I HAD MY RADIATOR RECORED, FLUSHED ENGINE BLOCK, 160 F THERMOSTATE, NEW STAGE 2 Q-JET CARB, NEW NGK PLUGS AND WATER PUMP WAS REBUILT 2 YEARS AGO. THE CAR IS RUNNING GREAT EXCEPT FOR  THE WATER TEMP FLACTUATION. AFTER DRIVING FOR MORE THAN 15 MIN THE TEMP GAUGE STARTS TO CREEP UP, IF I REALLY HAMMER THE CAR OR RUN AT HIGH SPEEDS THE TEMP JUMPS TO 220-240, IF I GET TO A STOP OR AFTER A WHILE THE TEMP GAUGE DROPS DOWN TO 180-190 WITHIN 10-20 SECONDS OR IF THE CAR RUNS IN IDLE FOR A LONG PERIOD OF TIME THE TEMP STAYS AT 190. I INSTALLED A MECHANICAL TEMP GAUGE( I BELIEVE THATS WHAT ITS CALLED) I REMOVED THE SREW ON TOP OF THE INTAKE MANIFOLD AND PUT IN THE SENSOR AND RAN IT TO THE FRONT OF THE WINDSHIELD SO I CAN SEE THE GAUGE, JUST TO CHECK AND SEE IF MY SENDER OR GAUGE WAS INCORRECT. I TOOK THE CAR OUT FOR A RIDE AND THE GAUGE WAS DOING THE SAME THING, IT WOULD REACH UP TO 245 AND WITHIN SECONDS GO BACK DOWN TO 190. COULD IT BE AIR IN THE SYSTEM, MY MECHANIC WHO DID THE WORK IS VERY WELL KNOWN ALL HE DOES IS RESTORES CLASSICS, HE WANTS ME TO BRING IT BACK TO HIM FOR A CLOSER LOOK. COULD IT BE THE WATER PUMP NOT WORKING WELL AT HIGH SPEEDS, HOW COULD A ENGINE COOL DOWN THAT FAST. ANY IDEAS!

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ALL THE SEALS AND BOTTOM SPOILER ARE THERE. THANKS

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My 78 does the same thing that you have decribed.  I have a new Edelbrock water pump, front spoiler and new seals.  Maybe they are suppose to run at those temp.  No boil over so guess will just live with it, unless you come up with a solution, if you do pls let me know.

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Eddie

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I think with that severe of a temp change you may well have air in the cooling system. 245 is TOO hot for the engine!!!
The temp sender has to have water touching it to read correctly, so if there is air in the cooling system, it can cause the gauge to read like that, and fluctuate quicky....and run hot!
You may have a hose that is collapsing too...
I'd say take it to the guy and let him check it out before it turns nasty, and damages the engine.

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Like Joel said, check your radiator hoses. Make sure they are firm, and especially make sure the bottom one has a spring and it's in good shape.

The other possibility is your clutch fan

Hate to say Ditto - But Joel has the right idea - air in the system and collapsing   & John's mentioned especially the bottom one -with a spring. Check it out before 245 fries something

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THE BOTTOM HOSE SEEMED FINE WHEN THE RAD WAS PULLED OUT, THE SPRING LOOKED FINE. HOW WOULD I KNOW IF IT NEEDS REPLACING? MY RAD HAS NO RAD CAP ON IT JUST THE EXPANSION TANK. I STARTED IT UP TODAY AND RAN IT WITH THE CAP OFF OF THE EXPANSION TANK, WHILE STILL COLD AND RUNNING I DID SEE ALOT OF AIR BUBBLES COMING UP, I RAN IT FOR A LITTLE LONGER AND REPLACED THE CAP. TOOK IT OUT FOR A RIDE AND DID SEEM TO BE BETTER, STILL GOT UP TO 230 FOR A SHORT PERIOD AND WENT BACK DOWN TO 190-210. GOING TO TRY A COUPLE OF MORE TIMES TAKING THE CAP OFF. ANY OTHER IDEAS HOW I CAN GET THE AIR POCKETS OUT.  THANKS

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Your thermostat may be sticking.

One thing I always do when installing one is drill a small, 1/8" hole in the flat area around the center of the 'stat. This allows all of the air to get out when you first fill the system. Most new 'stats these days have a hole with a little restrictor in it for the same reason. I will remove the restrictor on those.
Also, when filling the radiator with a cooling system that is empty, always turn the heater control to "Hot", so the coolant will circulate thru the heater core too(if your heater core is still connected, that is). This keeps the air in the system moving, and easier to find it's way out.

Make sure your coolant expansion tank is mounted in the right location too, and the hose is not loose where it attaches to the tank and the radiator. A loose hose connection at either or both ends will allow air to be sucked into the system as the engine cools back down.


btw...air bubbles in the tank could mean air in the system, or...a leaking head gasket/cracked head...

