I have seen a bunch of threads on the board about guys thinking their trucks are running hot or too high of an operating temp.

What seems to be a common misconception is the rating of a thermostat. If one is rated at 180 degrees, does this mean the engine cooling water won't go over 180 degrees? No, the rating on the t-stat is the temp at which it opens (Not sure if this the temp it is fully open or not, but believe it is).

Even if you put a 165 degree T-stat in the motor, the motor may still heat the water to above or below 200 degrees. There are a lot of variables in what the operating temp will be. some are definately the condition of the cooling system, the water pump ability to circulate the water, the size of the radiator, pulley size, belt slipage, the flow speed of the water thru the cooling system (specially the speed of the coolant across the cooling area of the radiator.), etc.

Even spark plugs affect the water temp. A colder plug will cause the combustion temps to be lower in the cylinders there by not heating the coolant as much. And the opposite is true of hotter plugs. This happens because the plug dissipates the heat it needs to spark effectively and keep itself from fouling by either rapidly dissipating the heat with a cold plug or not as rapidly with a hotter plug.

Hope some of this helps you understand T-stats and are just my opinions and findings over the years.

 

I disagree on your spark plug theory. The difference between HOT
and COLD spark plugs (heat range) is the temperature that the
center electrode will operate at. The heat range of the spark
plugs should in no way affect the coolant temperature...

 

I'm in agreement with Just Stroken. There are so many variables in maintaining the operating temperature of an engine that to blame the thermostat is an easy out. Thermostats do go bad and are defective from the manufacturer, but going bad they normally stick in the open or closed position and that's easy to determine. I've had several that were off by 5-10 degrees, but feel that's due to incorrect labeling.

If your radiator capacity is adequate, the system sealed, airflow to the radiator adequate, your water pump working correctly, good hoses (spring in the bottom one) the thermostat opening and closing in a proper manner, ignition system correctly timed and with the right plugs, any engine should be able to maintain the thermostat rating at 35mph.

At idle is a different story. Assuming you have no heating problems at 35mph, then it's a problem with drawing enough air over the radiator to disapate the heat from the coolant. That could be fan, fan clutch, shroud, frontal air intake area, engine compartment ability to exit the air flow, collapsed hose or water pump not circulating the coolant fast enough at low rpms.

The most common problem I've seen causing overheating is probably the easiest fix, the radiator cap.

 

Bob,

I agree and disagree with you at the same time.

Yes, I agree with you on the electrode temps in that is what a cold and hot plug is all about and that is what I was trying to get at with my rambling.

But at the same time, if you can't keep the electrode temp at the correct operating temp thereby promoting effective combustion of the fuel and air, then your cylinder temps during combustion will be hot or cold in relationship to the normal cylinder operating temps. Is this not correct? This is very similar in my thinking of a lean air fuel mixture will cause an engine to run hotter than a rich air fuel mixture. The gasoline does have a cooling affect on the cylinder temps.

This will in turn affect the water temps. For is it not the reason we have water circulating in the block and heads for removal of the heat generated by the combustion in each of the cylinders?

Again, these are just my thoughts and understanding on how things work in an internal combustion engine....and I am not an engineer....and I have been known to be wrong in the past and sure I will be wrong again in the future.

George,

I couldn't agree with you more. The radiator cap is probably one of the most over looked items on a car. And even if we look at it, most of us couldn't say if it was good or bad.

 

I've always checked out a "suspect" thermostat that ~looked~ good by putting it in a pan of water on the stove. Take a thermometer and put it in the water and begin heating the water. You should be able to watch the thermostat open at the temperature it's rated at (watch the thermometer)...

As the water cools, you should be able to watch the device close.
Works fine, lasts a long time.

Just a tip from an OLD pro...

 

No, the spark plug heat range DOES NOT determine combustion
temperatures....This is why I said that the spark plug heat range
has not effect on coolant temps...

 

Bob,

I don't know your back ground as you don't know mine, but I would love to hear more indepth as to why you feel the improper heat range of a plug won't affect the combustion chamber temperature or water temperature. Maybe I have missed something during my life time that I need to correct in my ways of thinking.

 

I also will say that plug heat range does by no means affect combustion temperature. Plug heat ranges are simply to prevent pinging/ detonation or on the other hand fouling of the plug. If a plug is too hot, the electrode temperature will actually get to a temperature that will pre- ignite the fuel causing knock, or detonation. On the other hand if a plug is too cold it will not get hot enough to self clean itself and will eventually foul. This is not only me sayin this, it is also automotive text books.

 

I have to go along with Bob and phantom on the plug heat range. I've got a fair amount of experince with superchargers and plug heat range is a big issue for the reasons phantom mentioned in his post. A hotter plug (i.e. shorter electrode) MAY raise combustion temps by 1/2 a degree by having the electrode running at a higher temp, but I doubt it.

Otherwise, I'd say the original post has some good things to consider before panicing because your engine is running 200* with a 180* stat. It's also worth considering that some engines run hot simply by the way they are designed, whether it be on purpose or not (Chubbys thin-walled 305s come to mind).

 

Just Strokin,

The factors that are going to influence combustion temperature
the most will be The amount of air/fuel charge, and the air/fuel
ratio. WOT will cause combustion temps to increase, as well as
a lean mixture......

I hope this helps!!!

 

Well, I am still not totally in agreement with the reasons or whys you are giving that plugs don't affect the coolant temps. After reading the tech info at NGK's website, I still believe the wrong plug slection can adversly affect the coolant temps, maybe not as a directly as I previously mentioned, but definately indirectly as does the coolant/engine temps affect the selection of the spark plug.

http://www.ngksparkplugs.com/techinf...31000&country=

To each their own thinking an opinions and hopefully I haven't ruffled any feathers as I don't feel anyone has ruffled mine with their thoughts or opinions.

 

Just Strokin,

Maybe this will help you:

I think we are in agreement that the plug heat range determines
the operating temperature of the center electrode, correct??

Ok, then think about the volume taken up by the tip of the center
electrode, compared to the rest of the combustion chamber.
Now, which one is going to heat up the other????

 

Bob,

Think of the plug this way, if the heat range selection of the plug can't dissipate the heat for optimal plug operation, then you end up with the tip possibily becoming a glow plug which inturn causes preiginition which leads to additional heat in the chamber which the cooling system has to absorb.

 

Let me ask you this question:

What is making the spark plug tip (electrode) hot???

Isn't it the combustion??????

 

Bob,

As you well know, it could be a number of things, such as lean A-F ratio, wrong heat range plug could cause the tip of the plug to glow. Which goes back to what I first posted about the plug you select for your engine could cause your coolant temps to be high.

Anyway, I have said all I am going to say on this since I still haven't been convienced by you nor the others that spark plug choice won't affect coolant temps in "some cases", whether it elevates the temps or lowers them.

Other Ford-Truck readers and posters, I appoligize to you of this thread got out if hand, but you can use your own wisdom and experience and select any vital info that might be contained in the posts to assist you in dealing with high coolant temperatures.