Just completed a body-off on a 67 L-79 Coupe. Block came out 0.20 over, new Dewitts radiator. Rebuilt water pump. Thermostat 180 w-1/8" hole. New radiator cap(repo R-26). Timing 10 deg and vac working ( manifold source), 5 blade and stops turning with engine when shut off.
Here is the issue. Idling for long periods cause the temp gauge to move up slow. I will let her idle and after a while she is moving up past 210. IR gun at sender shows the same reading. If I take her out for a ride 35MPH she cools down to about 11 o'clock and stays there till you stop at long lights.
A friend showed me the owners manual that says 210 is normal and will go higher in stop and go and extended idle? Just does not seem right. I would think the system had been engineered to idle all day and stay cool. I have never let her go to see that happens and she has not boiled over. I shut it off when the IR gun is showing about 215 or so..
It also seems like the temp drop from radiator inlet and outlet is not too great 20-30 deg?? Im thinking there is an issue with air movement at idle.
Does this seem normal to you guys? Maybe I am expecting to much..
Thanks, Kurt

 

Assuming you have the correct shroud and fan in place, those are symptoms of inadequate idle airflow - usually it's the fan clutch. Temp check to verify gauge reading with the I.R. gun should be done on the upper radiator hose, just above the thermostat housing, not on the sending unit. Do that check again to see what the gauge is really telling you.

 

Correct fan and shroud. Why check the hose with the IR gun?? Would the rubber give incorrect readings? I shut off the motor and the fan stops with the engine. I am going to try a clutch anyway. I have a small shop fan I am going to direct into the radiator to see if this added air will stabilize the temps at idle. Thanks for the feedback.. Kurt

 

Kurt,

The rubber gives you an accurate reading because it does not reflect at all. The metal is reflective and gives you a higher reading with an IR gun. Dave

 

If you open the hood and leave it idle, will it cool to normal 170-180F?

 

There are times when temperature and humidity can affect your cooling.

 

Hood open or closed it starts to very slowly get hotter. I have not just let her go to see if it ever levels off. I will shut her off at about 215-220. I hate to hurt a fresh motor. 80 deg day and she still heats up...

 

Look in the rad at the water flow at idle. Blip the throttle up a little. It seems that at a low idle some pumps provide almost no flow. If that's the case bump up the idle a little.....found that out on my car!

 

I would question the idea of using the IR gun to measure the hose instead of the water neck. There is no laser or reflectivity issue involved with these devices (some do use a visible laser but that is just so you the user can see where you are shooting it is not part of the temp measuring system) Measuring the hose will most likely result in a lower temp reading but that is because the hose is a much better insulator than the metal neck. And you want the temp of the water which will be passed through the metal much faster than through the hose, hence the neck surface will be closer to the water temp faster than the hose. On top of which at slow speeds the hose might not even be full allowing the top of the hose to be cooler than the bottom that actually contacts the water. In theory all the temps would eventually even out in time but it might take longer than you want to let things go.

I concur this sounds like an air flow or water flow problem. Using the fan to blow through sounds like a good possible test, also maybe plugging the big bypass line on the intake so water is forced through the radiator (assuming the thermostat opens)...at idle you may not have enough water flow especially if you have non standard pulleys or a 'weak pump'

Darren