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How hot is too hot?



Yesterday I left my '84 unattended and idling for the first time. I was nearby and could hear it running. It was idling for about 10 min when I started to hear the engine rpms fluctuating. I went to the car to investigate and saw the hood steaming and temp gauge at 284 degrees! I immediately shut the car off. The antifreeze reservoir was boiling over. The fan did not come on.

I let the car cool down to about 194 degrees and then drove it for about 30 min at highway speeds. Seemed to start and run fine. From what I can tell, head gasket and heads are still ok.

Question is, is 284 degrees hot enough to do permanent engine damage? When I drove the car after letting it cool to 194, the engine felt strong but didn't seem as "snappy" as before--but that could just be my mind playing with me.
I believe the stock setting for the fan is 226 degrees (someone correct me if that's not right). A chip and a 160 thermostat make a world of difference. Your fans would kick on at 176. It's a pretty good investment.
Good luck

oh yeah.....Welcome to the CAC:)

JT ZR-Won said:
I believe the stock setting for the fan is 226 degrees...

I couldn't find it in any of the books at my elbow here, but I got this from the Mid America web site's Q&A section:
The temperature at which the fans turn on is 226-235 from the factory and that is because of emissions reasons. Most cars will operate at 190-210 on the highway and will go upwards to 240 in the city.

Turismo,keep checking you oil to make sure there isn,t any anti-freeze in it.Thats really hot but maybe you got lucky if there isn,t any damage. Chuck
Luck O' the Irish

Checked the oil today, no antifreeze yet. Chuck, besides the head and gaskets, have you ever seen other engine components damaged by overheating in the 290-300 degree range? Pistons, rings, valves? From a materials standpoint, these components should be pretty robust, as long as the oil gets to where its needed.

Does the L-83 have aluminum heads (I guess I could check easily witha magnet, eh)?

What is the acceptable cylinder compression (psi) range for the L-83? I was running 150 psi before overheating--going to check what it is tonight (wish me luck).

Thanks--I need to buy a factory service manual soon!
Find the Primary Cause.....


There is a reason why your car overheated. You need to determine what caused the problem or it will happen again. I think the clue is that your electric cooling fan never came on. Remember, the C4 doesn't have a grill, the cooling air must come from underneath. Idling at a standstill will cause the coolant temperature to rise. When the temp reaches approx 232 the electric cooling fan should kick in and draw air through your radiator to begin cooling your engine. A simple check is to open the hood, start the motor and let it idle until the temp reaches 230 - 235, if the fan doesn't turn on you know what your problem is. BTW, keep your hands and fingers away from that fan.

It's a simple fix,
Yes, I found out the hard way that the cooling fan is inoperative.

I have never overheated any vehicle that I owned and it REALLY aggravated me that this happened to my new (to me) corvette. Damn PO never said a word about the fan either.

What I am most concerned about now is if I have damaged the reciprocating parts in the engine. Only the experienced will come forth with an accurate statement. This is why I am querying those who have experienced an overheat, torn the engine down and inspected for component damage. Thus far no one has responded.

Thank you for the suggestions.
Overheat Experience


I know you want to hear some words of reassurance.

Here they are: Your description of how the motor is running now indicates that everything is OK.

My son is a small block Chevy racer. He has on occasion overheated his motor under racing conditions with various results. There are different degrees of overheating. On one occasion he was watching the temp rising as he was getting near the end of the race. He was in the lead with one lap to go. The temp gauge was now over 250 and quickly rising. He decided to try and finish the race. When he crossed the finish line the needle was pegged at 300. That motor got so hot that it boiled out all the water and siezed. GONZO! Nothing could be salvaged.

Another time the radiator was unknowlingly punchured in an incident with another race car. He was losing water and the temp was rising. When he saw it rise over 275 he shut it down and came into the pits. Cracked both heads and gaulded a piston. The motor was rebuilt and racing again the next week.

The point is that the damage is immediate and usually obvious. Your motor is probably alright. You really didn't cook it. By driving it and cooling it down slowly you did the best thing possible.

WARNING: One thing you should never do is add water to a hot engine that has been shut down. That will almost guarantee something will crack.
Thank you for the reassuring comments Al. It helps to know and hear from those who have experienced similar conditions so that I have some reference to base by assumptions on. I have now come to appreciate the extremely controlled temperature conditions in which IC engines operate. Within a window of 70 degrees, you can have a perfectly running engine, or a steaming hot pile of useless metal.

Yes, it was my intent to reduce the thermal stresses induced by letting the engine cool to operating temp and then holding it there for several minutes. I was attemping to normalize any metal which may have been hot worked.

I still feel so much anguish over what has happened. I just bought this car. My mind is totally screwed now because I think that I will never have the same performace from this engine as before the overheat. The only was to solve my mind**** is to tear the engine down and inspect or rebuild if damaged.

This all came about because I was distracted doing a chore I had asked my "friend" to do and he HADN'T DONE IT!

Please excuse my attitude.
Turismo,I agree with greyghost.Drive the car and see what happens.Your engine has the cast iron heads they will take the heat better as far as warping goes.I blew a head gasket in my 88 while on the turnpipe by the time I noticed the temp going up and got the car off an exit the oil had a lot of anti-freeze in it.Replaced the head gasket and ran the car another 2 years before trading it in.I was running Mobil 1 in it and I want to think that helped.I use Mobil 1 in my 77 also now.Give it a little time before tearing into that engine. Just my two cents worth. Chuck
I owned an 84 w/4+3 for a few months. My ran hot as heck. Waiting in traffic or at a drive through was scary. Mine never hit 280+. But it did around 245 or so once. ****ed me off too!

I had to replace the fan relay because mine was flaky. At the same time I also replaced the thermal switch (in the cylinder head on the passenger side). The 84 has a single fan and is pretty straightforward. The relay and thermal switch cost about $35 at the auto parts store. Swap them both if its got high miles just to be safe. After that your computer is doing the rest.
You can jumper around the relay to force the fan on to verify that the fan motor is ok.

I still have my 84 Shop Manual with Electrical Supplement. If you're interested in it send me an email. It ain't helping me. The manual says that with 15lb pressure cap boiling point is 262. Fan should kick on between 225-235. It was never consistent for me.

I tried the Hypertech chip and 160 stat. Helped on the low end running it cooler when cruising quite a bit. It didn't kick in my fan until somewhere around 210 or so. Better than stock but I have a very low opinion of Hypertech chips in an 84. I never felt any performance improvement at all.

I couldn't find you numbers on compression tests, sorry.

If it runs OK, then as others have said the cast irons heads are in your favor. However, you may want to keep an eye on your intake which I believe to be aluminum. A leaking intake, into the crankcase, can lead to major problems with bearings and such. If you take the car off the road in the winter, you may want to consider removal and re-installation.
Your car, like mine, runs alot cooler when your are moving and it tends to heat up while standing still, but anything above 250 degrees is overheating. Check your fan to make sure it is comming on, change your stat to a 180 degree, flush the system, put some coolant in it and maybe some water wetter, and clean you radiator to make sure its not clogged. Hope this helps.

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