I have an odd overheating issue
it will run cool for a time 20 minutes or so and the heater blows hot air but all the sudden it jumps from 190 to 250 in less than a minute and the heater starts blowing cold.
Radiator is less than a year old.

so far I have

• replaced water-pump (twice just in case I got a bad one the 1st time)
• replaced thermostat
• ran with no thermostat
• flushed system twice
• checked fans
• temporarily wired fans to run constantly
• replaced radiator cap
• checked for coolant leaking into cylinders
• and a few other small things
• I did blead air from system each time

The engine is a high mileage engine but runs very strong and purrs like a kitten when idling.

no oil in water
no water in cylinders
no steam out tailpipe
no water in oil
coolant system has no leaks and holds pressure.

I gave up on it myself and took it to a very good mechanic and he is pulling his hair out trying to figure it out.

It does happen faster at high revs but will also do it idling.

It will stay cool if the radiator hose is off and fresh water from a hose is constantly running through it.

It started all of a sudden one day I stopped for a few mins and left it idling and it got hot and started blowing water out the plastic tank.
I let it cool off and refilled it and it ran 50 miles and overheated again.
I let it cool and refilled it and made it home but the next morning it was at 250 degrees in less than 10 mins.

anyone have any ideas?

 

Hey there

i had alot of problems last summer, and it was first summer owning the car. I can't even explain how bad it is.

Thing that can be bad:
-leak from a hose
-air in the system
-fans not coming up
-bad coolant reservoir cap

it can be a very small drip, and can make you a bad day, check hoses after a small drive if you can see anything.

Burping method(this has to be done before any new parts thrown in):

1. Fill the system through the surge tank opening.
2. Fill half the capacity of the system with 100 percent DEX-COOL® coolant. (ALTHOUGH RED COOLANT WORKS OUT GOOD.)
3. Slowly add clean drinkable water to the system until the level reaches to the base of the neck.
4. Start the engine.
5. Idle engine for 1 minute.
6. Install surge tank cap.
7. Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99°C (210°F).
9.Shut off the engine.
10. Refer to step 3 above to remove the surge tank cap.
11. Start the engine.
12. Idle engine for 1 minute and fill surge tank to 1/2 inch above COLD FULL mark on the radiator surge tank.
13. Install the surge tank cap.
14. Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99°C (210°F).
15. Shut off the engine.
16. Top off coolant as necessary, 1/2 inch above FULL COLD mark on the radiator surge tank.
17. Rinse away any excess coolant from the engine and the compartment.
18. Inspect the concentration of the coolant.


Do you hear fans in full speed at 235 degree? sometimes it can get a few degrees higher before they start.

My problem was first the water pump, it blowed totaly, after replace, air was in system and my cap blown down from coolant reservoir, changed cap(this caps can hold up to 15 psi pressure and more), did the burping system first day, had a drive, and the secound day, and everything went well for a month.

then, there was a small leak at heater core(i think that was the part) and again water blew out. bypased it with copper pipe. burped, everything was fine.


try your best and good luck

 

I agree. Also, check for debris blocking the flow of air through the condensor vanes such as a gazzilion tiny rocks. No air flow, it'll overheat. Verify that the fans actually run and insure its always both fans, not just one, using the hvac turned on. You most likely have a large air pocket trapped in there which is probably the source of your issues. Question: is your air-dams under the car still installed? They must be for things to work. Never leave the surge/pressure tank open...its a sealed and pressurized system and must be sealed for the system to work.

 

I would borrow anyone's scanner ( some auto parts store will loan their's for FREE) and check the ACTUAL ECT or coolant temperature--Most all scanners will read ECT in real time-
If in fact you have checked everything else--ran the fans on true manual-- seems likely the gauge is not working correctly

 

Thanks for the tips,
1. fans are working and double checked them by turning them on with a bypass wire to the relays in the fuse box.

2. I did burp it correctly plus the mechanic I took it to also did, he is not a shadtree guy and has a great reputation.

3. nothing is blocking the radiator fins, it is less than a year old plus I removed the covers and a used a water hose to clean it just to be safe.

4. it does not seem to have any leaks because it holds pressure good and I see no water and nothing looks wet and no steam from anywhere as would be expected if leaking at 250 degrees.

5. at this time I am only using tap water because antifreeze was getting expensive.

 

no she is getting hot. I can hear the water boiling and it did get hot enough to blow steam out the overflow tank

 

Your might consider checking the coolant for exhaust gasses. You can buy a test kit for this at any auto parts store. Gas in the coolant would be a head gasket. Do you see any bubbles in the overflow tank before it overheats?

 

Smells like head gasket is starting to go.shouldnt be long before she starts blowing smoke out da rear like a choo choo.had exact same symptoms.i mean exact and wasnt long after the gasket gave way..good luck

 

aww that doesn't sound good. but still better to figure the problem and solve it out then being stuck.

 

Ohh and i had to have heads resurfaced because my dumba$$ pushed it in red to get home.so i warped them almost to no repair.

 

Jeff, is the rad. new?

I've had radiators clog(guessing it was on the top RHS/small tubes), this would cause the EXACT same problems your are listing

the rad. looks fine, but the coolant tank would start to boil in 10 minutes, I replaced the rad. and all was well.

Steve

 

The ECT sensor might be defective, and may not be sending the correct temperature/resistance values to the PCM, or to a scanner readout.

I would measure the ACTUAL coolant temperature, at the surge tank, with a thermocouple type meter, or an accurate thermometer immersed in the coolant.

 

This is all I needed to hear; you have air in your system. Have you tried loosening the coolant crossover to see if you can bleed the air from the top of the motor? If your heater goes cold, then actual coolant flow has stopped also, usually due to an air bound pump.

I haven't ever done it on a Corvette, but on my old truck I can usually clear the air out by massaging the upper radiator hose, essentially turning my hands into a peristaltic pump and forcing the water to move through the hose. I don't know how stiff the hoses are on the Vette and if you can get to them easily enough to try this, though.

 

Any resolution yet? It would be interesting to know what caused the problem? Don't leave us hanging...............