Temp gauge not accurate?
Thread Starter
Race Director
Joined: Dec 2005
Posts: 13,515
Likes: 11
From: Fisher, IL
Temp gauge not accurate?
I just got my 69 and haven't dealt a whole lot with it yet.
I'm upgrading the suspension and right after that i'm going to dive into the cooling system.
I noticed the few times I drove it around town(10min trips usually) that the engine felt somewhat hot but the temp gauge showed only 115-150degrees. I know it moved so it's working somewhat right? I only judged how hot the engine was by opening up the hood and putting my hand near and comparing that to other cars i've done that too.
Is there a way to tell how hot the engine gets some other way? Or where do I start trying to fix the temp. gauge?
I'm upgrading the suspension and right after that i'm going to dive into the cooling system.
I noticed the few times I drove it around town(10min trips usually) that the engine felt somewhat hot but the temp gauge showed only 115-150degrees. I know it moved so it's working somewhat right? I only judged how hot the engine was by opening up the hood and putting my hand near and comparing that to other cars i've done that too.
Is there a way to tell how hot the engine gets some other way? Or where do I start trying to fix the temp. gauge?
Last edited by PUNISHER VETTE; Apr 9, 2010 at 04:36 PM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I have an IR gun that I shoot at multiple areas of the engine to determine the temps. They are never going to be 100% accurate but should be close. My gauge shows about 190 and I can shoot the engine and it usually is around 185 or 190ish it multilple places.
CF Community Team
Joined: Oct 2004
Posts: 19,357
Likes: 5,242
From: Cape Cod, Mass.
2025 C6 of the Year Finalist - Unmodified
2025 C8 Z06/7/E-Ray of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2021 C8 of the Year Finalist Unmodified
2020 Corvette of the Year Finalist (performance mods)
2019 C1 of Year Winner (performance mods)
2017 Corvette of the Year Finalist
2016 C2 of Year
2015 C3 of Year Finalist
The upper radiator hose near the thermostat housing is a good place to shoot it. Raytech mini temp is a good IR gun. They are cheap on E-Bay. Many uses. I just shot the lake out back, 51 degrees 
Thread Starter
Race Director
Joined: Dec 2005
Posts: 13,515
Likes: 11
From: Fisher, IL
I'll have to look into a temp. gun next time i'm at the auto store.
BUT assuming the engine is hotter than what the gauge says where should I start in hunting down the problem?
BUT assuming the engine is hotter than what the gauge says where should I start in hunting down the problem?
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 330
From: Indy Indiana
there are all sorts of issues calibrating the temp sending unit and the gauge reading.. also you will need to prove that the thermostat is opening when it should and staying open.
i had a 160 theromstat in mine and it would barely move off of cold, I put a 180 in it and the temp gauge shows about 11 oclock now.. am i running to hot? I dunno.. doesn't boil over though..
i had a 160 theromstat in mine and it would barely move off of cold, I put a 180 in it and the temp gauge shows about 11 oclock now.. am i running to hot? I dunno.. doesn't boil over though..
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
If it runs that low on temps and the gauge is 'fairly' accurate, you probably don't have a thermostat in the engine...or the stat is stuck open. It's very little trouble to remove the coolant inlet housing from the intake manifold and see if one is in there, or not. If it is, you can remove it and put it in a pan of water; stick it on the stove and heat it up. If you have a kitchen thermometer, put it in the pan to check the water temp. Note when the stat starts to open and check whether that matches the temp rating stamped in the flange. If it works well [watch its action as it cools, too...to make sure it closes smoothly], just reuse it....but I doubt that will be the case.
If you need to replace it, just stick a 180F stat in there, fire it up, get it warm and see what temp the gauge shows when it stabilizes. If it is within+/- 15 deg. F of what the stat rating was, the stat is working, your cooling system is working and the gauge is working.
If you need to replace it, just stick a 180F stat in there, fire it up, get it warm and see what temp the gauge shows when it stabilizes. If it is within+/- 15 deg. F of what the stat rating was, the stat is working, your cooling system is working and the gauge is working.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
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
Thread Starter
Race Director
Joined: Dec 2005
Posts: 13,515
Likes: 11
From: Fisher, IL
Yeah I think you guys are right.
I need to do some basic maintenance first to see what that actually does.
Was planning on taking the radiator out and having it serviced but didn't know how good a job places around town can actually do with that. Needs the fins straightened, and probably boiled to clean it out?
Not sure if it's worth it or if i should just order a new brass one somewhere.
Then the water pump is rusted over. I either need to take it off and sand blast and paint it or buy a new one.
Then i'll most likely just replace the T-stat....
Then i'll look into the sending unit and gauge after that i guess...
