C5 overheating! Temp fluctuating! Help
Thread Starter
4th Gear
Joined: Aug 2016
Posts: 4
Likes: 0
From: Kentucky
C5 overheating! Temp fluctuating! Help
New the the forum. Just bought my first corvette. A 2000 c5 5.7 auto. Went to clean it, washed the engine bay with a "engine degreaser" at the local car wash, really washed around the water pump etc. soon as I started it up it made a god awful noise. I shut it off, let it sit. Re started it, everything good, drove it all day and that night I noticed it getting hot. The coolant temp gauge was going from 200-250 up and down every few minutes. Twice it even went to 260 in the red, i pulled over and shut it off let it cool. Started it up temp started going down then back up and repeat. I checked the radiator and nothing it blocking it, could this maybe be a thermostat? Maybe a water pump? I'm letting everyone this cool down right now before I get into it. Gonna start by checked coolant level and etc. worries me because I had a Duramax before this and it done the same thing, it was head gaskets.. 
Melting Slicks
Joined: Sep 2011
Posts: 2,258
Likes: 543
From: Appleton WI
Since you washed the engine, you may have water in the electrical connections which could be giving you the erratic readings. Did the car actually boil over or was it just the gage indicating an over temp condition? You might take compressed air and blow out various connectors and let things dry out.
Melting Slicks
Joined: Sep 2011
Posts: 2,258
Likes: 543
From: Appleton WI
I don't know if a non working fan would cause the gage to fluctuate but it certainly wouldn't hurt to check. Also try turning on the heater when the engine is up to temp. Do you get heat. If yes, thermostat and water pump are working. Does the engine temp drop and stay in more normal ranges? If yes, could be pointing to the radiator.
I wash my engine a couple times a year. I don't use a pressure washer. I just use a garden hose. I use compressed air to dry things off a bit before starting the car.
I wash my engine a couple times a year. I don't use a pressure washer. I just use a garden hose. I use compressed air to dry things off a bit before starting the car.
Last edited by 3sACROWD; Aug 12, 2016 at 08:03 PM.
Thread Starter
4th Gear
Joined: Aug 2016
Posts: 4
Likes: 0
From: Kentucky
UPDATE: the coolant was low. I added some and attempted to cycle it threw until it got dark. When I left the car the tank was full. Now this morning looking at it it was almost empty. I tested the thermostat yesterday too and it opened around boiling point (my thermometer only went to 200). I filled the tank back up, drive it on Ramps and now under the car it's leaking antifreeze from the leaf spring (right under the water pump) I'm thinking it may be a water pump, I just got the car and the water pump looks really new. Is there a weap hole? If so where at? Should I pressure test the cooling system? And BTW when the car was warmed up yesterday I had no heat at all, the fans work though
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
A pressure test will tell you it's leaking - which you already know - but not where.
They make dye kits where you add due to the system, warm it up, then look for the dye under black light. Cheap, and works well.
They make dye kits where you add due to the system, warm it up, then look for the dye under black light. Cheap, and works well.
Advanced
Joined: Aug 2016
Posts: 85
Likes: 11
From: Boca Raton Florida
Check all of your hoses carefully, under the throttle body, around the thermostat housing, look on the underside of hoses with a mirror, you may have sliced a hose with the pressure washer, they get pretty brittle with age and heat.
Last edited by pgandy; Aug 13, 2016 at 11:28 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Melting Slicks
Joined: Jun 2002
Posts: 2,591
Likes: 144
From: Mobile al
Pull the radiator and clean the outer fins, I'm sure it needs it...these cars are literally vacuum cleaners, they suck up errythang.