the gauge itself. I hope this helps you.

 

I actually sent that post to another thread, but it seemed to apply here as well. Good old copy and paste

 

LOL I've always wondered how to test one without damaging a fan blade or cutting my hand off. I always just replaced them if I was unsure, LOL. I wish you'd told me this 40 years ago.

 

Having dealt with "overheating" problems on both my 57 and 72, my advice is: Don't make any conclusions about engine temps based on the temp gauge in the car until you have verified it's accuracy with an IR gun. I spent a lot timing sweating (get it?) overheating problems until a cheap (under $20) IR gun off Amazon showed everything was actually perfectly normal. My 72 gauge says it is 205 idling in the hot sun on a 90 degree day, but my IR gun shows the engine and upper radiator hose say it is a comfy 178 degrees.