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Running to cool. What can happen?

afd516

NAXJA Forum User
Location
Fort Worth, Tx
I have read plenty of threads about vehicles running to cool and what to do to try to fix them.In none of the threads is the mention of why you don't want your vehicle to run at, let's say, 140-150 degrees.

I do not have this problem right now but, have before. I did't try to fix it. Instead, I got rid of the car. I never saw any issues with it or nor have I heard of any issues with "underheating".

Just trying to learn. Thanks
 
The ECU is not controlling the engine, Your gas mileage will be poor, no heat, poor performance, clearances in the engine will not be correct causing wear, will not pass emission test.
 
If you run too cool in a car with electronic engine management, there's a good chance that the computer will never enter into its normal running mode, and fuel economy and emissions will suffer. In general, an engine works more efficiently hot, and the trick is to get it good and hot without melting it. This is one reason we now have cars with pressurized cooling systems that allow the coolant to heat up beyond 212º without boiling.

I seem to recall that some years ago one of the noted racers at Lime Rock, perhaps Sam Posey, was doing research on very high temp gas engines, using exotic materials, but I can't find any references to that on the web. As I recall, their showpiece was a Honda engine with ceramic innards that ran with no coolant at all.
 
There is another reason you don't want to run too cool. The oil needs to get hot enought to boil off any moisture in the system. Water + Oil = H2SO4 (sulphuric acid) and you end up with tons of sludge. That is why short trips to the store and no highway miles is hard on the engine.
 
That is some good info. So, what would be optimal for the 4.0L. 180 degrees or 210 degrees. Does it mater as long as it is in between those temps? Mine runs between 165 and 190 is this ok?
 
The standard thermostat should be 195. Operating temps should be at least 195
 
Also both or you, the dash temperature gauge is often not accurate, the older it gets the worst it gets.
So before you start fixing things make sure what the temperature really is.
 
Whats the best way to go about getting the actual temperature, just about everything in my cooling system has been replaced (more preventative then anything else, it sat for a long time) but the temperature gauge still reads rather high all of the time. Before i go replacing the radiator (not that its a huge expense, or alot of work) id like to know what its actually running at.
 
JoeShmo said:
Whats the best way to go about getting the actual temperature, just about everything in my cooling system has been replaced (more preventative then anything else, it sat for a long time) but the temperature gauge still reads rather high all of the time. Before i go replacing the radiator (not that its a huge expense, or alot of work) id like to know what its actually running at.
Replace BOTH temp sensors, there one for the ECU and one for the gauge. To read the temperture you need a lazer gun.
 
Fast response. Do you happen to know at around what temperature the electric fan is supposed to kick on, because the only time ive heard it spool up was when i had it idling in my driveway for ages, and the gauge was at the last line before the red (dont let it get this high ever, other than trying to see if the fan would kick on). If it actually kicks in around 210, it would be a dead giveaway that the gauge is off (and the rad. temp sensor for the fan has already been replaced)
 
JoeShmo said:
Fast response. Do you happen to know at around what temperature the electric fan is supposed to kick on, because the only time ive heard it spool up was when i had it idling in my driveway for ages, and the gauge was at the last line before the red (dont let it get this high ever, other than trying to see if the fan would kick on). If it actually kicks in around 210, it would be a dead giveaway that the gauge is off (and the rad. temp sensor for the fan has already been replaced)
218 degrees
 
So the fact that it doesnt come on (with a new sensor) until my gauge reads way above that would definately make the gauge being off a possibilty? If so, time to go and grab another overpriced sensor (or 2)
 
If I were to replace the gauge, what should I go with? Oem, Autometer,VDO, etc. Does it matter as long as it is new? I have seen the style with the copper line that travels from the engine to the gauge. Is this a good type to go with or is there anothor style that I should look for?
 
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