88 Formula w/305 TPI and A/C. 3 wks ago, the temp needle started bouncing - 220 to 240. Last wk, she hit 255, was ready to pull over, and back it went to 240. Did that all the way home (50 miles). Wired the fans so the 2nd comes on with the primary. No help. Is this the thermostat, water pump, bad temp guage? Anyone else seen this? I'm ready to tear into the stat this morning. Thanks.

 

Check the stat to see if its stuck. Then check for proper water pump operation by squeezing that upper radiator hose after the engine has warmed up and the thermostat has opened. Let go of the hose. You should feel coolant rushing by. The temp gauge is usually not the component that goes bad. Although it did in my car. Change the sending unit if you want to be sure. Its between the #1 and #3 cylinders and has a single green wire going to it.
bsa

 

You might even want to check for a bad radiator cap, it's cheap and can be cause of overheating.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER, NO CAT
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
3:73 Richmond Gears and 3" Exhaust
"There is nothing more addicting than speed"

 

Yeah man, might not be a bad idea to go ahead and replace the stat anyway. Mine stuck CLOSED once and the presure blew out my intake gaskets and my water pump gaskets. That wasnt fun.

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---Grady---
1984 Berlinetta.
LG4 305
Holley #1850 600 c.f.m. carb.
Edelbrock Performer intake.
TH-700R4.
Flowmaster 80 series/ 3" cat-back pipe.
Accel Superstock Coil.
7.5 10-bolt rear/ 3.08's.
Edelbrock Pro-flow air cleaner.
Pioneer head unit, Pioneer front 4X6's, Cerwin Vega rear 6x9's.
Daily Driver.

Personal Quote: "The Rice-Boys all tremble with fear when the old American V8 draws near."

 

I agree. A new thermostat is <$5, but if you don't have the time to get a new one, just remove the one you have and put everything back together. If the temperature returns to normal (or below normal), you'll know the thermostat is bad.

It happened to me once in the winter - got up to around 220° or more on the highway in freezing cold weather. Had to run with the heater on and windows down.

 

Does your car still have the air dam on it? My car never had one when i bought it and it used to get super hot on the highway but when i pulled over or was crusisng through town it would go back down to normal.

 

Thanks for all the tips. I started it up with the radiator cap off. Coolant was flowing immediately thru the system. Stat was stuck open. Replace that, but still hot. Found out the heater control valve was also stuck, and replaced it. Now my temp is at 190, which is 30+ degrees cooler that ever before. Bet I've been running with a bad control valve since I got the car 2+ years ago. Did a 200 mile run this week, 95 degrees outside, 80 mph all day long and still sat on 190 degrees. Guess I'll have to keep it now!

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1988 Firebird Formula, 305 TPI, K&N filter in 'hole-y' cannister, MSD coil and wires, Accel cap, Monaco seats