I need to do some basic maintenance first to see what that actually does.
Was planning on taking the radiator out and having it serviced but didn't know how good a job places around town can actually do with that. Needs the fins straightened, and probably boiled to clean it out?
Not sure if it's worth it or if i should just order a new brass one somewhere.
Then the water pump is rusted over. I either need to take it off and sand blast and paint it or buy a new one.
Then i'll most likely just replace the T-stat....
Then i'll look into the sending unit and gauge after that i guess...
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
If you can find a GOOD [general purpose] radiator shop that works on aluminum AND copper rads, just take it to them and ask them to test and make recommendation of whether it can be rebuilt [or not]. If the tanks and fittings are solid, you can have them re-core your radiator with a new like-material core for reasonable money. They will repair/resolder damaged areas and put the same size core in it so that you can just stick it back in the car. No hassle.
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Temp Senders
I have a 73 and have been through several block temp senders and not one is close to the other. The last one I bought from Lectric Unlimited at the Vette fest - guaranteed to be accurate and guess what - it reads about 100 degrees all the time when warm. I think the idea of using an IR gun to determine the actual temp is good. I installed a mechanical temp gauge in the block and get very accurate readings in comparison to the IR gun. Just wish for grins the acutal dash gauge reflected what ws going on.
Pro
Joined: May 2009
Posts: 569
Likes: 2
From: Clio Mi
i just did this experiment today my Factory gauge reads 230 240 omg that's too hot!!!! so i changed the stat to a 160 guess what car ran back up to 230-240 ,, I'm going to burn up my new 496!!, so i got a fancy heat gun. car reads in about 10 locations 160-170 i guess that old gauge sucks! at least now i feel better knowing its not going to overheat!! synopsis the factory gauge and factory sender is about 70 degrees off!!!!!
CF Community Team
Joined: Oct 2004
Posts: 19,357
Likes: 5,242
From: Cape Cod, Mass.
2025 C6 of the Year Finalist - Unmodified
2025 C8 Z06/7/E-Ray of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2021 C8 of the Year Finalist Unmodified
2020 Corvette of the Year Finalist (performance mods)
2019 C1 of Year Winner (performance mods)
2017 Corvette of the Year Finalist
2016 C2 of Year
2015 C3 of Year Finalist
i just did this experiment today my Factory gauge reads 230 240 omg that's too hot!!!! so i changed the stat to a 160 guess what car ran back up to 230-240 ,, I'm going to burn up my new 496!!, so i got a fancy heat gun. car reads in about 10 locations 160-170 i guess that old gauge sucks! at least now i feel better knowing its not going to overheat!! synopsis the factory gauge and factory sender is about 70 degrees off!!!!!
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Perfect reason to install a temporary load to establish whether or not the gauge and wiring are ok.Buy a 2-pack of 70 ohm resistors at Radio Shack.
Install 1 - 70 ohm resistor between green sender wire and block (ground) and the gauge should read very close to 220*
Install 2 - 70 ohm resistors in series for a total of 140 ohms and the gauge should read very close to 160*
Racer
Joined: Jul 2004
Posts: 444
Likes: 0
From: Dallas TX
They'll force a temperature reading on the gauge in the dash. You'll need to disconnect the sending unit, connect the resistor in its place and ground the free end to the block.
Pro
Joined: May 2009
Posts: 569
Likes: 2
From: Clio Mi
Pro
Joined: May 2009
Posts: 569
Likes: 2
From: Clio Mi
My other findings with the infrared gun is if you point it at chrome parts (chrome water neck) it reads very inacurate! about 30 degrees cooler than it really is.. i think it has something to do with the gun trying to send the data back to the gun and the chrome distortes it like a f-117 bomber distortes radar!!
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
I also just bought one of the Lectric Limited sending units and although the gauge reads closer to accurate, it's still way off...
My mechanical gauge reads 175* and the factory gauge is halfway between thw "100" and the first mark(180*?) on the gauge. My original sending unit was a little closer to accurate. On my old motor my mechanical gauge would read 205 and the factory gauge would read 210....in that temp range it was close, but at cooler temp ranges the factory gauge read way too cool.....
Just how they are I guess....I just tuck my mechanical gauge up behind the console under the dash and pull it out to reference from time to time.....sux but...
My mechanical gauge reads 175* and the factory gauge is halfway between thw "100" and the first mark(180*?) on the gauge. My original sending unit was a little closer to accurate. On my old motor my mechanical gauge would read 205 and the factory gauge would read 210....in that temp range it was close, but at cooler temp ranges the factory gauge read way too cool.....
Just how they are I guess....I just tuck my mechanical gauge up behind the console under the dash and pull it out to reference from time to time.....sux but...