i took my LT1 for a drive tonight, didn't get far from home both temp displays abruptly began climbing into the 240 degree range, so i turned around and within the last 1/10 of a mile from my garage the digital read 255 degrees and the gauge was into 260 degrees, boiling into the overflow tank, and the surge tank coolant level still had coolant at the bottom. Prior to this the engine was running around 225, the hot and cold coolant transfer between the surge tank and the overflow tank was as one would expect, no boiling. It's been around 500 miles since i replaced the the factory radiator with a Dewitts Direct Fit single row and an AC Delco 12TH11D 180 degree Professional thermostat. Will appreciate your thoughts on this concerning experience.

 

My guess would be thermostat or water pump failure

 

I agree likely a water pump or related. Have you checked the oil for signs of head gasket failure?

I've heard mixed things about the running temps on these cars but my completely original system sits around 210 and only ever once got to 225 on a 95 degree day with ac on full blast.

 

Inside of hose collapsed

 

I would make sure the fans are coming on and at what temp, old hoses get weak and can suck closed, can pop out the stat and can boil it to make sure it's working , cap ,if the cap is going bad can be sucking in air ,these old C-4 hate air in the coolant might just be a bad cap ,sounds like well what is wrong with my C-4 overheating ,not easy on a C-4 ,my 93 ran hot warming up in the garage I replaced everything but the air in the tires $300.00 later fixed ,what was the problem .RIGHT .Hope yours works out better that my 93 .. I know guessing no air in the system just saying any variation in the cooling system on a C-4 they go crazy, just have to go slow till ya find the problem. The fix may be easy finding may not be .. It will let ya know when it's happy ..

 

Didnt you have the cracked water fill neck? Even if you are getting a small amount of air in the system, it will cause an overheat problem. Id replace the tank anyway... Verify you have coolant flow... Make sure you bleed the system properly as well. Verify your fans are also engaging, (you didnt mention that)...

 

Did you check and blow out your AC condenser when the radiator was replaced? The C4 sucks up road dust like a giant vacuum cleaner!

 

Hello Gentlemen,

Prior to my follow up to your kind replies, i have been reading on this topic, finding a wealth of information.

First off, engine cool, last night i bled the air from the two air bleed sites, LH side under the throttle body and RH side above thermostat.
I filled the surge tank to the neck. The overflow tank fluid was at the cold level.
As the engine came to temp, violent frothing began coming out the surge tank opening.
All large hoses were firmly distended with engine running and fluid was hot.
Heat in the cockpit coming through vents hot.
No overheating diagnostic codes were triggered.

My answers In order of comments:

@pltmgr I am going to replace the new ACD 180' stat with the new Mishimoto 160' stat tomorrow. Steady stream of coolant flowing through the lower line into the surge tank.
@OneRedVette There is no trace of coolant on the engine oil dip stick.My fans both turn on and run.
@signify How can i diagnose a collapsed hose? If i remove the hose, can i visually see the collapsed area?
@radar502 Both fans turn on and stay running. Old hoses collapsing >>> does tis occur on the inside of the hose and therefore unable to see a collapse from the outside? I did not notice any hose collapse on the outside. My radiator cap is a new ACD; i realize just because a part is new does not mean the part can be defective.
@81c3 Your point on the surge tank leaking air is well taken. Prior to this event, i had repaired the leak with JB Weld and prior to the JBW repair, even though the leak was miniscule i was not having an overheating problem. I will definitley take into consideration replacing the surge tank. There was steady coolant flow into surge tank from lower hose. Fans turn on and run.
@OldStingRay Yes, i thoroughly cleaned the AC condensor prior to istalling the new Dewitts single row.

My plan of attack tomorrow:
1. Remove and test the new ACD stat
2. Replace the new ACD 180' stat with the new spare Mishimoto 160' stat. Start engine and observe engine temp rising.
3. Bleed both valves, throttle body side and stat housing side.
4. I replaced the lower rad.hose with an Autozone Duralast when i replaced the radiator. Can i visually diagnose a collapsed radiator hose? Is it good practice to just replace all the passenger side hoses regardless? What are your thoughts on best radiator hose kit? My thought is stay with AC Delco.
5. fwiw, the coolant pump is not leaking. it was replaced new 7,000 miles ago. I am assuming because there is a steady flow of coolant entering the surge tank from the lower hose, that the pump is circulating fluid.
6. I understand the excessive heat of coolant would account for the violent frothing. I had left the cap off the surge tank as my intent was to observe for air bubbles and add coolant as bubbles burped out, as the videos i watched, there should be no excessive heat of coolant, just a gentle recirculation with belching bubbles if there's air in the system.
7. I have been looking up info to diagnose if the coolant pump is moving coolant, but not found what i consider to be a definitive answer.