Did you have this same temp issue before flushing the engine?Adams' Apple2008-05-29 19:15:10

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Joel Adams
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I HAVE THE HOLES ON THE THERMOSTATE, I HAD THE AIR BUBBLES AT FIRST BUT AS THE CAR HEATED UP IT STOPPED. THE ISSUE I HAD BEFORE WAS THE TEMP WOULD RISE AT HIGH SPEEDS, MY RAD WAS 35% PLUGGED SO I RECORED IT. AFTER ALL THE WORK I DID AS I MENTIONED ON MY FIRST POSTING, NOW IT CREEPS UP QUICKLY AND AFTER LESS THAN A MINUTE IT WILL DROP BACK DOWN 40-50 DEGREES IN LESS THAN 15 SEC, IF I LET IT IDLE FOR A LONG PERIOD OF TIME IT DOES NOT MOVE BEYOND 190. IF MY HEAD GASKET WAS GONE  I WOULD BE LOSING COOLANT BUT IM NOT, IF IT WAS A CRACKED HEAD WOULDNT THE TEMP STAY HIGH FOR A LONGER PERIOD OF TIME, IT SEEMS TO COOL TO QUICK IF THE TEMP WAS THAT HIGH.

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Here is a pic of my engine compartment. Is your over flow tank in the same location?Hope this helps.



(large image modified to link)Adams' Apple2008-05-30 05:21:28

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"It Takes A Little Longer To Do It Right"
"It Takes A Lot Longer To Do It Again"

My '78 is still doing this same thing after new radiator and other stuff. Up to 220 - 230 then back down to just under 200. Just replaced the thermostat, no change. Darn, I think I'll pull it out this weekend and drill that little hole and see what happens. Should I stick with a 195 or go with a lower one?

A tip on thermostats...When I replace a thermostat, I always check it before I install it. Submerse it in a pan of warm water and bring the water to a boil and watch how the thermostat opens. Fish it out of the water, carefully!!!! and do a quick measurement and see if it is opening as far as it should. If not, exchange it where you bought it until you get one that is working correctly...took three attempts once to get one that worked right for a VW Rabbit! Unfortunately, I have not replaced one on the Corvette, so I don't know how far it should open.

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There is no substitute for low end torque!

WAS OUT OF TOWN, I WILL BE  BRINGING IT IN AT THE END OF THE WEEK, KEEP YOU GUYS UPDATED ON WHAT WE FIND WITH THE TEMP ISSUE!

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DID A PRESSURE TEST ON ALL THE CYLINDERS AND NO SIGN OF HEAD GASKET LEAK OR CRACKED HEAD. GOING TO CHANGE WATER PUMP, THE SHAFT HAS SOME PLAY AND IS MAKING A LITTLE NOISE, I HOPE THIS RESOLVES THE PROBLEM, KEEP YOU POSTED.

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CHANGED WATER PUMP AND NO CHANGE, WHAT DO I DO NEXT?

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LOOKING AT MY CORVETTE OWNERS MANUAL IT STATES THAT NORMAL OPERATING TEMP IS 210 AND HARD DRIVING OR AT HIGH SPEEDS 220-230 IS NORMAL. DO ANY OF YOU OUT THERE RUN AT THESE TEMPS. HAD IT OUT TODAY AFTER CHANGING THE WATER PUMP, RAN IT IDLING FOR 25MIN IT HIT 205, TOOK IT OUT AND STARTED TO HAMMER IT A COUPLE OF TIMES IT HIT 220-230, TOOK IT EASY ON THE WAY BACK WENT BACK DOWN TO 210. MY MECHANIC IS TELLING ME IT SHOULD NOT RUN THAT HOT, HE HAS DONE ALL THE TESTS  ON THE CAR AND IS ALSO BAFFLED. THE OWNERS MANUAL SAYS THIS IS NORMAL.

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Do you have a front license plate on car? Had to remove mine because of overheating at higher speeds (75-80+). Sounds exactly like what mine was doing.

RAISED THE FRONT END OF THE CAR, REMOVED THE CAP ON THE EXPANSION TANK, RAN IT FOR A GOOD 45 MIN. FILLED THE EXPANSION TANK 3/4 FULL, I HAVE TAKEN IT OUT NUMEROUS TIMES IN HIGH HEAT AND SHE RUNS AT 190, HARD DRIVING OR AT HIGH SPEEDS IT MIGHT REACH 210, MUST HAVE BEEN A AIR POCKET! I LIKE TO THANK EVERYONE FOR THERE HELP1  

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Hey JC,

WOW..... Glad it was just an air pocket!

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"It Takes A Little Longer To Do It Right"
"It Takes A Lot Longer To Do It Again"

Glad ya got it figured out, Jimmy!! Whew, eh?
I can't believe the owner's manual would state that 230* is "Normal"!! Wow...that's just too weird....
Anyway, glad she's runnin kewl now!!

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Joel Adams
C3VR Lifetime Member #56    
My Link


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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"