In my 68 SB, I was running hot (~220-230) in 100 degree temps, and discovered a rather large gap (0.75 " at the top, and 2.5" at the bottom) between the fan shroud and the radiator. In the process of closing the gap I gently bumped the shroud on the rad fins and the radiator started leaking. Figuring the radiator was about gone anyway, I bought a new aluminum radiator. I should add that a prev owner replaced the SB Rad with a BB rad and mounts (for better cooling during Texas summers, I presume).

The new rad is also a BB rad so I didn't have to replace the mounts. I've got a new 180* thermostat that tested properly before installation and flushed and replaced the coolant, put in new upper and lower hoses, and fixed the shroud gap.

Now I'm running cool (~120-130) at highway and idle. I have a direct drive 7 blade fan with no clutch. No timing, thermostat, or temp sensor issues that I am aware of unless something failed in the week between the radiator swap.

Questions:

1) any thoughts on whether I should go with and electric or a clutch(preferred) fan,

2) is it possible that the coolant entering the engine is 120-130* and heating to 180* at the thermostat?

Thanks

 

Verify that the guage is correct. If it is, change the thermostat.

 

Shoot the radiator with an infrared gun at the upper radiator hose and one or two points on the radiator to verify that you have a real issue, as the previous owner suggests. Try a local radiator shop for one.

 

The thermostat sets your min. operating temperature.
Your system design/configuration sets your maximum cooling capabilities,
if set up properly it should remain close to the thermostat temp. Rising slightly under heavy demands.
Even with a huge unlimted cooling capabilities you car should be running atleast as hot as your thermostat, unless you don't use one !
If your car is truely running that cool, your thermostat is not closing when it should. 69VETT

 

Appreciate the replies. I've been working on the assumption the the guage and the thermostat are working correctly. They were working one day, then just few days later I changed the radiator and got a better seal between the shroud and the radiator, and now I've gone too cool. It seems too much of a coincidence that the Temp sensor/gauge and/or thermostat go out at exactly the same time as I make all the other cooling system changes.

My though is that the better cooling efficiency of the aluminum radiator and sealing the shroud in connection with a clutchless direct drive fan is giving me too much cooling efficiency. So I was leaning towards a clutch on the fan to get more heat. And while I will probably add a fan clutch, the flaw in my plan is that I haven't addressed why my brand new, freshly tested thermostat isn't doing what it is supposed to. That why I was asking about the water temp increase as it flows through the engine.

Never used a infrared temp meter. Do I need to buy one, or are they commonly rentable?

"If your car is truely running that cool, your thermostat is not closing when it should." 69VETT

You're probably right, I'm just too stubborn to believe it right now.

 

Where are you picking up the temp from? The heads, the intake manifold, or ? As above the thermostat sets the miniumum temp you should see on the gauge.

 

Does your new thermostat have holes drilled in it?

I have a modified stewart thermostat installed with three holes. With the holes you will have coolant flow all the time, even if your thermostat is closed.

My temperature is always below the thermostat setting when I'm cruising below 40 mph.

 

You may have a lot of trapped air in the engine so that the water level is below the temp sensor and not really reading it at all. Remove your radiator cap and start the car. If the rad fluid level gets lower, fill it up [not overfilled, if you don't have an overflow bottle]. Let the car get to operating temp and the stat should open up so that you see coolant flowing in the fill hole. If the coolant drops more, you had air trapped in the system...add more to where you want the coolant when HOT. Put the rad cap on and see how it drives and what temp it runs. Good luck.

 

Temp sensor is on the right side head near #2 cylinder.

No holes in the thermostat.

Given the location of the sensor, I doubt it has trapped air that low. The coolant level in the radiator is higher than the level of the sensor and is currently full. I did all the proper procedures to get the air out when I filled, and the system took the same amount as came out (although the radiator capacities might be a little different). On the first cool down cycle, I only lost about a pint out of the overflow reservoir and there is still some in it. I haven't run it since.