I noticed a few days ago that the temperature on my 72 350 was barely getting above 160. I immediately suspected the thermostat. I went ahead and replaced that, only to see the same results. I'm now wondering if the gauge is faulty.

Could I just cut the wire from the sending unit and splice in a new gauge? Or, if the gauge is faulty, is it more than likely the sending unit? Any other ideas?

 

How about using an infrared thermometer to check the temperatures of the thermostat housing and the hoses in and out of the radiator?



- Eric

 

What temp thermostat are you using? What is the temp outside where you are this time of year?

 

I was running a 180 degree tstat. I didn't know what was in there before pulling it. I had decided to go with the factory 195. I live in Buffalo NY so our summer days rarely go above 80 degrees. Of coarse, I only drive the car in the warmer months.

The gauge was working just fine a few days ago, for the two years I've had it in the car. That's why I originally thought a faulty tstat. The infrared thermometer is a good idea. I don't have one though.

 

You can get a cheapie infrared thermometer for a $20-35 at harbor freight. It could be the sending unit, it could be the gauge.

 

... Or Amazon, or WalMart, or eBay, or Home Depot, or Lowes, or...

- Eric

 

Great suggestion on the infrared. Wouldn't have thought of that honestly. Lowes has a solidly rated one for $20 right now. That will give me short term piece of mind if the engine temp is where I think it should be.

 

The engine should be running at least what the thermostat is rated, it should not be less.

 

If I understand how the cooling system works correctly and I am pretty sure I got this correct. The thermostat keeps the coolant in the engine until it reaches the temperature it is designed for. So, a 160 degree thermostat holds the coolant in the engine until it reaches 160 degrees. A 195 degree thermostat holds the coolant in the engine until it reaches 195 degrees. With this in mind that means it keeps the coolant in the radiator also till that temperature is reached in the engine. This would mean a 195 degree thermostat holds the coolant in the radiator longer giving it a better chance to cool than a 160 degree thermostat. This would mean a 195 degree thermostat is better for cooling than a 160 degree thermostat.

I know that they really open and close at a few degrees different than rated. In fact I am sure there is an opening and closing set temp on these. Someone like Joe P. might know that info better. But, for the purpose of this discussion the exact temps it opens and closes it not that critical.

I have been lead to believe that a 195 degree thermostat gives an engine/car a much better chance of cooling than a 160 degrees.

If anyone has better info please help on that.

Larry

 

Basically yes. The thermostat is there to maintain the minimum operating temp of the engine. The radiator and fan (only at idle and very low speed) maintain the maximum temp.

 

Everything you said was good until this.

Coolant moving more slowly through the radiator does not have "more time to cool" than coolant moving faster. Heat transfer rate INCREASES with increasing fluid flowrate, not decreasing. The 190 thermostat holds the coolant in the engine longer (meaning to a higher temperature), not the radiator.

A 195 thermostat is not better for cooling than a 160. They're both the same once they open. The only difference is what temperature they open at. A lower temperature t-stat will keep the engine cooler because it opens at a lower temperature. If there were no thermostat at all in there, the engine would reach operating temperature very slowly if it did at all during the time it was running while you ran to the grocery store or whatever. One common symptom of a failed thermostat that is stuck open is that the heater never provides sufficient heat because the engine never fully warms up. Obviously, one that fails closed will cause overheating.

But running an engine at too cool a temperature can be as harmful to it as running it too hot. The thermostat recommended by the manufacturer is the one that should be used. If the engine overheats or runs too cool with the recommended t-stat, and the engine is otherwise stock, then there is a problem elsewhere in the cooling system or with the engine itself (partial clogs, faulty fan, buildup of deposits, damaged or wrong size radiator, wrong engine timing, etc.).

 

The coolant in the radiator for a longer time cools better is not correct for different reasons. With a 195 degree 'stat the coolant leaves the engine at 195 degrees, yes, but at a very low flow rate. This low flow rate, entering the radiator at 195 deg, is enough to cool the engine.
A thermostat will gradually open, starting about 5-8 degrees above its published temperature (188-193 deg). It is not like switch with a quick on or off.
The thermostat holds the coolant in the engine, and lets a trickle past into the radiator.
A 195 deg 'stat does not automatically increase cooling because of the very low flow.

 

I believe the FLOW rate of one thermostat when open is like that of another. The thermal spring differs to attain the 195 vs 180 or whatnot. The flow at wide open should be the same.

Any "better cooling" from using a 195 vs a 180 would arise from the increased delta T or difference in temp between radiator at 195 where the coolant enters vs ambient air at whatever it is. Coolant at 195 will dump more heat to the air than will coolant at 180, ALL OTHER THINGS UNCHANGED.

Where's the damn Joe P concise nutshell synopsis on this matter?

 

Octania-yes, thermostats of different temp ratings flow about the same. Thermostats of 195 v. 180 degrees cool the engine at different flow rates. If you could control the coolant flow, the coolant temp would decrease as the flow increased. That is another way to say that with a "failed open" 'stat, you cannot get any heat from the heater.