IS THERE ANYTHING ELSE I NEED TO CONSIDER that i have not asked?

Thanks in advance and kind regards.

 

I keep going back to my 93 nothing looked out of place but in about 10-15 min it would start blowing water out the cap, I just left if off, hose collapsing can most of the time see that, if hoses are old and soft time for a change anyway, biggest thing is the state boil it makes sure it's working ,them do all you have on the list , to vent out the air I leave the cap off and just let in ideal it may take 30 min ya can tell when the air is out no mo bubbles but it might stop bubbling then in a few start back . the book says the rase the front of the vette up a few feet to force the air to the front for the motor says it will bleed better, I would save that for last, do what ya got on the list, the fix may be easy finding it may not .
I replaced my water pump Hi end one and very hi end state that fixed it checked the old pump seemed to be working fine and tried not one but three states nothing helped . This 93 is my 4th C-4 all at one time or another all ran hot, just have to go through the steps, the weird part is very rare ya really know what was really going on with it just have to hit on the problem and BAM stops running hot , GOOD LUCK .. One mo thing nothing weird about your C-4 this as far as I can tell this is the prossess ..

 

on the upper hose engine intake there is a small valve that is used to purge air out of the system, mine started to overheat after i changed the antifreeze, air bubble in the cooling system

 

i've ordered a used looking in good conditin surge tank. the orignal in the car had a pinhole repair that had been leaking again for some time. and now leaking pretty much the entire circumference of the neck. Once i have the surg tank replaced, i'l lwork on bleeding the system of air.

 

 

You do know water pumps fail even with little use but when i changed my opti my car never overheated although you could not turn the water pump shaft with Channellock's at all that was at 12000 miles. Did you use a after market WPump?

 

Thanks fot your reply. I see coolant being pumped into the surge tank, so i believe that indicates the pump is working. I'm taking my time with getting this air lock removed. A friend of mine has a vacuum tool designed to go on the fille neck opening, so next week we're going to use his tool AFTER i check to be certain my new thermostat is working AND i have replaced the surge tank which arrived this afternoon.

 

I'm following up from my post of yesterday. After continuing to familiariaze myself with the invaluable info in the FSM, i decided to give another go to getting the air out of the system. I followed the instructions in the Ower's Manual to bleed the system. Bled the thermostat and throttle body and i used a radiator coolant funnel. System cold, the overflow tank coolant level was at low level and coolant was filled to the neck of the surge tank. Running the engine, was able to burp out significant amounts of air, squeezing the passenger side lower hose. Replacing the cap, at an idle, temps rose to 226' and the fan turned on, cooledthings down and turned off at 220, and contineud cooling down to around 216. Encouraged, i went for a 48 mile test drive, ambient temp around 45 and operating temp was a consistent 169-170 degrees the entire 48 miles. i am running a Mishimoto 160' thermostat. What i am learning is to study the FSM, and Owner's Manual. Considering this is the first car that i have ever dived deep into, for me it is essential to develop at least a basic understanding of how my Corvette is desigend to function. And ask for help on tis wonderful forum. Also, i am lucky that my decades of motorcycle work transfer to working on my Corvette.

 

Glad to hear you found the problem.

 

@old stingray Thank you! my work would be much slower without the help of the amazing people on this wonderful forum.

 

Good deal these old LT-1 hate air, I have seen people go nuts trying to figure out, what is going on with my Vette, It's just the air, Glad it's fixed ..

 

Steve,your words of thanks are very much appreciated. A little acknowledgment makes replying to posts such as yours worthwhile. Thanks again.

 

@old stingray couldn't agree more with you. Heartfelt words of appreciation don't happen often enough., at least imho.