jzbqwp

Hello all..
Please help where you can. 4 months ago overheated with symptoms of thermostat stuck so it was replaced and system burped per shop manual and ran at 204 degrees religiously in town. A couple weeks ago drove to work and it stayed at 230 . Drove it last week went to 256 and I freaked out pulled over waited to cool and limped home. Burped the system again to no avail, 250 and shut it off. Ordered Stant #45218 thermo and #10331 cap thinking one may be bad. Put the cap on, started it in the garage fans came on at 130 digital, and the analog was pegged. Bad thing, service engine light came on, no leaks, no white smoke, any ideas? Thanks for any help.

93Rubie

Pull the codes see what the CEL is.

96GS#007

If there are no external leaks, then it's typically a head gasket or a cracked head. The coolant has to go somewhere and if the path is small enough you won't see white smoke. In addition, if the aluminum heads have a crack, it's not unusual for the crack to leak when hot and seal/hold pressure just fine when cold.

zr1fred

And run a compression check, even without smoke you could have a head gasket blown or a cracked head. Check plugs for any difference in color, too.

Benny42

Before you dig too deep... is the water pump pumping?

jzbqwp

I will pull the codes after work today, will the paper clip method do the trick? Also, how can I determine if the water pump is functioning? Thank you all.

96 Vette CE

Take the radiator cap off when the engine is cool and start the car, you should be able to see the coolant circulating if the water pump is functioning properly.

desertmike1

Have you checked the front side of the Radiator/AC Condensor for blockage.. These cars are notorious for picking up debris.

Frizlefrak

Before I dug any further on any C4 overheating issue, pulling the radiator out and cleaning the debris off the front would be the first thing I did. These cars are road vacuums. If you've never done this, do it now. Even if it isn't the primary cause of your overheating, it probably needs to be done anyway, and it's one more thing you can scratch off the list. Take it to a radiator shop and have it flushed and pressure checked while it's out.

Your problem may just be a wal-mart bag the car inhaled.

jzbqwp

Ok I removed surge tank cap to watch for flow to see if the water pump was functioning , when it appeared to flow somewhat, I went around to turn it off, antifreeze boiled out of the neck

96 Vette CE

Sounds like you may have a stuck thermostat/waterpump failure. When the car is at operating temp, turn the heater on inside the car, is it blowing hot air? Cleaning the debris in between the radiator as mentioned is also a good idea, one of the first things i did when i bought mine.

Paul Workman

Sounds like the gang here has pretty much surrounded the usual suspects!

Summary:

Over heating, but does not require more antifreeze?

-Circulation?

Cold start with reservoir cap off: is there sufficient coolant (first off). As engine warms up placing a finger in the coolant, does the temp come up?
Is there visible circulation?
Does the heater produce warm/hot air? And/or are the heater hoses hot?
Do the radiator fans come on, and if they do, is the air warm/hot?

All of the above indicate at least some pump circulation, espcially the heater core.

Blocked radiator:

heater gets hot and there's good circulation visible at the reservoir cap opening.
Fans come on, but air is weak or not especially heated (external debris)
radiator air flow good, but little heat (blocked coolant tubes)
Dexcool (orange coolant) mixed with (green) glycol antifreeze (notorious for blocking coolant tubes!!!)
low air volume through radiator fans?
-cooling fans not coming on
-thermostat stuck or intalled upside down (rare)

A heat surge is common after shutting a hot motor off, as circulation stops with the pump not running, and engine heat will spike coolant temps. That is to say, some coolant boiling over an open reservoir went then engine was truned off would not surprise me. Some coolant. But, if we're talking a violent eruption of steam and coolant being expelled...that would be cause for concern...Or it would to me.

A head gasket leak would = coolant level requiring frequent topping off. And, foam on the dipstick the color of chocolate milk is a sure sign of coolant in the oil, as is the fluid level on the dip stick rising, as tho "something" had been added.

Head gasket leaks are almost always fore told by a spark plug that appears extremely clean and white compared to the others - almost like new clean. As mentioned, a compression test can indicate a gasket issue, as well as can a leak-down test.

A cracked block or crack in a head may not result in a clean spark plug, but the oil will be foamy.

Hope some of this helps. Good luck!

P.

anciano

That's pretty strange right there, both the variance in digital and analog readings and the fact that the fans came on at only 130 digital instead of 228-235. Maybe you meant to type 230. When the fans came on did they pull the temp down? If so, it sounds more like you have some problem in the temp sensors or fan relays than in the circulating cooling system itself. Erratic fan activation? If the fans are not coming on during slow speed travel or when stopped at lights the temp will soar quickly.

I put manual fan switches on mine and when I see anything north of 200 I flick 'em on. Even stopped and idling the temps come right down.

jzbqwp

Has required coolant after ran out surge tank neck, other times coolant went to over flow and back into engine when cooled. Was not a violent boil when shut off so i'm assuming heat spike for the reason.

No foam on dipstick, haven't pulled plugs (yet), only Dexcool no combo orange and green, thermostat in correctly, haven't checked heater for cold air (yet), fans coming on but the last time it was started they came on way too early 130 degrees yes 130...weird, going to pull codes as engine light came on, hopefully something got stored. Removing thermo to boil it for functionality. Thanks for every thing

LannyL81

Leave the thermostat out and run engine to see what the temps does.

I know....its a pain to drain some coolant, take thermostat out, replace coolant, burp...but it does eliminate one part.

jzbqwp

Pulled thermo and tested , it's good

desertmike1

"Meaning" engine ran Cool? if so,

zr1fred

A cracked head or bad head gasket doesn't necessarily mean loss of coolant or coolant in the oil untill later stages. Initially it will show up as overheating on long trips and/or under load. It will usually get worse. By the time you get foamy oil, the engine needs new bearings.

jzbqwp

Put everything back together yesterday "burped" it two times, got hot air from heater after second burp, temp at 203* for 10min idleing, did not drive it (raining). Refilled fluid started a third time, then at 190* engine surged or rpm went up and back down, fans came on and the engine light came on all at the same time. Code read H64, isn't that rightside O2 sensor? I had both sensors replaced over the summer. Seems to idle fine even with light on... temp still 203*, any ideas on that gremlin?

96 Vette CE

The "H" is a history code, stored from when you had problems with the O2 sensors.