[Mike68RS]

I though my car was running a little rich (355, 10.3:1, trick flow heads, headers, 750 holley VS,
ect.) so i jetted down to 69's from 70's. I day or so later I noticed my factory temp gauge would quickly peg all the way to hot. I really an not sure I'm "overheating" as there isn't anything coming out of the overflow. I'm running a generic 27x19 aluminum radiator, a summit high flow water pump, factory shroud, 180 degree high flow thermostat with a couple small hole drilled)
I check my gauge with a variable resistor and it seems fine. I also replaced the sending unit with
a "correctly calibrated" united from lectric limited and I still have the same problem. I am running 50/50 with water wetter additive. I guess it could be the stat, but its not even a year old! The upper hose and the drivers side of the radiator is noticibly hotter that the passenger side, if that is any help. I probably am going to try the stat next, but I have that messy job . Any suggestion appreciated. One other question, on the stock temp gauge does anyone know what the temps are at a 1/4, 1/2 3/4 and "H"?

Thanks!
Mike

[JohnZ]

Does your temp gauge peg to full cold when you disconnect the wire at the sending unit and peg to full hot when you ground the sender wire? If it does, the gauge is working. Shoot the upper radiator hose just above the thermostat housing with an I.R. gun and compare that reading with what the gauge shows at the same time so you know what the gauge is really telling you.
[img]graemlins/beers.gif[/img]

[Nantooch]

Maybe your idle was initially just rich but jetting was fine.. Sounds like you went too lean.

[Mike68RS]

My temp gauge does go full cold when disconnected and full hot when shorted, I'm positive it's not the gauge. I might be able to get a hold of the IR gun next week, but I'd rather not wait till then.

I was thinking about the lean condition, but I thought it would only overheat while cruising and not at idle if a too lean condition existed. I don't think 69 jets on my engine is too lean, but I could check the idle mixture adjustment again.

Thanks!
Mike

[Nantooch]

You'd be surprised about the temps. I ran a edelbrock 600 initially and found the engine started to dielse after warm up reguardless of sitting at idle or under revs. When I went to the 750 this stopped and engine temps went back to normal.

[Mike68RS]

Well,
For the heck of it, this morning I changed back to the 70 jets in my Holley 750, took it for a quick spin and the temp gauge is pegged full hot again. When I got back home I opened the hood and this time I was getting some coolant out of the overflow and heard gurgling noises. I guess its likely the most obvious thing in the first place, a bad thermostat. I'll change it tomorrow and let you guys know what happens.

Thanks
Mike

[Mike68RS]

I just got back from changing the thermostat, even though the old one opened o.k. when I tested it in some hot water. Took it out and by the time I got to my friends house (about one mile) who has an infrared gun, the temp needle was pegged full hot again. The gun showed about 174 degrees at the thermostat housing. I let it idle for about 15 minutes and the car did not overheat , but yet the needle remained pegged hot.
I drove it back home turned it off, waited about 15 seconds, restarted the engine and the temp gauge needle read just after the quarter mark. I didn't have time to mess with it anymore tonight, but right now I'm pretty stumped. I'm thinking it is either a wiring or ground problem, but I'm not sure. I'll try to check it out again tomorrow.

Mike

[Nantooch]

May have to trace that wire out then.. Might could be the sending unit is bad.

[Steve W]

Just a note...I tried a "calibrated" lectric limited sending unit on my 66 GTO. It was worthless. I compared the temps with the I.R. gun I got and the readings were better with the Kragen cheapie replacement sending unit.

[Everett#2390]

Sending units are not really calibrated anymore. Hopefully, you have a sender for a gauge and not a switch for a light.

Part number TO-6 comes to mind. I have a 88 Monte Carlo SS. I ordered a s/unit for an 88 SS gauge. Didn't work. Ordered a s/unit for the engine, gauge works fine, first quarter mark is approx 180*F. Middle is approx 210*F.

As JohnZ suggests, use a temp gun to "calibrate" the gauge along with the termostat. Feel the upper hose. When the hose gets hot at t/stat opening, look at the gauge.

[CarlC]

I agree with Everett. The replacement sending units sold by Autometer vary quite a bit. Calibration is required.

[fastercar68]

During my dyno session two weeks ago, they were worried about overheating during the testing. My gauge was pegged at 205*.

When they shot the engine at various points, the highest reading was 195*.

It's an Autometer mechanical temp gauge. I now know to allow 10* before panicing.

[HOTRODSRJ]

Just a few comments from the peanut gallery here.

I would suggest that pegging full hot is a trapped air issue perhaps if you know that the thermostat is opening.

I got bad news for the IR readings! Shooting different metal temps around the engine is not an accurate method of predicting or gauging coolant temps but this could be a GENERAL indicator. You will oft find that the coolant is much hotter. Usually shooting (IR) thermostat housing and adding 5 to 10 degrees is more accurate depending on the design of the housing. The housing just radiates alot of heat off the surfaces making IR readings cold. And you are interested in internal parts moreover which are not on the outside conducting and radiating into free air under the same conditions. They will be hotter, believe me just look at your typical oil temps.

Testing or calibrating gauges outside the car is difficult. Most people drop the sending unit point in a bath of boiling water and go from there. A pan of boiling water can have anything from 170 degree water at the surface to 210 at the bottom. This is not a good method at all and can give you a false security as well as false readings.

Also, even tho I don't think it's at play here, something no one often thinks of is reference voltage. If the reference voltage at the dash is low the readings can be affected as well. Low DC voltage at the dash reference point is common because of the age of the wiring system or the system is not sized properly to handle the current...I see it all the time.

Dieseling when turned off is a carb issue moreover. Usually high idle rpms and overly lean conditions is the cause. Heat just adds to the fray!

[JohnZ]

Originally posted by HOTRODSRJ:
Usually shooting (IR) thermostat housing and adding 5 to 10 degrees is more accurate depending on the design of the housing. The housing just radiates alot of heat off the surfaces making IR readings cold.

That's why I recommend shooting the hose, just above the housing outlet; housings that are painted/polished/glossy really distort the reading, usually 30-40 degrees low.
[img]graemlins/beers.gif[/img]

[Mike68RS]

Just an update to my situation. I removed the temp gauge from the console and wired it directly to the hot, ground and sender terminals and still have the same pegging full problem. I did wire in a thermocouple in the thermostat housing to read the REAL temperature and after a hard drive and long idle, it was reading 187 degrees. So to recap, I have changed the thermostat, tried a different temp sender and checked the wiring by rewiring the gauge directly and bypassing the harness. The only thing left to try is the gauge itself. I do have a temp gauge from 72 Chevelle, I might try it first to see where it reads before buying another Camaro temp gauge.

Still stumped! [img]graemlins/clonk.gif[/img]
Mike